| 1. |
- Anacleto, Pedro, et al.
(author)
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Precisely nanostructured HfO2 rear passivation layers for ultra-thin Cu(In,Ga)Se-2
- 2022
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In: Progress in Photovoltaics. - : John Wiley & Sons. - 1062-7995 .- 1099-159X. ; 30:11, s. 1289-1297
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Journal article (peer-reviewed)abstract
- The quest for material-efficient Cu(In,Ga)Se-2 (CIGS) solar cells encourages the development of ultra-thin absorbers. Their use reduces material consumption and energy usage during production by increasing the throughput. Thereby, both the bill of materials as well as the energy and capital costs are reduced. However, because thin absorbers are prone to increase back contact recombination, back surface passivation schemes are necessary to reach a similar or higher conversion efficiency than for absorbers with conventional thickness. Here, we investigate nanostructured hafnium oxide (HfO2) rear passivation layers for ultra-thin CIGS solar cells. We fabricate regular arrays of point contacts with 200 nm diameter through HfO2 layers with thicknesses between 7 and 40 nm using electron beam lithography and reactive ion etching. The current-voltage curves of solar cells with a 500 nm thick CIGS absorber layer and the nanostructured passivation layer show improved performance concerning V-oc and J(sc) compared to non-passivated reference devices. Furthermore, external quantum efficiency and optical reflection confirm an effective passivation behavior, with an average efficiency increase of up to 1.2% for the cells with the 40 nm thick HfO2 layer. In addition, simulation work shows that even 40 nm thick HfO2 passivation layers have only a minimal effect on the optical properties of ultra-thin CIGS solar cells, and hence, the photocurrent increase verified experimentally stems from electrical improvements caused by the HfO2 layer passivation effect. We also investigate the impact of ultra-thin (0.3, 0.6, 1.3, and 2.5 nm) non-patterned HfO2 passivation layers on the same type of solar cells. However, these results showed no improvement in solar cell performance, despite an increase in the current density with layer thickness.
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| 2. |
- Edoff, Marika, 1965-, et al.
(author)
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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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In: Proceedings of 36th European Photovoltaic Solar Energy Conference and Exhibition. ; , s. 597-600
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Conference paper (other academic/artistic)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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| 3. |
- Kovacic, Milan, et al.
(author)
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Light Management in Ultra-Thin Cu(In, Ga)Se2 Photovoltaic Devices
- 2019
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In: Proceedings of 36th European Photovoltaic Solar Energy Conference and Exhibition. - 3936338604 ; , s. 654-660
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Conference paper (other academic/artistic)abstract
- Cu(In, Ga)Se2 (CIGS) solar cells exhibit high conversion efficiencies, with a recent record of 23.35 % on the cell level. However, an absorber thickness >1.8 m is required for efficient absorption of long-wavelength light. In order to minimize the material consumption (In, Ga and other elements) and to accelerate the fabrication process, further thinning down of CIGS absorber layer is important. One of the main challenges of ultra-thin absorber devices is to increase light absorption and consequently the photocurrent. We employ advanced optical simulations of ultra-thin (500 nm) CIGS devices in a PV module configuration, thus solar cell structure including encapsulation and front glass. Using simulations, we design and investigate different solutions for increased short circuit current, in particular (i) highly reflective back reflectors (BR), (ii) internal nano-textures and (iii) external textures by applying a light management foil. We show that any single solution (i, ii, iii) is not enough to compensate for the lower photocurrent, when thinning down (1800 nm -> 500 nm) the absorber layer. A combination of properly optimized internal or external textures and highly reflective back reflector is needed to reach, or even exceed (by ~3-5 %), the short circuit current of a standard thick (1800 nm) CIGS module structure.
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| 4. |
- Lontchi, Jackson, et al.
(author)
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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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In: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 10:6, s. 1908-1917
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Journal article (peer-reviewed)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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| 5. |
- Lontchi, Jackson, et al.
(author)
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Ultra-thin CIGS : 2D Modelling and impactful results for optimal cell design and characterizations
- 2020
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In: 2020 47th IEEE Photovoltaic Specialists Conference (PVSC). - 9781728161150 - 9781728161167 ; , s. 699-700
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Conference paper (peer-reviewed)abstract
- We present a 2D model of an Al 2 O 3 -passivated ultrathin Cu(In, Ga)Se 2 photovoltaic cell with rear-contact pattern. Simulation results follow the experimental trends, highlighting the significant effects of the passivation quality and of the Mo/CIGS contact resistance. Improvements in Jsc and Voc are discussed for different sizes of openings, 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. We point out an optimum in efficiency when varying the opening widths at fixed hole-pitch and fixed contact resistance for a width to pitch ratio around 0.2. These simulation results provide significant insights for optimal cell design and characterizations of passivated UT-CIGS PV cells.
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