| 1. |
- 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
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Ingår i: Proceedings of 36th European Photovoltaic Solar Energy Conference and Exhibition. ; , s. 597-600
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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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| 2. |
- Kotipalli, Ratan, et al.
(författare)
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Addressing the impact of rear surface passivation mechanisms on ultra-thin Cu(In,Ga)Se2 solar cell performances using SCAPS 1-D model
- 2017
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Ingår i: Solar Energy. - : Elsevier. - 0038-092X .- 1471-1257. ; 157, s. 603-613
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Tidskriftsartikel (refereegranskat)abstract
- We present a (1-D) SCAPS device model to address the following: (i) the surface passivation mechanisms (i.e.field-effect and chemical), (ii) their impact on the CIGS solar cell performance for varying CIGS absorberthickness, (iii) the importance of fixed charge type (+/−) and densities of fixed and interface trap charges, and(iv) the reasons for discrete gains in the experimental cell efficiencies (previously reported) for varying CIGSabsorber thickness. First, to obtain a reliable device model, the proposed set of parameters is validated for bothfield-effect (due to fixed charges) and chemical passivation (due to interface traps) using a simple M-I-S teststructure and experimentally extracted values (previously reported) into the SCAPS simulator. Next, we providefigures of merits without any significant loss in the solar cell performances for minimum net −Qf and maximumacceptable limit for Dit, found to be ∼5 × 1012 cm−2 and ∼1 × 1013 cm−2 eV−1 respectively. We next showthat the influence of negative fixed charges in the rear passivation layer (i.e. field-effect passivation) is morepredominant than that of the positive fixed charges (i.e. counter-field effect) especially while considering ultrathin(<0.5 μm) absorber layers. Furthermore, we show the importance of rear reflectance on the short-circuitphotocurrent densities while scaling down the CIGS absorber layers below 0.5 μm under interface chemical andfield-effect passivation mechanisms. Finally, we provide the optimal rear passivation layer parameters for efficienciesgreater than 20% with ultra-thin CIGS absorber thickness (<0.5 μm). Based on these simulation results,we confirm that a negatively charged rear surface passivation with nano-point contact approach is efficient forthe enhancement of cell performances, especially while scaling down the absorber thickness below 0.5 μm.
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| 3. |
- Kotipalli, Ratan, et al.
(författare)
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Influence of Ga/(Ga plus In) grading on deep-defect states of Cu(In, Ga)Se-2 solar cells
- 2015
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Ingår i: Physica Status Solidi. Rapid Research Letters. - : Wiley. - 1862-6254 .- 1862-6270. ; 9:3, s. 157-160
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Tidskriftsartikel (refereegranskat)abstract
- The benefits of gallium (Ga) grading on Cu(In, Ga) Se-2 (CIGS) solar cell performance are demonstrated by comparing with ungraded CIGS cells. Using drive-level capacitance profiling (DLCP) and admittance spectroscopy (AS) analyses, we show the influence of Ga grading on the spatial variation of deep defects, free-carrier densities in the CIGS absorber, and their impact on the cell's open-circuit voltage V-oc. The parameter most constraining the cell's Voc is found to be the deep-defect density close to the space charge region (SCR ). In ungraded devices, high deep-defect concentrations (4.2 x 1016 cm(-3)) were observed near the SCR, offering a source for Shockley Read-Hall recombination, reducing the cell's Voc. In graded devices, the deep-defect densities near the SCR decreased by one order of magnitude (2.5 x 1015 cm(-3)) for back surface graded devices, and almost two orders of magnitude (8.6 x 1014 cm(-3)) for double surface graded devices, enhancing the cell's Voc. In compositionally graded devices, the free-carrier density in the absorber's bulk decreased in tandem with the ratio of gallium to gallium plus indium ratio GGI = Ga/(Ga + In), increasing the activation energy, hindering the ionization of the defect states at room temperature and enhancing their role as recombination centers within the energy band.
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| 4. |
- Poncelet, Olivier, et al.
(författare)
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Optimisation of rear reflectance in ultra-thin CIGS solar cells towards>20% efficiency
- 2017
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Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 146, s. 443-452
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Tidskriftsartikel (refereegranskat)abstract
- In order to decrease their cost and the use of rare metal elements, thin film solar cell thicknesses are con-tinuously reduced at the expense of their efficiency, due to a lack of absorption for long wavelengths.Optimisation of cells rear reflectance (Rb) thus becomes meaningful to provide non-absorbed light a sec-ond chance to be harvested by the active cell layer. In this sense, we present a way to keep the rear reflec-tance in advanced Cu(In, Ga) Se2(CIGS) cell as high as possible while keeping in mind the progressalready done regarding the rear passivation techniques. We show that introducing a stack of thin Al2O3 and aluminium between the CIGS layer and the rear molybdenum electrode increases Rbup to92% in the long wavelength 800–1100 nm range. Several other stacks, using MgF2, SiO2or TiO2, are opti-mised in order to investigate the best trade-off between passivation, material consumption and perfor-mances, resulting in Rbranging from 42% (moderate case) to 99% in the best case. Those CIGS rearinterface reflectance optimisations were performed by using a standard transfer matrix method (TMM)in the long wavelength range. Seven interesting stacks are then analysed for solar cell performances usingSCAPS simulation software to understand the impact of rear reflectance on short circuit current density(Jsc) and eventually on the cell efficiency (g), for ultra-thin CIGS absorber thicknesses (<1 lm). Based onthese results, we propose Rboptimisation to achieve Jsc> 40 mA/cm2and g > 20% with a 500 nm-thickCIGS absorber film using CIGS-Al2O3-Mo stack, where the Al2O3thickness can be chosen in between104 and 139 nm. This way, we can ensure good rear reflectance (Rb= 65%) and reduced interface recom-bination while being industrially feasible with present technologies.
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| 5. |
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| 6. |
- Vermang, Bart, et al.
(författare)
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Highly reflective rear surface passivation design for ultra-thin Cu(In,Ga) Se-2 solar cells
- 2015
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 582, s. 300-303
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Tidskriftsartikel (refereegranskat)abstract
- Al2O3 rear surface passivated ultra-thin Cu(In,Ga)Se-2 (CIGS) solar cells with Mo nano-particles (NPs) as local rear contacts are developed to demonstrate their potential to improve optical confinement in ultra-thin CIGS solar cells. The CIGS absorber layer is 380 nm thick and the Mo NPs are deposited uniformly by an up-scalable technique and have typical diameters of 150 to 200 nm. The Al2O3 layer passivates the CIGS rear surface between the Mo NPs, while the rear CIGS interface in contact with the Mo NP is passivated by [Ga]/([Ga] + [In]) (GGI) grading. It is shown that photon scattering due to the Mo NP contributes to an absolute increase in short circuit current density of 3.4 mA/cm(2); as compared to equivalent CIGS solar cells with a standard back contact.
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