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# Highly efficient Cu(In,Ga)Se2 solar cells grown on flexible polymer films

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1] Laboratory for Thin Films and Photovoltaics, Swiss Federal Laboratories for Materials Science and Technology Empa, Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland [2].
(Impact Factor: 36.5). 09/2011; 10(11):857-61. DOI: 10.1038/nmat3122
Source: PubMed

ABSTRACT

Solar cells based on polycrystalline Cu(In,Ga)Se(2) absorber layers have yielded the highest conversion efficiency among all thin-film technologies, and the use of flexible polymer films as substrates offers several advantages in lowering manufacturing costs. However, given that conversion efficiency is crucial for cost-competitiveness, it is necessary to develop devices on flexible substrates that perform as well as those obtained on rigid substrates. Such comparable performance has not previously been achieved, primarily because polymer films require much lower substrate temperatures during absorber deposition, generally resulting in much lower efficiencies. Here we identify a strong composition gradient in the absorber layer as the main reason for inferior performance and show that, by adjusting it appropriately, very high efficiencies can be obtained. This implies that future manufacturing of highly efficient flexible solar cells could lower the cost of solar electricity and thus become a significant branch of the photovoltaic industry.

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Available from: Fabian Pianezzi, Oct 16, 2014
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• "For example, CdS thin films are highly favorable in heterojunction thin-film solar cell applications because of their excellent optical E g , photoconductivity, and high electron affinity (Ferekides and Britt, 1994). CdS is widely used as an n-type window layer in chalcogenide thin-film solar cells, such as CdTe, CIGS, Cu 2 ZnSnS 4 , Cd 1Àx Mg x Te because of its wide E g at room temperature (Britt and Ferekides, 1993; Chirila, 2011; Repins et al., 2008; Kosyachenko et al., 2014; Rejón et al., 2013; Wu, 2004). Of these solar cells, the CdTe solar cell attracts much attention because of its high theoretical conversion efficiency (Eff) of 29% (Green et al., 2013). "
##### Article: Improved performance of CdTe solar cells with CdS treatment
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ABSTRACT: CdTe thin-film solar cells are usually composed of n-CdS/p-CdTe. The treatment of CdS in the magnetron chamber prior to radiofrequency magnetron sputtering of CdTe had a significant effect on the properties of CdTe solar cells. We found that a CdS cooling and reheating process prior to CdTe deposition had a significant effect on the energy conversion efficiency and open circuit voltage of CdTe solar cells. Without cooling and reheating CdS before CdTe deposition, the energy conversion efficiency and open circuit voltage of the CdTe solar cell only reached 12.0 ± 0.5% and 759 ± 1 mV, respectively. However, the energy conversion efficiency and open circuit voltage of the CdTe solar cell with a CdS cooling and reheating process before CdTe deposition were 13.3 ± 0.3% and 828 ± 1 mV, respectively. CdS films after the cooling and reheating process had larger grains, superior crystalline quality, and a higher S/Cd atomic ratio compared with films that did not undergo a CdS cooling and reheating process. CdTe grown on CdS with a cooling and reheating process had the largest grain size after chloride treatment.
Solar Energy 03/2015; 115:603-612. DOI:10.1016/j.solener.2015.02.044 · 3.47 Impact Factor
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• "Because of the complexity of the CIGS structures, the development of an optical simulation technique can give a crucial contribution to the interpretation of numerous quantum efficiency spectra and the resulting J SC values reported for CIGS solar cells [1–36]. Nevertheless, the optical simulation of CIGS solar-cell devices is rather difficult because of (i) the light-scattering effect induced by submicron-size CIGS natural textures and (ii) the continuous variation of the Ga content in the CIGS layer [1] [2] [3] [4] [5] [6] [7] [8]. "
##### Article: Quantitative Assessment of Optical Gain and Loss in Submicron-Textured C u I n 1 − x G a x S e 2 Solar Cells Fabricated by Three-Stage Coevaporation
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ABSTRACT: CuIn${}_{1-x}$Ga${}_{x}$Se${}_{2}$ (CIGS) is an important photovoltaic material, but variations in composition and nanoscale textures that form naturally during processing thwart accurate modeling. The authors develop a general formalism to simulate the charge carrier collection in complex multilayered systems, permitting the calculation of the external quantum efficiency of a thin-film solar cell. For a realistic complicated system they find that the collection efficiency in the CIGS layer is almost 100%, while the light absorption in the 1-\mu${}$m-thick bottom region is negligible.
Physical Review Applied 09/2014; 2(3). DOI:10.1103/PhysRevApplied.2.034012
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• "A Cu(In,Ga)Se 2 (CIGS) is the most promising absorber material among the thin-film solar cells due to its high power conversion efficiency and potential for a low-cost production [1]. The thickness of the CIGS absorber could be reduced to under 1 µm with little efficiency drop because of its high absorption coefficient, so that it decreases the material consumption [2]. "
##### Conference Paper: ZnS buffer layer prepared by sulfurization of sputtered Zn film for Cu(In, Ga)Se2 solar cells
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ABSTRACT: We report on a novel method of a fabrication of a ZnS buffer layer for an application of Cu(In, Ga)Se2 (CIGS) solar cells. The ZnS thin film was prepared by a sulfurization of a sputtered Zn film using a sulfur cracker. The structural and optical properties of the ZnS films and the photovoltaic performance of the ZnS-employed CIGS solar cells were investigated. The thin ZnS film played a sufficient role as a buffer layer achieving the power conversion efficiency of 10.5%.
2013 IEEE 39th Photovoltaic Specialists Conference (PVSC); 06/2013