| 1. |
- Bliss, Martin, et al.
(författare)
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Spectral Response Measurements of Perovskite Solar Cells
- 2019
-
Ingår i: IEEE Journal of Photovoltaics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2156-3381 .- 2156-3403. ; 9:1, s. 220-226
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Tidskriftsartikel (refereegranskat)abstract
- A new spectral response (SR) measurement routine is proposed that is universally applicable for all perovskite devices. It is aimed at improving measurement accuracy and repeatability of SR curves and current-voltage curve spectral mismatch factor (MMF) corrections. Frequency response, effects of preconditioning as well as dependency on incident light intensity and voltage load on SR measurements are characterized on two differently structured perovskite device types. It is shown that device preconditioning affects the SR shape, causing errors in spectral MMF corrections of up to 0.8% when using a reference cell with a good spectral match and a class A solar simulator. Wavelength dependent response to incident light intensity and voltage load is observed on both device types, which highlights the need to measure at short-circuit current and maximum power point to correct spectral mismatch. The method with recommendations given ensures that the correct measurement conditions are applied and measurements are corrected for instability in performance.
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| 2. |
- Cunha, Jose M., V, et al.
(författare)
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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
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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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| 3. |
- 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
-
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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| 4. |
- Cunha, José M. V., et al.
(författare)
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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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| 5. |
- Edoff, Marika, 1965-, et al.
(författare)
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High Voc in (Cu,Ag)(In,Ga)Se2 Solar Cells
- 2017
-
Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 7:6, s. 1789-1794
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Tidskriftsartikel (refereegranskat)abstract
- In this contribution, we show that silver substitution for copper in Cu(In,Ga)Se-2 (CIGS) to form (Ag,Cu)(In, Ga)Se-2 (ACIGS) leads to a reduction of the voltage loss expressed as E-g/q-V-oc. This, in turn, leads to higher device efficiencies as compared to similar CIGS devices without Ag. We report V-oc at 814 mV at a conversion efficiency of 21% for our best ACIGS device with 20% of the group I element consisting of silver. Comparing ACIGS and CIGS devices with the same Ga/(Ga+ In) ratio, the ACIGS devices exhibit about 0.05 eV higher bandgap. Alkali postdeposition treatment with KF leads to improvements in efficiency both for CIGS and ACIGS, but we find that the dose of KF needed for optimum device for ACIGS is 10-20% of the dose used for CIGS.
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| 6. |
- Fjällström, Viktor, et al.
(författare)
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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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| 7. |
- Frisk, Christopher, 1985-, et al.
(författare)
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On the extraction of doping concentration from capacitance-voltage : A Cu2ZnSnS4 and ZnS sandwich structure
- 2017
-
Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 7:5, s. 1421-1425
-
Tidskriftsartikel (refereegranskat)abstract
- The capacitance-voltage (C-V) method is frequently used to evaluate the net doping of thin-film solar cells, an important parameter for the function of solar cells. However, complex materials such as kesterites are challenging to characterize. To minimize ambiguity when determining the apparent doping concentration (N-A) of Cu2ZnSnS4 (CZTS), we fabricated and investigated different structures: CZTS/ZnS metal-insulator-semiconductor (MIS) device, stand-alone CZTS and ZnS metal-sandwich structures, and CZTS solar cells. Characterization was carried out by means of admittance spectroscopy (AS) and C-V measurements. ZnS exhibits excellent intrinsic properties, and with the high-quality MIS sample we managed to successfully isolate the capacitive response of the CZTS itself. N-A, as extracted from the MIS structure, is found to be more reliable and four times higher compared with the solar cell, impacting any estimated collection efficiency substantially. Data herein presented also show that CZTS has a substantial low-frequency dispersive capacitance and the extraction of N-A depends on the chosen measurement frequency, symptoms of presence of deep defects. Furthermore, the CZTS/ZnS MIS structure is strongly resilient to leakage currents at both forward and reverse voltage bias where contribution from deep defects is minimized and maximized, respectively.
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| 8. |
- Goffard, Julie, et al.
(författare)
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Light Trapping in Ultrathin CIGS Solar Cells withNanostructured Back Mirrors
- 2017
-
Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 7:5, s. 1433-1441
-
Tidskriftsartikel (refereegranskat)abstract
- Novel architectures for light trapping in ultrathinCu(In,Ga)Se2 (CIGS) solar cells are proposed and numericallyinvestigated. They are composed of a flat CIGS layer withnanostructured back mirrors made of highly reflective metals.Multi-resonant absorption is obtained for two different patternsof nanostructured mirrors. It leads to a dramatic increase in theshort-circuit current predicted for solar cells with very thin CIGSlayers. We analyze the resonance phenomena and the density ofphotogenerated carriers in the absorber. We discuss the impactof the material used for the buffer layer (CdS and ZnS) and theback mirror (Mo, Cu, Au, and Ag). We investigate various CIGSthicknesses from 100 to 500 nm, and we compare our numericalresults with experimental data taken from the literature. Wepredict a short-circuit current of Jsc = 33.6 mA/cm2 for a realisticsolar cell made of a 200-nm-thick CIGS absorber with a coppernanostructured mirror. It opens a way toward ultrathin CIGSsolar cells with potential conversion efficiencies up to 20%.
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| 9. |
- Gouillart, Louis, et al.
(författare)
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Reflective Back Contacts for Ultrathin Cu(In,Ga)Se2-Based Solar Cells
- 2020
-
Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 10:1, s. 250-254
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the development of highly reflective back contacts (RBCs) made of multilayer stacks for ultrathin CIGS solar cells. Two architectures are compared: they are made of a silver mirror coated either with a single layer of In 2 O 3 :Sn (ITO) or with a bilayer of ZnO:Al/ITO. Due to the improvement of CIGS rear reflectance, both back contacts result in a significant external quantum efficiency enhancement, in agreement with optical simulations. However, solar cells fabricated with Ag/ITO back contacts exhibit a strong shunting behavior. The key role of the ZnO:Al layer to control the morphology of the top ITO layer and to avoid silver diffusion through the back contact is highlighted. For a 500-nm-thick CIGS layer, this optimized RBC leads to a best cell with a short-circuit current of 27.8 mA/cm 2 (+2.2 mA/cm 2 as compared to a Mo back contact) and a 12.2%-efficiency (+2.5% absolute).
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| 10. |
- Hultqvist, Adam, et al.
(författare)
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Buffer Layer Point Contacts for CIGS Solar Cells Using Nanosphere Lithography and Atomic Layer Deposition
- 2017
-
Ingår i: IEEE Journal of Photovoltaics. - : Institute of Electrical and Electronics Engineers (IEEE). - 2156-3381 .- 2156-3403. ; 7:1, s. 322-328
-
Tidskriftsartikel (refereegranskat)abstract
- Point contacts provide an interesting approach for reducing the buffer layer/Cu(In, Ga)Se-2 interface recombination that typically limits Cu(In, Ga) Se-2 solar cell performance when nontoxic alternatives to CdS buffer layers are used. In this study, we implement a scheme to create a point contact buffer layer on Cu(In, Ga)Se-2 solar cells using a combination of atomic layer deposition and nanosphere lithography. While we showcase these buffer layers using Al2O3 as the passivating material, ZnO as the conductive material, and a silica nanosphere size of 310 nm in diameter, this scheme is general and could readily be applied for other materials and other sphere sizes. The resulting solar cells with Al2O3 and ZnO point contact buffer layers demonstrate successful application of this scheme, yielding a higher conversion efficiency (6.58 +/- 0.58%) than either of the binary buffer layers Al2O3 (0%) and ZnO (5.15 +/- 0.57%). The improvement over ZnO is mainly due to an increased open circuit voltage, which is an indication of a reduced surface recombination.
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| 11. |
- Larsen, Jes K, et al.
(författare)
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Sulfurization of Co-Evaporated Cu(In,Ga)Se-2 as a Postdeposition Treatment
- 2018
-
Ingår i: IEEE Journal of Photovoltaics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2156-3381 .- 2156-3403. ; 8:2, s. 604-610
-
Tidskriftsartikel (refereegranskat)abstract
- It is investigated if the performance of Cu(In,Ga)Se-2 (CIGSe) solar cells produced by co-evaporation can be improved by surface sulfurization in a postdeposition treatment. The expected benefit would be the formation of a sulfur/selenium gradient resulting in reduced interface recombination and increased open-circuit voltage. In the conditions used here it was, however, found that the reaction of the CIGSe layer in a sulfur environment results in the formation of a CuInS2 (CIS) surface phase containing no or very little selenium and gallium. At the same time, a significant pile up of gallium was observed at the CIGSe/CIS boundary. This surface structure was formed for a wide range of annealing conditions investigated in this paper. Increasing the temperature or extending the time of the dwell stage had a similar effect on the material. The gallium enrichment and CIS surface layer widens the surface bandgap and therefore increases the open-circuit voltage. At the same time, the fill factor is reduced, since the interface layer acts as an electron barrier. Due to the balance of these effects, the conversion efficiency could not be improved.
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| 12. |
- Ledinek, Dorothea, et al.
(författare)
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Rear Contact Passivation for High Bandgap Cu(In,Ga)Se2 Solar Cells With a Flat Ga profile
- 2018
-
Ingår i: IEEE Journal of Photovoltaics. - : Institute of Electrical and Electronics Engineers (IEEE). - 2156-3381 .- 2156-3403. ; 8:3, s. 864-870
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, Cu(In, Ga)Se2 solar cells with a high bandgap (1.31 eV) and a flat Ga profile ([Ga]/([Ga]+[In]) ≈ 0.60) were examined. For absorber layer thicknesses varying from 0.60 to 1.45 μm, the Mo rear contact of one set of samples was passivated with an ultrathin (27 nm) Al2O3 layer with point contact openings, and compared with reference samples where the rear contact remained unpassivated. For the passivated samples, mainly large gains in the short-circuit current led to an up to 21% (relative) higher power conversion efficiency compared with unpassivated cells. The differences in temperature-dependent current voltage behavior between the passivated and the unpassivated samples and the thin and the thick samples can be explained by an oppositely poled secondary photodiode at the rear contact.
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| 13. |
- 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
-
Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 10:6, s. 1908-1917
-
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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| 14. |
- Lopes, Tomas S., et al.
(författare)
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Rear Optical Reflection and Passivation Using a Nanopatterned Metal/Dielectric Structure in Thin-Film Solar Cells
- 2019
-
Ingår i: IEEE Journal of Photovoltaics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2156-3381 .- 2156-3403. ; 9:5, s. 1421-1427
-
Tidskriftsartikel (refereegranskat)abstract
- Currently, one of the main limitations in ultrathin Cu(In,Ga)Se-2 (CIGS) solar cells are the optical losses, since the absorber layer is thinner than the light optical path. Hence, light management, including rear optical reflection, and light trapping is needed. In this paper, we focus on increasing the rear optical reflection. For this, a novel structure based on having a metal interlayer in between the Mo rear contact and the rear passivation layer is presented. In total, eight different metallic interlayers are compared. For the whole series, the passivation layer is aluminum oxide (Al2O3). The interlayers are used to enhance the reflectivity of the rear contact and thereby increasing the amount of light reflected back into the absorber. In order to understand the effects of the interlayer in the solar cell performance both from optical and/or electrical point of view, optical simulations were performed together with fabrication and electrical measurements. Optical simulations results are compared with current density-voltage (J-V) behavior and external quantum efficiency measurements. A detailed comparison between all the interlayers is done, in order to identify the material with the greatest potential to he used as a rear reflective layer for ultrathin CIGS solar cells and to establish fabrication challenges. The Ti-W alloy is a promising a rear reflective layer since it provides solar cells with light to power conversion efficiency values of 9.9%, which is 2.2% (abs) higher than the passivated ultrathin sample and 3.7% (abs) higher than the unpassivated ultrathin reference sample.
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| 15. |
- Luo, Jie, et al.
(författare)
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Improved Photovoltaic Characteristics of Inverted Polymer Solar Cells With Indium-Doped ZnO at Low-Temperature Annealing as Electron-Transport Layer
- 2021
-
Ingår i: IEEE Journal of Photovoltaics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2156-3381 .- 2156-3403. ; 11:2, s. 374-378
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Tidskriftsartikel (refereegranskat)abstract
- For inverted solar cells, UV-socking is usually necessary to improve the photovoltaic performance of the devices. In this article, inverted polymer solar cells with pure and indium-doped ZnO as an electron transport layer were fabricated, and their properties were investigated. We found that the In-doped ZnO-based device has a high power conversion efficiency of 5.99%, and a nearly 40% improvement in comparison with the pure ZnO-based device without the UV treatment. Those investigations of X-ray diffraction, Photoluminescence, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectra show that the doping of indium into the lattice of ZnO can decrease defect states and increase the work function, leading to more efficient electron extraction, and consequently, an enhancement of photovoltaic performance of the device.
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| 16. |
- Molin, Elin, et al.
(författare)
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Experimental yield study of bifacial PV modules in Nordic conditions
- 2018
-
Ingår i: IEEE Journal of Photovoltaics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2156-3381 .- 2156-3403. ; 8:6, s. 1457-1463
-
Tidskriftsartikel (refereegranskat)abstract
- This study reports on the first full-year field study in Sweden using bifacial photovoltaic modules. The two test sites are located on flat roofs with a low albedo of 0.05 in Linköping (58 °N) and were studied from December 2016 to November 2017. Site 1 has monofacial and bifacial modules with a 40° tilt facing south, which is optimal for annual energy yield for monofacial modules at this location. Site 2 has monofacial 40° tilt south-facing modules and bifacial vertical east–west orientated modules. The annual bifacial energy gain (BG E ) was 5% at site 1 and 1% at site 2 for albedo 0.05. The difference in power temperature coefficients between bifacial and monofacial modules was estimated to influence BG E by +0.4 and +0.1 percentage points on site 1 and 2, respectively. A higher albedo could be investigated on a sunny day with fresh snow for the bifacial east–west modules. The specific yield was 7.57 kWh/kW p , which was a yield increase of 48% compared with tar paper at similar solar conditions.
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| 17. |
- Oliveira, Kevin, et al.
(författare)
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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
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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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| 18. |
- Qviller, Atle Jorstad, et al.
(författare)
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Hydrogen Concentration in Photovoltaic a-Si:H Annealed at Different Temperatures Measured by Neutron Reflectometry
- 2018
-
Ingår i: IEEE Journal of Photovoltaics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2156-3381 .- 2156-3403. ; 8:4, s. 1098-1101
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous hydrogenated silicon (a-Si:H) is an important material for surface defect passivation of photovoltaic silicon (Si) wafers in order to reduce their recombination losses. The material is, however, unstable with regard to hydrogen (H) desorption at elevated temperatures, which can be an issue during processing and device manufacturing. In this work, we determine the temperature stability of a-Si:H by structural characterization of a-Si:H/Si bilayers with neutron reflectometry and X-ray reflectometry combined with photoconductance measurements, yielding the minority carrier lifetime. The neutrons are sensitive to light elements such as H, while the X-rays, which are insensitive to the H concentration, provide an independent constraint on the layer structure. It is shown that H desorption takes place at a temperature of approximately T = 425 degrees C, and that the H content and minority carrier lifetimes have a strongly correlated linear relationship, which can be interpreted as one H atom passivating one defect.
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| 19. |
- Ross, Nils, et al.
(författare)
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Selenium Inclusion in Cu2ZnSn(S,Se)(4) Solar Cell Absorber Precursors for Optimized Grain Growth
- 2018
-
Ingår i: IEEE Journal of Photovoltaics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2156-3381 .- 2156-3403. ; 8:4, s. 1132-1141
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Tidskriftsartikel (refereegranskat)abstract
- Cu2ZnSn(S,Se)(4) precursors are fabricated by compound cosputtering from metal sulfide and selenide targets, and annealed in mixed argon, sulfur, and selenium atmosphere at temperatures between 540 and 580 degrees C and at pressures between 24 and 47 kPa. We produce solar cell devices from these absorbers that range from 2.0% to 9.0% power conversion efficiency. We extensively characterize the morphology and elemental composition of the absorbers, and are able to closely relate the annealing conditions, precursor sulfur-selenium content, device performance, and absorber quality. We develop a qualitative model which relates the sulfur-selenium distribution in the precursor and the relative partial pressures of sulfur and selenium during the annealing process to the absorber properties. We show that selenium inclusion in the precursor allows more rapid recrystallization of the absorber at lower temperature. Alternating stacking of sulfur and selenium containing precursor material leads to differential rates of recrystallization, which allows some control over the morphology of the annealed absorber and Zn(S,Se) secondary phase segregation in that absorber. We further show that selenium containing precursors can be used to fabricate the superior devices relative to sulfur-only precursors, when the annealing phase space is subject to severe practical restrictions.
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| 20. |
- Salome, Pedro M. P., et al.
(författare)
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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
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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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| 21. |
- Salome, Pedro M. P., et al.
(författare)
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Incorporation of Na in Cu(In,Ga)Se-2 Thin-Film Solar Cells : A Statistical Comparison Between Na From Soda-Lime Glass and From a Precursor Layer of NaF
- 2014
-
Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 4:6, s. 1659-1664
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Tidskriftsartikel (refereegranskat)abstract
- The presence of Na in Cu(In,Ga)Se-2 layers increases the electrical performance of this type of thin- film solar cell. A detailed comparison of incorporating Na in the CIGS layer by two different methods is performed by evaluating several hundred devices fabricated under similar conditions. The firstmethod is based on the conventionally used Na diffusion from the soda-lime glass substrate, whereas the second method is based on a NaF precursor layer deposited on a Mo- coated alkali- free glass substrate. The sample where Na is introduced by using a NaF precursor layer shows an orientation weighted toward (2 0 4)/(2 2 0) and a net acceptor concentration of 3.4 x 10(16) cm(-3), while SLG shows a (1 1 2) orientation with a 2.9 x 10(16) cm(-3) acceptor concentration. Both sample types show close identical elemental depth profiles, morphology, and electrical performance.
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| 22. |
- 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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| 23. |
- Simchi, H., et al.
(författare)
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Transparent Back Contacts for Superstrate (AG,CU)(IN,GA)SE2 Thin Film Solar Cells
- 2015
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Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 5:1, s. 406-409
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Tidskriftsartikel (refereegranskat)abstract
- Molybdenum oxide (MoO3) and tungsten oxide (WO3) are considered as transparent back contacts for (Ag,Cu)(In,Ga)Se-2 thin film solar cells. MoO3 and WO3 films were deposited by reactive RF sputtering at room temperature in an Ar/O-2 ambient on (Ag,Cu)(In,Ga) Se-2 absorber layers with various Ga/(Ga + In) and Ag/(Ag + Cu) ratios. Determination of the valence band offsets by XPS showed that Ag-alloying of absorber layer changes the energy band alignment at the absorber-back contact interface with MoO3 and WO3 contacts. This produces a primary contact with lower valence band offset compared with Cu(In,Ga) Se-2 counterparts. The effect is less significant in films with Ga > 0.5 and Ag > 0.5 (corresponding to E-g > 1.4 eV) probably due to the different nature of ordered vacancy compounds forming near the surface phases.
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| 24. |
- Szaniawski, Piotr, et al.
(författare)
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A Systematic Study of Light-On-Bias Behavior in Cu(In,Ga)Se2 Solar Cells With Varying Absorber Compositions
- 2017
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Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 7:3, s. 882-891
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Tidskriftsartikel (refereegranskat)abstract
- Light-on-bias effects were investigated in multiple Cu(In, Ga)Se2 solar cells with varying absorber layer compositions. A strong link between deformations caused by red-on-bias treatments in current-voltage (IV ) and capacitance-voltage (CV) characteristics was demonstrated. Similarly to red-on-bias, blue-on-bias leads to a local increase in static negative charge, but in samples with CdS buffers this increase is shifted away from the interface and has no impact on device performance. IV characteristics of samples with Cd-free buffers are not affected by any light-on-bias treatments, suggesting that CdS plays a vital role in the decreased performance after red-on-bias. A statistical approach was used to search for compositional trends in red-on-bias behavior. Deformation factors were defined for IV and CV characteristics before and after the treatment. While there is a strong relationship between the deformations observed in both types of measurements, the degree to which red-on-bias affects IV and CV curves can vary dramatically. These variations cannot be attributed to changes in composition, since no clear compositional trends were found. Rather, other factors related to sample manufacturing and to the buffer layer seem to have major impact on red-on-bias behavior.
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| 25. |
- Szaniawski, Piotr, et al.
(författare)
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Advancing the understanding of reverse breakdown in Cu(In,Ga)Se2 solar cells
- 2017
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Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 7:4, s. 1136-1142
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Tidskriftsartikel (refereegranskat)abstract
- Reverse breakdown is investigated in multiple Cu(In,Ga)Se-2 solar cells with varying buffer layer thicknesses. A method to extract transition voltage, which marks the change of conduction mechanism that leads to electrical breakdown, is described as an alternative to the often less-meaningful breakdown voltage. Transition voltages for samples with CdS and ZnxSn1-xOy buffers are extracted from breakdown measurements performed in darkness and under illumination. The electric field is calculated for ZTO-based samples measured in darkness, and its implications for the energy band structure are examined. Fowler-Nordheim tunneling and Poole-Frenkel conduction are considered as candidates for the main breakdown mechanism in darkness. A model combining the two conduction mechanisms is proposed, and fits for experimental data are presented and discussed. Involvement of defects is debated, and defect-andbreakdown- related phenomena are showcased.
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