| 1. |
- Locke, Adam E, et al.
(författare)
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Genetic studies of body mass index yield new insights for obesity biology.
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 518:7538, s. 197-401
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Tidskriftsartikel (refereegranskat)abstract
- Obesity is heritable and predisposes to many diseases. To understand the genetic basis of obesity better, here we conduct a genome-wide association study and Metabochip meta-analysis of body mass index (BMI), a measure commonly used to define obesity and assess adiposity, in up to 339,224 individuals. This analysis identifies 97 BMI-associated loci (P < 5 × 10(-8)), 56 of which are novel. Five loci demonstrate clear evidence of several independent association signals, and many loci have significant effects on other metabolic phenotypes. The 97 loci account for ∼2.7% of BMI variation, and genome-wide estimates suggest that common variation accounts for >20% of BMI variation. Pathway analyses provide strong support for a role of the central nervous system in obesity susceptibility and implicate new genes and pathways, including those related to synaptic function, glutamate signalling, insulin secretion/action, energy metabolism, lipid biology and adipogenesis.
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| 2. |
- Shungin, Dmitry, et al.
(författare)
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New genetic loci link adipose and insulin biology to body fat distribution.
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 518:7538, s. 187-378
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Tidskriftsartikel (refereegranskat)abstract
- Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms.
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| 3. |
- Alberto, H. V., et al.
(författare)
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Slow-muon study of quaternary solar-cell materials : Single layers and p-n junctions
- 2018
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Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 2:2
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Tidskriftsartikel (refereegranskat)abstract
- Thin films and p-n junctions for solar cells based on the absorber materials Cu(In, Ga) Se-2 and Cu2ZnSnS4 were investigated as a function of depth using implanted low energy muons. The most significant result is a clear decrease of the formation probability of the Mu(+) state at the heterojunction interface as well as at the surface of the Cu(In, Ga)Se-2 film. This reduction is attributed to a reduced bonding reaction of the muon in the absorber defect layer at its surface. In addition, the activation energies for the conversion from a muon in an atomiclike configuration to a anion-bound position are determined from temperature-dependence measurements. It is concluded that the muon probe provides a measurement of the effective surface defect layer width, both at the heterojunctions and at the films. The CIGS surface defect layer is crucial for solar-cell electrical performance and additional information can be used for further optimizations of the surface.
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| 4. |
- Bose, Sourav, et al.
(författare)
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A morphological and electronic study of ultrathin rear passivated Cu(In,Ga)Se2 solar cells
- 2019
-
Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 671, s. 77-84
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Tidskriftsartikel (refereegranskat)abstract
- The effects of introducing a passivation layer at the rear of ultrathin Copper Indium Gallium di-Selenide Cu(In,Ga)Se2 (CIGS) solar cells is studied. Point contact structures have been created on 25 nm Al2O3 layer using e-beam lithography. Reference solar cells with ultrathin CIGS layers provide devices with average values of light to power conversion efficiency of 8.1% while for passivated cells values reached 9.5%. Electronic properties of passivated cells have been studied before, but the influence of growing the CIGS on Al2O3 with point contacts was still unknown from a structural and morphological point of view. Scanning Electron Microscopy, X-ray Diffraction and Raman spectroscopy measurements were performed. These measurements revealed no significant morphological or structural differences in the CIGS layer for the passivated samples compared with reference samples. These results are in agreement with the similar values of carrier density (~8 x 1016 cm-3) and depletion region (~160 nm) extracted using electrical measurements. A detailed comparison between both sample types in terms of current-voltage, external quantum efficiency and photoluminescence measurements show very different optoelectronic behaviour which is indicative of a successful passivation. SCAPS simulations are done to explain the observed results in view of passivation of the rear interface.
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| 5. |
- Cunha, J. M. V., et al.
(författare)
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Insulator Materials for Interface Passivation of Cu(In,Ga)Se-2 Thin Films
- 2018
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Ingår i: IEEE Journal of Photovoltaics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2156-3381 .- 2156-3403. ; 8:5, s. 1313-1319
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Tidskriftsartikel (refereegranskat)abstract
- In this work, metal-insulator-semiconductor structures were fabricated in order to study different types of insulators, namely, aluminum oxide (Al2O3), silicon nitride, and silicon oxide (SiOx) to be used as passivation layers in Cu(In,Ga)Se-2 (CIGS) thin-film solar cells. The investigated stacks consisted of SLG/Mo/CIGS/insulator/Al. Raman scattering and photoluminescence measurements were done to verify the insulator deposition influence on the CIGS surface. In order to study the electrical properties of the CIGS-insulator interface, capacitance versus conductance and voltage (C-G-V) measurements were done to estimate the number and polarity of fixed insulator charges (Q(f)). The density of interface defects (D-it) was estimated from capacitance versus conductance and frequency (C-G-f) measurements. This study evidences that the deposition of the insulators at high temperatures (300 degrees C) and the use of a sputtering technique cause surface modification on the CIGS surface. We found that, by varying the SiOx deposition parameters, it is possible to have opposite charges inside the insulator, which would allow its use in different device architectures. The material with lower Dit values was Al2O3 when deposited by sputtering.
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| 6. |
- Curado, M. A., et al.
(författare)
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Front passivation of Cu(In,Ga)Se-2 solar cells using Al2O3 : Culprits and benefits
- 2020
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Ingår i: APPLIED MATERIALS TODAY. - : ELSEVIER. - 2352-9407. ; 21
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Tidskriftsartikel (refereegranskat)abstract
- In the past years, the strategies used to break the Cu(In,Ga)Se-2 (CIGS) light to power conversion efficiency world record value were based on improvements of the absorber optoelectronic and crystalline properties, mainly using complex post-deposition treatments. To reach even higher efficiency values, further advances in the solar cell architecture are needed, in particular, with respect to the CIGS interfaces. In this study, we evaluate the structural, morphological and optoelectronic impact of an Al2O3 layer as a potential front passivation layer on the CIGS properties, as well as an Al2O3 tunneling layer between CIGS and CdS. Morphological and structural analyses reveal that the use of Al2O3 alone is not detrimental to CIGS, although it does not resist to the CdS chemical bath deposition. The CIGS optoelectronic properties degrade when the CdS is deposited on top of Al2O3. Nonetheless, when Al2O3 is used alone, the optoelectronic measurements reveal a positive impact of this inclusion such as a very low concentration of interface defects while keeping the same CIGS recombination channels. Thus, we suggest that an Al2O3 front passivation layer can be successfully used with alternative buffer layers. Depth-resolved microscopic analysis of the CIGS interface with slow-muons strongly suggests for the first time that low-energy muon spin spectroscopy (LE-mu SR) is sensitive to both charge carrier separation and bulk recombination in complex semiconductors. The demonstration that Al2O3 has the potential to be used as a front passivation layer is of significant importance, considering that Al2O3 has been widely studied as rear interface passivation material. (C) 2020 Published by Elsevier Ltd.
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| 7. |
- Fernandes, P. A., et al.
(författare)
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Phase selective growth of Cu12Sb4S13 and Cu3SbS4 thin films by chalcogenization of simultaneous sputtered metal precursors
- 2019
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 797, s. 1359-1366
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present a procedure to grow Cu12Sb4S13 and Cu3SbS4 thin films consisting of the deposition of simultaneously sputtered metal precursors followed by a annealing treatment in a sulphur atmosphere. The selection of the ternary phase is performed by adjusting the sulphur evaporation temperature in the chalcogenization process. It is shown that for a sulphur evaporation temperature of 140 °C the predominant phase is Cu12Sb4S13 while for 180 °C the predominant phase is Cu3SbS4. In order to ensure precursor composition homogeneity, the Cu-Sb metallic precursors are deposited simultaneously by RF magnetron sputtering using adjustable segmented targets. The morphological characterization of the films was made by scanning electron microscopy and the composition was analysed by energy dispersive spectroscopy. The structural analysis and phase identification were performed by X-ray diffraction and Raman scattering. The optical properties were studied on films deposited directly on bare glass and the optical bandgap energies of 1.47 eV and 0.89 eV for Cu12Sb4S13 and Cu3SbS4, respectively, were determined.
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| 8. |
- Lopes, T. S., et al.
(författare)
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Cu(In,Ga)Se2 based ultrathin solar cells the pathway from lab rigid to large scale flexible technology
- 2023
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Ingår i: npj Flexible Electronics. - : Springer Nature. - 2397-4621. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- The incorporation of interface passivation structures in ultrathin Cu(In,Ga)Se2 based solar cells is shown. The fabrication used an industry scalable lithography technique—nanoimprint lithography (NIL)—for a 15 × 15 cm2 dielectric layer patterning. Devices with a NIL nanopatterned dielectric layer are benchmarked against electron-beam lithography (EBL) patterning, using rigid substrates. The NIL patterned device shows similar performance to the EBL patterned device.The impact of the lithographic processes in the rigid solar cells’ performance were evaluated via X-ray Photoelectron Spectroscopy and through a Solar Cell Capacitance Simulator. The device on stainless-steel showed a slightly lower performance than the rigid approach, due to additional challenges of processing steel substrates, even though scanning transmission electron microscopy did not show clear evidence of impurity diffusion. Notwithstanding, time-resolved photoluminescence results strongly suggested elemental diffusion from the flexible substrate. Nevertheless, bending tests on the stainless-steel device demonstrated the mechanical stability of the CIGS-based device.
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| 9. |
- Alberto, H. V., et al.
(författare)
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Low energy muon study of the p-n interface in chalcopyrite solar cells
- 2023
-
Ingår i: Journal of Physics, Conference Series. - : Institute of Physics Publishing (IOPP). - 1742-6588 .- 1742-6596. ; 2462
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Tidskriftsartikel (refereegranskat)abstract
- The slow muon technique was used to study the p-n junction of chalcopyrite solar cells. A defect layer near the interface was identified and the passivation of the defects by buffer layers was studied. Several cover layers on top of the chalcopyrite Cu(In,Ga)Se2 (CIGS) semiconductor absorber were investigated in this work, namely CdS, ZnSnO, Al2O3 and SiO2. Quantitative results were obtained: The defect layer extends about 50 nm into the CIGS absorber, the relevant disturbance is strain in the lattice, and CdS provides the best passivation, oxides have a minor effect. In the present contribution, specific aspects of the low-energy muon technique in connection with this research are discussed.
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| 10. |
- Ben Sedrine, N., et al.
(författare)
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Fluctuating potentials in GaAs : Si nanowires: Critical reduction of the influence of polytypism on the electronic structure
- 2018
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 10:8, s. 3697-3708
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the effects of Si doping in GaAs nanowires (NWs) grown on GaAs (111)B by molecular beam epitaxy with different Si doping levels (nominal free carrier concentrations of 1 × 1016, 8 × 1016, 1 × 1018 and 5 × 1018 cm-3) are deeply investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), grazing incidence X-ray diffraction (GID), photoluminescence (PL) and cathadoluminescence (CL). TEM results reveal a mixture of wurtzite (WZ) and zinc-blende (ZB) segments along the NW axis independently of the Si doping levels. GID measurements suggest a slight increase of the ZB fraction with the Si doping. Low temperature PL and CL spectra exhibit sharp lines in the energy range 1.41-1.48 eV, for the samples with lower Si doping levels. However, the emission intensity increases and is accompanied by a clear broadening of the observed lines for the samples with higher Si doping levels. The staggered type-II band alignment only determines the optical properties of the lower doping levels in GaAs:Si NWs. For the higher Si doping levels, the electronic energy level structure of the NWs is determined by electrostatic fluctuating potentials intimately related to the amphoteric behavior of the Si dopant in GaAs. For the heavily doped NWs, the estimated depth of the potential wells is ∼96-117 meV. Our results reveal that the occurrence of the fluctuating potentials is not dependent on the crystalline phase and shows that the limitation imposed by the polytypism can be overcome.
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| 11. |
- Hartley, Philippa, et al.
(författare)
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SKA Science Data Challenge 2: analysis and results
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 523:2, s. 1967-1993
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Tidskriftsartikel (refereegranskat)abstract
- The Square Kilometre Array Observatory (SKAO) will explore the radio sky to new depths in order to conduct transformational science. SKAO data products made available to astronomers will be correspondingly large and complex, requiring the application of advanced analysis techniques to extract key science findings. To this end, SKAO is conducting a series of Science Data Challenges, each designed to familiarize the scientific community with SKAO data and to drive the development of new analysis techniques. We present the results from Science Data Challenge 2 (SDC2), which invited participants to find and characterize 233 245 neutral hydrogen (H i) sources in a simulated data product representing a 2000 h SKA-Mid spectral line observation from redshifts 0.25-0.5. Through the generous support of eight international supercomputing facilities, participants were able to undertake the Challenge using dedicated computational resources. Alongside the main challenge, 'reproducibility awards' were made in recognition of those pipelines which demonstrated Open Science best practice. The Challenge saw over 100 participants develop a range of new and existing techniques, with results that highlight the strengths of multidisciplinary and collaborative effort. The winning strategy - which combined predictions from two independent machine learning techniques to yield a 20 per cent improvement in overall performance - underscores one of the main Challenge outcomes: that of method complementarity. It is likely that the combination of methods in a so-called ensemble approach will be key to exploiting very large astronomical data sets.
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| 12. |
- Leitao, J. P., et al.
(författare)
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Influence of CdS and ZnxSn1-xOy Buffer Layers on the Photoluminescence of Cu(In,Ga)Se2 Thin Films
- 2016
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Ingår i: 2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC). - New York : IEEE. - 9781509027248 ; , s. 3068-3071
-
Konferensbidrag (refereegranskat)abstract
- In this work, an optical study by photoluminescence on the influence of different buffer layers on a Cu(In, Ga)Se2 (CIGS) thin film is presented. Chemical bath deposited CdS was compared with atomic layer deposited ZnxSn1xOy (ZnSnO). The CIGS bulk and CIGS/buffer interface in both samples are strongly influenced by fluctuating potentials, being less pronounced for the sample with the ZnSnO buffer layer. This study emphasizes the potential application of the ZnSnO semiconductor in CIGS based solar cells.
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| 13. |
- Ried, Janina S., et al.
(författare)
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A principal component meta-analysis on multiple anthropometric traits identifies novel loci for body shape
- 2016
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Large consortia have revealed hundreds of genetic loci associated with anthropometric traits, one trait at a time. We examined whether genetic variants affect body shape as a composite phenotype that is represented by a combination of anthropometric traits. We developed an approach that calculates averaged PCs (AvPCs) representing body shape derived from six anthropometric traits (body mass index, height, weight, waist and hip circumference, waist-to-hip ratio). The first four AvPCs explain >99% of the variability, are heritable, and associate with cardiometabolic outcomes. We performed genome-wide association analyses for each body shape composite phenotype across 65 studies and meta-analysed summary statistics. We identify six novel loci: LEMD2 and CD47 for AvPC1, RPS6KA5/C14orf159 and GANAB for AvPC3, and ARL15 and ANP32 for AvPC4. Our findings highlight the value of using multiple traits to define complex phenotypes for discovery, which are not captured by single-trait analyses, and may shed light onto new pathways.
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| 14. |
- Salome, Pedro M. P., et al.
(författare)
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A comparison between thin film solar cells made from co-evaporated CuIn1-xGaxSe2 using a one-stage process versus a three-stage process
- 2015
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Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 23:4, s. 470-478
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Tidskriftsartikel (refereegranskat)abstract
- Until this day, the most efficient Cu(In,Ga)Se-2 thin film solar cells have been prepared using a rather complex growth process often referred to as three-stage or multistage. This family of processes is mainly characterized by a first step deposited with only In, Ga and Se flux to form a first layer. Cu is added in a second step until the film becomes slightly Cu-rich, where-after the film is converted to its final Cu-poor composition by a third stage, again with no or very little addition of Cu. In this paper, a comparison between solar cells prepared with the three-stage process and a one-stage/in-line process with the same composition, thickness, and solar cell stack is made. The one-stage process is easier to be used in an industrial scale and do not have Cu-rich transitions. The samples were analyzed using glow discharge optical emission spectroscopy, scanning electron microscopy, X-ray diffraction, current-voltage-temperature, capacitance-voltage, external quantum efficiency, transmission/reflection, and photoluminescence. It was concluded that in spite of differences in the texturing, morphology and Ga gradient, the electrical performance of the two types of samples is quite similar as demonstrated by the similar J-V behavior, quantum spectral response, and the estimated recombination losses.
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| 15. |
- Salome, P. M. P., et al.
(författare)
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CdS and Zn1-xSnxOy buffer layers for CIGS solar cells
- 2017
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 159, s. 272-281
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Tidskriftsartikel (refereegranskat)abstract
- Thin film solar cells based on Cu(In,Ga)Se-2 (CIGS), where just the buffer layer is changed, were fabricated and studied. The effects of two different buffer layers, CdS and Zn1-xSnxOy (ZnSnO), are compared using several characterization techniques. We compared both devices and observe that the ZnSnO-based solar cells have similar values of power conversion efficiency as compared to the cells with CdS buffer layers. The ZnSnO-based devices have higher values in the short-circuit current (6) that compensate for lower values in fill factor (FF) and open circuit voltage (V-oc) than CdS based devices. Kelvin probe force microscopy (KPFM) results indicate that CdS provides junctions with slightly higher surface photovoltage (SPV) than ZnSnO, thus explaining the lower Voc potential for the ZnSnO sample. The TEM analysis shows a poly-crystalline ZnSnO layer and we have not detected any strong evidence of diffusion of Zn or Sn into the CIGS. From the photoluminescence measurements, we concluded that both samples are being affected by fluctuating potentials, although this effect is higher for the CdS sample.
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| 16. |
- Sousa, M. G., et al.
(författare)
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Cu2ZnSnS4 absorber layers obtained through sulphurization of metallic precursors : Graphite box versus sulphur flux
- 2013
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 535, s. 27-30
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Tidskriftsartikel (refereegranskat)abstract
- In this work we employed a hybrid method, combining RF-magnetron sputtering with evaporation, for the deposition of tailor made metallic precursors, with varying number of Zn/Sn/Cu (ZTC) periods and compared two approaches to sulphurization. Two series of samples with 1x, 2x and 4x ZTC periods have been prepared. One series of precursors was sulphurized in a tubular furnace directly exposed to a sulphur vapour and N-2 + 5% H-2 flux at a pressure of 5.0 x 10(+4) Pa. A second series of identical precursors was sulphurized in the same furnace but inside a graphite box where sulphur pellets have been evaporated again in the presence of N-2 + 5% H-2 and at the same pressure as for the sulphur flux experiments. The morphological and chemical analyses revealed a small grain structure but good average composition for all three films sulphurized in the graphite box. As for the three films sulphurized in sulphur flux grain growth was seen with the increase of the number of ZTC periods whilst, in terms of composition, they were slightly Zn poor. The films' crystal structure showed that Cu2ZnSnS4 is the dominant phase. However, in the case of the sulphur flux films SnS2 was also detected. Photoluminescence spectroscopy studies showed an asymmetric broad band emission which occurs in the range of 1-1.5 eV. Clearly the radiative recombination efficiency is higher in the series of samples sulphurized in sulphur flux. We have found that sulphurization in sulphur flux leads to better film morphology than when the process is carried out in a graphite box in similar thermodynamic conditions. Solar cells have been prepared and characterized showing a correlation between improved film morphology and cell performance. The best cells achieved an efficiency of 2.4%.
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| 17. |
- Teixeira, J. P., et al.
(författare)
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Evidence of Limiting Effects of Fluctuating Potentials on V-OC of Cu(In, Ga)Se-2 Thin-Film Solar Cells
- 2019
-
Ingår i: Physical Review Applied. - 2331-7019. ; 11:5
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a consistent theoretical approach and an extensive experimental study of Cu(In, Ga)Se-2- (CIGS-)based solar cells to investigate the influence of fluctuating potentials on the limitations of solar-cell performance. The absorptance is calculated for extensions to the Shockley-Queisser model involving the description of tail states under the Urbach-rule, optimal-fluctuation-theory, and bandgap-fluctuation models, as well as the expected values for the saturation current density, short-circuit current density, and open-circuit voltage (V-OC). Three CIGS-based solar cells with [Cu]/([Ga]+[In]) ratios of 0.53, 0.71, and 0.84 are grown to intentionally have sufficiently different amplitudes of fluctuating potentials. We show both theoretically and experimentally the role played by fluctuating potentials, in particular in the V-OC losses. We provide evidence for a higher degree of correlation of electrostatic fluctuating potentials with V-OC losses in comparison with band-gap fluctuations. Additionally, our results show the influence of fluctuating potentials not just at low temperature but also at room temperature.
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| 18. |
- Teixeira, Jennifer P., et al.
(författare)
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Recombination Channels in Cu(In,Ga)Se2 Thin Films : Impact of the Ga-Profile
- 2020
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:23, s. 12295-12304
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Tidskriftsartikel (refereegranskat)abstract
- Depth bandgap profiles via a [Ga]/([Ga]+[In]) variation in the Cu(In,Ga)Se-2 (CIGS) absorber layer have been implemented as a strategy to enhance the performance of CIGS solar cells. Since the [Ga]/([Ga]+[In]) determines to a large extent the position of the conduction band minimum, different Ga-profiles lead to different electronic energy levels structures throughout the CIGS layer. In this paper, from the investigation of the dependence of the photoluminescence (PL) on excitation power and temperature, we critically analyze the impact of a notch or a linear Ga-profile on the CIGS electronic energy levels structure and subsequent dominant recombination channels. Notwithstanding, two radiative transitions involving fluctuating potentials were observed for each sample, and significant differences in the luminescence resulting from the two Ga-profiles were identified. For the CIGS absorber with a notch Ga-profile, two tail-impurity radiative transitions involving equivalent donor clusters and the same deep acceptor level were ascribed to the CIGS/CdS interface region and to the notch region. The probability of radiative recombination in these two regions is discussed. For the CIGS absorber with a linear Ga-profile, two band-impurity radiative transitions involving an acceptor, with an ionization energy compatible with the V-Cu defect were ascribed to the CIGS/CdS interface region. Our results show that the dominant acceptor defects are dependent on the Ga-profile, and they also highlight the complexity of the radiative and nonradiative recombination channels revealed by the tight control of the parameters in the experiment.
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| 19. |
- Brawand, David, et al.
(författare)
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The genomic substrate for adaptive radiation in African cichlid fish
- 2014
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 513:7518, s. 375-381
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Tidskriftsartikel (refereegranskat)abstract
- Cichlid fishes are famous for large, diverse and replicated adaptive radiations in the Great Lakes of East Africa. To understand themolecular mechanisms underlying cichlid phenotypic diversity, we sequenced the genomes and transcriptomes of five lineages of African cichlids: the Nile tilapia (Oreochromis niloticus), an ancestral lineage with low diversity; and four members of the East African lineage: Neolamprologus brichardi/pulcher (older radiation, Lake Tanganyika), Metriaclima zebra (recent radiation, Lake Malawi), Pundamilia nyererei (very recent radiation, Lake Victoria), and Astatotilapia burtoni (riverine species around Lake Tanganyika). We found an excess of gene duplications in the East African lineage compared to tilapia and other teleosts, an abundance of non-coding element divergence, accelerated coding sequence evolution, expression divergence associated with transposable element insertions, and regulation by novel microRNAs. In addition, we analysed sequence data from sixty individuals representing six closely related species from Lake Victoria, and show genome-wide diversifying selection on coding and regulatory variants, some of which were recruited from ancient polymorphisms. We conclude that a number of molecular mechanisms shaped East African cichlid genomes, and that amassing of standing variation during periods of relaxed purifying selection may have been important in facilitating subsequent evolutionary diversification.
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| 20. |
- Fernandes, P. A., et al.
(författare)
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Thermodynamic pathway for the formation of SnSe and SnSe2 polycrystalline thin films by selenization of metal precursors
- 2013
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Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 15:47, s. 10278-10286
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Tidskriftsartikel (refereegranskat)abstract
- In this work, tin selenide thin films (SnSex) were grown on soda lime glass substrates by selenization of dc magnetron sputtered Sn metallic precursors. Selenization was performed at maximum temperatures in the range 300 degrees C to 570 degrees C. The thickness and the composition of the films were analysed using step profilometry and energy dispersive spectroscopy, respectively. The films were structurally and optically investigated by X-ray diffraction, Raman spectroscopy and optical transmittance and reflectance measurements. X-Ray diffraction patterns suggest that for temperatures between 300 degrees C and 470 degrees C, the films are composed of the hexagonal-SnSe2 phase. By increasing the temperature, the films selenized at maximum temperatures of 530 degrees C and 570 degrees C show orthorhombic-SnSe as the dominant phase with a preferential crystal orientation along the (400) crystallographic plane. Raman scattering analysis allowed the assignment of peaks at 119 cm(-1) and 185 cm(-1) to the hexagonal-SnSe2 phase and those at 108 cm(-1), 130 cm(-1) and 150 cm(-1) to the orthorhombic-SnSe phase. All samples presented traces of condensed amorphous Se with a characteristic Raman peak located at 255 cm(-1). From optical measurements, the estimated band gap energies for hexagonal-SnSe2 were close to 0.9 eV and 1.7 eV for indirect forbidden and direct transitions, respectively. The samples with the dominant orthorhombic-SnSe phase presented estimated band gap energies of 0.95 eV and 1.15 eV for indirect allowed and direct allowed transitions, respectively.
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| 21. |
- Salome, Pedro M. P., et al.
(författare)
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Influence of CdS and ZnSnO Buffer Layers on the Photoluminescence of Cu(In,Ga)Se-2 Thin Films
- 2017
-
Ingår i: IEEE Journal of Photovoltaics. - : Institute of Electrical and Electronics Engineers (IEEE). - 2156-3381 .- 2156-3403. ; 7:2, s. 670-675
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Tidskriftsartikel (refereegranskat)abstract
- The search for alternatives to the CdS buffer layer in Cu(In,Ga)Se-2 (CIGS) solar cells has turned out to be quite promising in terms of power conversion efficiency. In this paper, the typically used chemical-bath-deposited CdS layer is compared with an atomic-layer-deposited Zn1-xSnxOy (ZnSnO). An optical study by external quantum efficiency and photoluminescence on the influence of different buffer layers on the defect properties of CIGS is presented. For both buffer layers, the CIGS bulk and CIGS/buffer interface are strongly influenced by electrostatic fluctuating potentials, which are less pronounced for the sample with the ZnSnO buffer layer. This is associated with a lower concentration of donor defects at the CIGS near-interface layer. A change in the bandgap of the CIGS as a consequence of the buffer layer deposition is observed. This study expands the knowledge of defects in the complex quaternary semiconductor CIGS, which, as discussed, can be affected even by the choice of buffer layer and its deposition process.
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| 22. |
- Salome, Pedro M. P., et al.
(författare)
-
Passivation of Interfaces in Thin Film Solar Cells : Understanding the Effects of a Nanostructured Rear Point Contact Layer
- 2018
-
Ingår i: Advanced Materials Interfaces. - : Wiley. - 2196-7350. ; 5:2
-
Tidskriftsartikel (refereegranskat)abstract
- Thin film solar cells based in Cu(In,Ga)Se-2 (CIGS) are among the most efficient polycrystalline solar cells, surpassing CdTe and even polycrystalline silicon solar cells. For further developments, the CIGS technology has to start incorporating different solar cell architectures and strategies that allow for very low interface recombination. In this work, ultrathin 350 nm CIGS solar cells with a rear interface passivation strategy are studied and characterized. The rear passivation is achieved using an Al2O3 nanopatterned point structure. Using the cell results, photoluminescence measurements, and detailed optical simulations based on the experimental results, it is shown that by including the nanopatterned point contact structure, the interface defect concentration lowers, which ultimately leads to an increase of solar cell electrical performance mostly by increase of the open circuit voltage. Gains to the short circuit current are distributed between an increased rear optical reflection and also due to electrical effects. The approach of mixing several techniques allows us to make a discussion considering the different passivation gains, which has not been done in detail in previous works. A solar cell with a nanopatterned rear contact and a 350 nm thick CIGS absorber provides an average power conversion efficiency close to 10%.
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| 23. |
- Salomé, Pedro M. P., et al.
(författare)
-
Secondary crystalline phases identification in CuZnSnSe thin films : contributions from Raman scattering and photoluminescence
- 2014
-
Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 49:21, s. 7425-7436
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we present the Raman peak positions of the quaternary pure selenide compound CuZnSnSe (CZTSe) and related secondary phases that were grown and studied under the same conditions. A vast discussion about the position of the X-ray diffraction (XRD) reflections of these compounds is presented. It is known that by using XRD only, CZTSe can be identified but nothing can be said about the presence of some secondary phases. Thin films of CZTSe, CuSnSe, ZnSe, SnSe, SnSe, MoSe and a-Se were grown, which allowed their investigation by Raman spectroscopy (RS). Here we present all the Raman spectra of these phases and discuss the similarities with the spectra of CZTSe. The effective analysis depth for the common back-scattering geometry commonly used in RS measurements, as well as the laser penetration depth for photoluminescence (PL) were estimated for different wavelength values. The observed asymmetric PL band on a CZTSe film is compatible with the presence of CZTSe single-phase and is discussed in the scope of the fluctuating potentials' model. The estimated bandgap energy is close to the values obtained from absorption measurements. In general, the phase identification of CZTSe benefits from the contributions of RS and PL along with the XRD discussion.
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| 24. |
- Alberto, Helena, V, et al.
(författare)
-
Characterization of the Interfacial Defect Layer in Chalcopyrite Solar Cells by Depth-Resolved Muon Spin Spectroscopy
- 2022
-
Ingår i: Advanced Materials Interfaces. - : John Wiley & Sons. - 2196-7350. ; 9:19
-
Tidskriftsartikel (refereegranskat)abstract
- As devices become smaller and more complex, the interfaces between adjacent materials become increasingly important and are often critical to device performance. An important research goal is to improve the interface between the absorber and the window layer by inserting buffer layers to adjust the transition. Depth-resolved studies are key for a fundamental understanding of the interface. In the present experiment, the interface between the chalcopyrite Cu(In,Ga)Se-2 absorber and various buffer layers are investigated using low-energy muon spin rotation (mu SR) spectroscopy. Depth resolution in the nm range is achieved by implanting the muons with different energies so that they stop at different depths in the sample. Near the interface, a region about 50 nm wide is detected where the lattice is more distorted than further inside the absorber. The distortion is attributed to the long-range strain field caused by defects. These measurements allow a quantification of the corresponding passivation effect of the buffer layer. Bath-deposited cadmium sulfide provides the best defect passivation in the near interface region, in contrast to the dry-deposited oxides, which have a much smaller effect. The experiment demonstrates the great potential of low energy mu SR spectroscopy for microscopic interfacial studies of multilayer systems.
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| 25. |
- Cunha, Jose M. V., et al.
(författare)
-
High-Performance and Industrially Viable Nanostructured SiOx Layers for Interface Passivation in Thin Film Solar Cells
- 2021
-
Ingår i: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; 5:3
-
Tidskriftsartikel (refereegranskat)abstract
- Herein, it is demonstrated, by using industrial techniques, that a passivation layer with nanocontacts based on silicon oxide (SiOx) leads to significant improvements in the optoelectronical performance of ultrathin Cu(In,Ga)Se-2 (CIGS) solar cells. Two approaches are applied for contact patterning of the passivation layer: point contacts and line contacts. For two CIGS growth conditions, 550 and 500 degrees C, the SiOx passivation layer demonstrates positive passivation properties, which are supported by electrical simulations. Such positive effects lead to an increase in the light to power conversion efficiency value of 2.6% (absolute value) for passivated devices compared with a nonpassivated reference device. Strikingly, both passivation architectures present similar efficiency values. However, there is a trade-off between passivation effect and charge extraction, as demonstrated by the trade-off between open-circuit voltage (V-oc) and short-circuit current density (J(sc)) compared with fill factor (FF). For the first time, a fully industrial upscalable process combining SiOx as rear passivation layer deposited by chemical vapor deposition, with photolithography for line contacts, yields promising results toward high-performance and low-cost ultrathin CIGS solar cells with champion devices reaching efficiency values of 12%, demonstrating the potential of SiOx as a passivation material for energy conversion devices.
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| 26. |
- Fjällström, Viktor, et al.
(författare)
-
Potential-Induced Degradation of CuIn1-xGaxSe2 Thin Film Solar Cells
- 2013
-
Ingår i: IEEE Journal of Photovoltaics. - 2156-3381. ; 3:3, s. 1090-1094
-
Tidskriftsartikel (refereegranskat)abstract
- The use of Na-free or low Na content glass substrates is observed to enhance the resiliency to potential-induced degradation, as compared with glass substrates with high Na content, such as soda lime glass (SLG). The results from stress tests in this study suggest that degradation caused by a combination of heat and bias across the SLG substrate is linked to increased Na concentration in the CdS and Cu(In,Ga)Se-2 (CIGS) layers in CIGS-based solar cells. The degradation during the bias stress is dramatic. The efficiency drops to close to 0% after 50 h of stressing. On the other hand, cells on Na-free and low Na content substrates exhibited virtually no efficiency degradation. The degraded cells showed partial recovery by resting at room temperature without bias; thus, the degradation is nonpermanent and may be due to Na migration and accumulation rather than chemical reaction.
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| 27. |
- Kovacic, M., et al.
(författare)
-
Light management design in ultra-thin chalcopyrite photovoltaic devices by employing optical modelling
- 2019
-
Ingår i: Solar Energy Materials and Solar Cells. - : ELSEVIER. - 0927-0248 .- 1879-3398. ; 200
-
Tidskriftsartikel (refereegranskat)abstract
- In ultra-thin chalcopyrite solar cells and photovoltaic modules, efficient light management is required to increase the photocurrent and to gain in conversion efficiency. In this work we employ optical modelling to investigate different optical approaches and quantify their potential improvements in the short-circuit current density of Cu (In, Ga)Se-2 (CIGS) devices. For structures with an ultra-thin (500 nm) CIGS absorber, we study the improvements related to the introduction of (i) highly reflective metal back reflectors, (ii) internal nano-textures applied to the substrate and (iii) external micro-textures by using a light management foil. In the analysis we use CIGS devices in a PV module configuration, thus, solar cell structure including encapsulation and front glass. A thin Al2O3 layer was considered in the structure at the rear side of CIGS for passivation and diffusion barrier for metal reflectors. We show that not any individual aforementioned approach is sufficient to compensate for the short circuit drop related to ultra-thin absorber, but a combination of a highly reflective back contact and textures (internal or external) is needed to obtain and also exceed the short-circuit current density of a thick (1800 nm) CIGS absorber.
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| 28. |
- Kovacic, M., et al.
(författare)
-
Modelling Supported Design of Light Management Structures in Ultra-Thin Cigs Photovoltaic Devices
- 2019
-
Ingår i: Informacije midem. - : Drustvo MIDEM. - 0352-9045. ; 49:3, s. 183-190
-
Tidskriftsartikel (refereegranskat)abstract
- Chalcopyrite solar cells exhibit one of the highest conversion efficiencies among thin-film solar cell technologies (> 23.3%), however a considerably thick absorber >= 1.8 mu m is required for an efficient absorption of the long-wavelength light and collection of charge carriers. In order to minimize the material consumption and to accelerate the fabrication process, further thinning down of the absorber layer is important. Using a thin absorber layer results in a highly reduced photocurrent density and to compensate for it an effective light management needs to be introduced. Experimentally supported, advanced optical simulations in a PV module configuration, i.e. solar cell structure including the encapsulation and front glass are employed to design solutions to increase the short current density of devices with ultra-thin (500 nm) absorbers. In particular (i) highly reflective metal back reflector (BR), (ii) internal nano-textures and (iii) external textures by applying a light management (LM) foil are investigated by simulations. Experimental verification of simulation results is presented for the external texture case. In the scope of this contribution we show that any individual aforementioned approach is not sufficient to compensate for the short circuit current drop of the thin CIGS, but only a combination of highly reflective back contact and introduction of textures (internal or external) is able to compensate and also to exceed (by more than 5 % for internal texture) photocurrent density of a thick (1800 nm) CIGS absorber.
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| 29. |
- Monteiro, Margarida, et al.
(författare)
-
X-ray Photoelectron Spectroscopy for Studying Passivation Architectures of Cu(In,Ga)Se-2 Cells
- 2021
-
Ingår i: 2021 IEEE 48th Photovoltaic Specialists Conference (PVSC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665419222 ; , s. 890-892
-
Konferensbidrag (refereegranskat)abstract
- Optoelectronic devices are susceptible to interface recombination, which can have a detrimental impact on their performance. Therefore, there is an urgent need for tailored passivation strategies to reach a technological boost. In this contribution, two architectures based on passivated Cu(In, Ga)Se-2 solar cells are analyzed with X-ray photoelectron spectroscopy (XPS): one based on rear passivation with gold nanoparticle aggregates, and the other with Al2O3 as a front passivation layer. It is demonstrated that XPS can assist in the understanding of passivated devices from a chemical point of view, comprehend their limitations and push forward the development of future devices.
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| 30. |
- Oliveira, Kevin, et al.
(författare)
-
SiO$_x$ Patterned Based Substrates Implemented in Cu(In,Ga)Se$_2$ Ultrathin Solar Cells : Optimum Thickness
- 2022
-
Ingår i: IEEE Journal of Photovoltaics. - : Institute of Electrical and Electronics Engineers (IEEE). - 2156-3381 .- 2156-3403. ; 12:4, s. 954-961
-
Tidskriftsartikel (refereegranskat)abstract
- Interface recombination in sub-mu m optoelectronics has a major detrimental impact on devices' performance, showing the need for tailored passivation strategies to reach a technological boost. In this article, SiO$_x$ passivation based substrates were developed and integrated into ultrathin Cu(In,Ga)Se$_2$ (CIGS) solar cells. This article aims to understand the impact of a passivation strategy, which uses several SiO$_x$ layer thicknesses (3, 8, and 25 nm) integrated into high-performance substrates (HPS). The experimental study is complemented with 3-D lumerical finite-difference time-domain and 2-D Silvaco ATLAS optical and electrical simulations, respectively, to perform a decoupling of optical and electronic gains, allowing for a deep discussion on the impact of the SiO$_x$ layer thickness in the CIGS solar cell performance. This article shows that as the passivation layer thickness increases, a rise in parasitic losses is observed. Hence, a balance between beneficial passivation and optical effects with harmful architectural constraints defines a threshold thickness to attain the best solar cell performance. Analyzing their electrical parameters, the 8-nm novel SiO$_x$ based substrate achieved a light to power conversion efficiency value of 13.2%, a 1.3% absolute improvement over the conventional Mo substrate (without SiO$_x$).
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| 31. |
- Oliveira, Kevin, et al.
(författare)
-
SiOx patterned based substrates implemented in Cu(In,Ga)Se-2 ultrathin solar cells : optimum thickness
- 2021
-
Ingår i: 2021 IEEE 48th Photovoltaic Specialists Conference (PVSC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665419222 ; , s. 928-930
-
Konferensbidrag (refereegranskat)abstract
- Interface recombination in sub-mu m optoelectronic devices has a major harmful impact in devices performance, showing the need for tailored passivation strategies in order to reach a technological boost. In this work, SiOx based substrates were developed and integrated in ultrathin CIGS solar cells. This study aims at understanding the impact of several SiOx layer thicknesses (3, 8 and 25 nm) when this material is used as a passivation layer. Analysing their electrical parameters, the 8 nm novel SiOx based substrates achieved light to power conversion efficiency values up to 13.2 %, a 1.3 % absolute improvement over the conventional substrate (without SiOx).
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| 32. |
|
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| 33. |
- Salome, Pedro M. P., et al.
(författare)
-
Cd and Cu Interdiffusion in Cu(In, Ga) Se-2/CdS Hetero-Interfaces
- 2017
-
Ingår i: IEEE Journal of Photovoltaics. - : Institute of Electrical and Electronics Engineers (IEEE). - 2156-3381 .- 2156-3403. ; 7:3, s. 858-863
-
Tidskriftsartikel (refereegranskat)abstract
- We report a detailed characterization of an industrylike prepared Cu(In, Ga) Se-2 (CIGS)/CdS heterojunction by scanning transmission electron microscopy and photoluminescence (PL). Energy dispersive X-ray spectroscopy shows the presence of several regions in the CIGS layer that are Cu deprived and Cd enriched, suggesting the segregation of Cd-Se. Concurrently, the CdS layer shows Cd-deprived regions with the presence of Cu, suggesting a segregation of Cu-S. The two types of segregations are always found together, which, to the best of our knowledge, is observed for the first time. The results indicate that there is a diffusion process that replaces Cu with Cd in the CIGS layer and Cd with Cu in the CdS layer. Using a combinatorial approach, we identified that this effect is independent of focused-ion beam sample preparation and of the transmission electron microscopy grid. Furthermore, PL measurements before and after an HCl etch indicate a lower degree of defects in the postetch sample, compatible with the segregates removal. We hypothesize that Cu2-x Se nanodomains react during the chemical bath process to form these segregates since the chemical reaction that dominates this process is thermodynamically favorable. These results provide important additional information about the formation of the CIGS/CdS interface.
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| 34. |
- Adom, P. K., et al.
(författare)
-
Degree of financialization and energy efficiency in Sub-Saharan Africa: do institutions matter?
- 2020
-
Ingår i: Financial Innovation. - : Springer Science and Business Media LLC. - 2199-4730. ; 6:1
-
Tidskriftsartikel (refereegranskat)abstract
- The United Nations Sustainable Development Goal 7 emphasizes the need for economies around the world to double their efforts in energy efficiency improvements. This is because improvements in energy efficiency can trigger economic growth and considered as one of the 'green' growth strategies due to its carbon free content. To this end, some empirical studies have investigated the nexus between economic growth and energy efficiency, but the effects of the latter on financial indicators have not been sufficiently studied in the literature, at least in developing economies like Africa. This study examines the effect of energy efficiency improvements on commercial bank profitability under different political regimes (i.e., autocratic and democratic political regimes); something previous literature had neglected. The study uses panel data, consisting of 43 African countries and the simultaneous System Generalized Method of Moments. We found that energy efficiency improvement is more likely to induce higher bank profitability in political institutions with the characteristics of centralization of power compared with those with decentralization of power. Furthermore, for the banking sector, the findings suggest that energy utilization behavior of clients should be included in the loan or credit valuation process. For the government, the agenda of energy efficiency should be aggressively pursued while taking cognizance of creating a political environment that weans itself from a 'grandfathering' behavior.
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| 35. |
- Alonso-Blanco, Carlos, et al.
(författare)
-
1,135 Genomes Reveal the Global Pattern of Polymorphism in Arabidopsis thaliana
- 2016
-
Ingår i: Cell. - : Elsevier. - 0092-8674 .- 1097-4172. ; 166:2, s. 481-491
-
Tidskriftsartikel (refereegranskat)abstract
- Arabidopsis thaliana serves as a model organism for the study of fundamental physiological, cellular, and molecular processes. It has also greatly advanced our understanding of intraspecific genome variation. We present a detailed map of variation in 1,135 high-quality re-sequenced natural inbred lines representing the native Eurasian and North African range and recently colonized North America. We identify relict populations that continue to inhabit ancestral habitats, primarily in the Iberian Peninsula. They have mixed with a lineage that has spread to northern latitudes from an unknown glacial refugium and is now found in a much broader spectrum of habitats. Insights into the history of the species and the fine-scale distribution of genetic diversity provide the basis for full exploitation of A. thaliana natural variation through integration of genomes and epigenomes with molecular and non-molecular phenotypes.
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| 36. |
- Bose, Sourav, et al.
(författare)
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Optical Lithography Patterning of SiO2 Layers for Interface Passivation of Thin Film Solar Cells
- 2018
-
Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 2:12
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrathin Cu(In,Ga)Se-2 solar cells are a promising way to reduce costs and to increase the electrical performance of thin film solar cells. An optical lithography process that can produce sub-micrometer contacts in a SiO2 passivation layer at the CIGS rear contact is developed in this work. Furthermore, an optimization of the patterning dimensions reveals constrains over the features sizes. High passivation areas of the rear contact are needed to passivate the CIGS interface so that high performing solar cells can be obtained. However, these dimensions should not be achieved by using long distances between the contacts as they lead to poor electrical performance due to poor carrier extraction. This study expands the choice of passivation materials already known for ultrathin solar cells and its fabrication techniques.
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| 37. |
- Brennich, Martha, et al.
(författare)
-
Nanoparticle Characterization Methods : Applications of Synchrotron and Neutron Radiation
- 2016
-
Ingår i: Pharmaceutical Nanotechnology. - Weinheim, Germany : John Wiley & Sons. - 9783527340545 - 9783527800681 ; , s. 157-174
-
Bokkapitel (refereegranskat)abstract
- The characterization of materials at the atomic-, nano-, and microscales is of crucial importance in understanding and then tailoring their macroscale properties and function for end-use applications and for effective modern cradle-to-reuse materials cycling. Synchrotron light, as well as the complementary neutron beams, offer exquisite microscopy probes to look into the heart of materials. This chapter presents some examples of pharma-oriented nanoparticle characterization highlighting the possibilities of synchrotron light and neutron beams. Small-angle X-ray scattering (SAXS) is a well-established technique to probe nanoscale structures. SAXS can also deliver valuable information on the structure of self-assembled nanovectors, such as liposomes, which are recognized as efficient platforms for drug delivery. Future developments for neutron characterization will be driven in parallel with instrumental developments at existing sources and future facilities such as the European Spallation Source (ESS) being built in Sweden.
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| 38. |
- Cunha, Jose M., V, et al.
(författare)
-
Decoupling of Optical and Electrical Properties of Rear Contact CIGS Solar Cells
- 2019
-
Ingår i: IEEE Journal of Photovoltaics. - : Institute of Electrical and Electronics Engineers (IEEE). - 2156-3381 .- 2156-3403. ; 9:6, s. 1857-1862
-
Tidskriftsartikel (refereegranskat)abstract
- A novel architecture that comprises rear interface passivation and increased rear optical reflection is presented with the following advantages: i) enhanced optical reflection is achieved by the deposition of a metallic layer over the Mo rear contact; ii) improved interface qualitywithCIGS by adding a sputteredAl 2O 3 layer over the metallic layer; and, iii) optimal ohmic electrical contact ensured by rear-openings refilling with a second layer of Mo as generally observed from the growth of CIGS on Mo. Hence, a decoupling between the electrical function and the optical purpose of the rear substrate is achieved. We present in detail the manufacturing procedure of such type of architecture together with its benefits and caveats. A preliminary analysis showing an architecture proof-of-concept is presented and discussed.
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| 39. |
- Cunha, José M. V., et al.
(författare)
-
Understanding the AC Equivalent Circuit Response of Ultrathin Cu(In,Ga)Se2 Solar Cells
- 2019
-
Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 9:5, s. 1442-1448
-
Tidskriftsartikel (refereegranskat)abstract
- This paper aims to study the ac electrical response of standard-thick, ultrathin, and passivated ultrathin Cu(In,Ga)Se 2 (CIGS) solar cells. Ultrathin CIGS is desired to reduce production costs of CIGS solar cells. Equivalent circuits for modeling the behavior of each type of solar cells in ac regime are based on admittance measurements. It is of the utmost importance to understand the ac electrical behavior of each device, as the electrical behavior of ultrathin and passivated ultrathin CIGS devices is yet to be fully understood. The analysis shows a simpler ac equivalent circuit for the ultrathin device without passivation layer, which might be explained by the lowered bulk recombination for thin-film CIGS solar cells when compared with reference thick ones. Moreover, it is observed an increase in shunt resistance for the passivated ultrathin device, which strengthens the importance of passivation for shunts mitigation when compared with unpassivated devices.
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| 40. |
- Diener, Johanna, et al.
(författare)
-
Epigenetic control of melanoma cell invasiveness by the stem cell factor SALL4
- 2021
-
Ingår i: Nature Communications. - : Nature Portfolio. - 2041-1723. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- Melanoma cells rely on developmental programs during tumor initiation and progression. Here we show that the embryonic stem cell (ESC) factor Sall4 is re-expressed in the Tyr::Nras(Q61K); Cdkn2a(-/-) melanoma model and that its expression is necessary for primary melanoma formation. Surprisingly, while Sall4 loss prevents tumor formation, it promotes micrometastases to distant organs in this melanoma-prone mouse model. Transcriptional profiling and in vitro assays using human melanoma cells demonstrate that SALL4 loss induces a phenotype switch and the acquisition of an invasive phenotype. We show that SALL4 negatively regulates invasiveness through interaction with the histone deacetylase (HDAC) 2 and direct co-binding to a set of invasiveness genes. Consequently, SALL4 knock down, as well as HDAC inhibition, promote the expression of an invasive signature, while inhibition of histone acetylation partially reverts the invasiveness program induced by SALL4 loss. Thus, SALL4 appears to regulate phenotype switching in melanoma through an HDAC2-mediated mechanism. Melanoma cells can switch between proliferative and invasive phenotypes. Here the authors show that the embryonic stem cell factor Sall4 is a negative regulator of melanoma phenotype switching where its loss leads to the acquisition of an invasive phenotype, due to derepression of invasiveness genes.
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| 41. |
- Edoff, Marika, 1965-, et al.
(författare)
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Ultrathin CIGS Solar Cells with Passivated and Highly Reflective Back Contacts – : Results from the ARCIGS-M Consortium
- 2019
-
Ingår i: Proceedings of 36th European Photovoltaic Solar Energy Conference and Exhibition. ; , s. 597-600
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this work, we report results from the EU-funded project ARCIGS-M. The project started in 2016 and aims to reduce the use of indium and gallium by enabling the use of very thin Cu(In,Ga)Se2 (CIGS) layers while retaining high efficiency and developing innovative low-cost steel substrates as alternatives to glass. In the project, reflective layers containing TCO´s and silver have successfully been used to enhance the reflective properties of the rear contact. In addition, passivation layers based on alumina (Al2O3) deposited by atomic layer deposition (ALD) have been found to yield good passivation of the rear contact. Since the alumina layers are dielectric, perforation of these layers is necessary to provide adequate contacting. The design of the perforation patterns has been investigated by a combination of modeling and experimental verification by electron beam lithography. In parallel a nano-imprint lithography (NIL) process is further developed for scale-up and application in prototype modules. Advanced optoelectrical characterization supported by modeling is used to fill in the missing gaps in optical and electrical properties, regarding CIGS, interfaces and back contact materials.
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| 42. |
- Egecioglu, Emil, 1977, et al.
(författare)
-
Ghrelin increases intake of rewarding food in rodents
- 2010
-
Ingår i: Addiction Biology. - : Wiley. - 1355-6215 .- 1369-1600. ; 15:3, s. 304-311
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated whether ghrelin action at the level of the ventral tegmental area (VTA), a key node in the mesolimbic reward system, is important for the rewarding and motivational aspects of the consumption of rewarding/palatable food. Mice with a disrupted gene encoding the ghrelin receptor (GHS-R1A) and rats treated peripherally with a GHS-R1A antagonist both show suppressed intake of rewarding food in a free choice (chow/rewarding food) paradigm. Moreover, accumbal dopamine release induced by rewarding food was absent in GHS-R1A knockout mice. Acute bilateral intra-VTA administration of ghrelin increased 1-hour consumption of rewarding food but not standard chow. In comparison with sham rats, VTA-lesioned rats had normal intracerebroventricular ghrelin-induced chow intake, although both intake of and time spent exploring rewarding food was decreased. Finally, the ability of rewarding food to condition a place preference was suppressed by the GHS-R1A antagonist in rats. Our data support the hypothesis that central ghrelin signaling at the level of the VTA is important for the incentive value of rewarding food.
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| 43. |
- Ferreira da Silva, Eduardo, et al.
(författare)
-
Heavy metal pollution downstream the abandoned Coval da Mó mine (Portugal) and associated effects on epilithic diatom communities
- 2009
-
Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 407:21, s. 5620-5636
-
Tidskriftsartikel (refereegranskat)abstract
- This study examined trace-element concentrations in 39 sediment samples collected in the vicinity of the abandoned Coval da Mó mine, and evaluated the anthropogenic contaminant effects and other environmental variables in the taxonomic composition, structure and morphological changes of benthic diatom communities.The results show the existence of extremely high contamination in Pb, Zn and Cd (the mean values exceed the background values 376, 96 and 19 times, respectively) on the first 2.5 km in the water flow direction. Also Co, Cu, Mn and Ni are present in high concentrations. Dilution by relatively uncontaminated sediment reduces metal concentrations downstream, but Zn concentrations increase downstream Fílvida stream, as a result of several factors such as sewage and agriculture.To evaluate the biological effects caused by Pb, Cd and Zn, three sites were selected. In the stressed environment, near the mining area (C232), diatoms were extremely rare, however there was a slight recovery at site C79 located 2 km downstream. Fragilaria capucina var. rumpens, Fragilaria cf. crotonensis and Achnanthidium minutissimum showed abnormal valves which may be related to high levels of metals.Six km downstream, in Fílvida stream (C85), an increase in species richness and diversity was registered while the relative percentage of valve teratologies was lower. In the absence of OM, nutrients and low pH the diatom community patterns must be attributed to the metal concentration at some sites. Considering that community diversity can be affected by abiotic and biotic variables and valve deformations are caused by a small number of variables, basically metals, and acid conditions, we consider the presence of teratologies as an indication of the presence of metals.
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| 44. |
- Fjällström, Viktor, et al.
(författare)
-
Recovery After Potential-Induced Degradation of CuIn1-xGaxSe2 Solar Cells With CdS and Zn(O,S) Buffer Layers
- 2015
-
Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 5:2, s. 664-669
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Tidskriftsartikel (refereegranskat)abstract
- This study deals with potential-induced degradation (PID) of Cu(In,Ga)Se-2-based solar cells and different approaches to subsequent recovery of efficiency. Three different recovery methods were studied: 1) etch recovery, 2) accelerated recovery, and 3) unaccelerated recovery. After being completely degraded, the solar cells with CdS buffer layers recovered their efficiencies at different rates, depending on the method which was used. On the other hand, if Zn(O,S) was used as a buffer layer instead of CdS, the recovery rate was close to zero. The buffer layer type clearly influenced the sodium distribution during PID stressing and recovery, as well as the possibilities for recovery of the electrical performance.
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| 45. |
- Frisk, Christopher, 1985-, et al.
(författare)
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Optimizing Ga-profiles for highly efficient Cu(In,Ga)Se2 thin film solar cells in simple and complex defect models
- 2014
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 47:48, s. 485104-
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Tidskriftsartikel (refereegranskat)abstract
- Highly efficient Cu(In,Ga)(S,Se)2 photovoltaic thin film solar cells often have a compositional variation of Ga to In in the absorber layer, here described as a Ga-profile. In this work we have studied the role of Ga-profiles in four different models, based on input data from electrical and optical characterizations of an in-house state-of-the-art Cu(In,Ga)Se2 (CIGS) solar cell with power conversion efficiency above 19 %. A simple defect model with mid-gap defects in the absorber layer was compared with models with Ga-dependent defect concentrations and amphoteric defects. In these models optimized single-graded Ga-profiles have been compared with optimized double-graded Ga-profiles. It was found that the defect concentration for effective Shockley-Read-Hall recombination is low for high efficiency CIGS devices and that the doping concentration of the absorber layer, chosen according to the defect model, is paramount when optimizing Ga-profiles. For optimized single-graded Ga-profiles the simulated power conversion efficiency, depending on the model, is 20.5-20.8 %, and the equivalent double-graded Ga-profiles yield 20.6-21.4 %, indicating that the bandgap engineering of the CIGS device structure can lead to improvements in efficiency. Apart from the effects of increased doping in the complex defect models, the results are similar when comparing the complex defect models to the simple defect models.
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| 46. |
- Hultqvist, Adam, et al.
(författare)
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Performance of Cu(In,Ga)Se-2 solar cells using nominally alkali free glass substrates with varying coefficient of thermal expansion
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 114:9, s. 094501-
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Tidskriftsartikel (refereegranskat)abstract
- In this report, Cu(In,Ga)Se-2, CIGS, solar cell devices have been fabricated on nominally alkali free glasses with varying coefficients of thermal expansion (CTE) from 50 to 95* 10(-7)/degrees C. A layer of NaF deposited on top of the Mo was used to provide Na to the CIGS film. Increasing the glass CTE leads to a change of stress state of the solar cell stack as evidenced by measured changes of stress state of the Mo layer after CIGS deposition. The open circuit voltage, the short circuit current density, and the fill factors, for solar cells made on the various substrates, are all found to increase with CTE to a certain point. The median energy conversion efficiency values for 32 solar cells increases from 14.6% to the lowest CTE glass to 16.5% and 16.6%, respectively, for the two highest CTE glasses, which have CTE values closest to that of the soda lime glass. This is only slightly lower than the 17.0% median of soda lime glass reference devices. We propose a model where an increased defect density in the CIGS layer caused by thermal mismatch during cool-down is responsible for the lower efficiency for the low CTE glass substrates.
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| 47. |
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| 48. |
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| 49. |
- Kawakatsu, Taiji, et al.
(författare)
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Epigenomic Diversity in a Global Collection of Arabidopsis thaliana Accessions
- 2016
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Ingår i: Cell. - : Elsevier. - 0092-8674 .- 1097-4172. ; 166:2, s. 492-505
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Tidskriftsartikel (refereegranskat)abstract
- The epigenome orchestrates genome accessibility, functionality, and three-dimensional structure. Because epigenetic variation can impact transcription and thus phenotypes, it may contribute to adaptation. Here, we report 1,107 high-quality single-base resolution methylomes and 1,203 transcriptomes from the 1001 Genomes collection of Arabidopsis thaliana. Although the genetic basis of methylation variation is highly complex, geographic origin is a major predictor of genome-wide DNA methylation levels and of altered gene expression caused by epialleles. Comparison to cistrome and epicistrome datasets identifies associations between transcription factor binding sites, methylation, nucleotide variation, and co-expression modules. Physical maps for nine of the most diverse genomes reveal how transposons and other structural variants shape the epigenome, with dramatic effects on immunity genes. The 1001 Epigenomes Project provides a comprehensive resource for understanding how variation in DNA methylation contributes to molecular and non-molecular phenotypes in natural populations of the most studied model plant.
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| 50. |
- Lontchi, Jackson, et al.
(författare)
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Optimization of Back Contact Grid Size in Al2O3-Rear-Passivated Ultrathin CIGS PV Cells by 2-D Simulations
- 2020
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Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 10:6, s. 1908-1917
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Tidskriftsartikel (refereegranskat)abstract
- We present a simulation strategy using ATLAS-2D to optimize the back-contact hole grid (i.e., size and pitch of openings) of the Al 2 O 3 -rear-passivation layer in ultrathin Cu(In,Ga)Se 2 photovoltaic cells. We first discuss and compare our simulation model with a series of experimental nonpassivated and passivated cells to decouple the crucial passivation parameters. The simulation results follow the experimental trends, highlighting the beneficial effects of the passivation on the cell performances. Furthermore, it stresses the influence of the passivation quality at the Al 2 O 3 /Cu(In,Ga)Se 2 (CIGS) interface and of the contact resistance at the Mo/CIGS interface within the openings. Further simulations quantify significant improvements in short-circuit current and open-circuit voltage for different sizes of openings in the Al 2 O 3 layer, relative to an excellent passivation quality (i.e., high density of negative charges in the passivation layer). However, a degradation is predicted for a poor passivation (i.e., low density of such charges) or a high contact resistance. Consequently, we point out an optimum in efficiency when varying the opening widths at fixed hole-pitch and fixed contact resistance. At equivalent contact resistance, simulations predict that the sizes of the pitch and openings can be increased without optimal performance losses when maintaining a width to pitch ratio around 0.2. This simulation trends have been confirmed by a series of experiments, indicating that it is crucial to care about the dimensions of the opening grid and the contact resistance of passivated cells. These simulation results provide significant insights for optimal cell design and characterizations of passivated UT-CIGS PV cells.
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