期刊
PROGRESS IN PHOTOVOLTAICS
卷 25, 期 3, 页码 233-241出版社
WILEY
DOI: 10.1002/pip.2850
关键词
Cu(In,Ga)Se2 solar cells; NIR optical response; Cu deficiency in CIGS
资金
- European Union's Horizon Research and Innovation Programme [641004]
- Swiss State Secretariat for Education, Research and Innovation (SERI) [REF-1131-52107]
- Swiss Federal Office of Energy [SI/501145-01.]
Highly efficient thin film solar cells based on co-evaporated Cu(In,Ga)Se-2 (CIGS) absorbers are typically grown with a [Ga]/([Ga]+[In]) (GGI) gradient across the thickness and a Cu-poor composition. Upon increasing the Cu content towards the CIGS stoichiometry, lower defect density is expected, which should lead to increased absorption in the near-infrared (NIR), diffusion length and carrier collection. Further, optimization of the GGI grading is expected to increase the NIR response. In this contribution [Cu]/([In]+[Ga]) (CGI) values are increased by shortening the deposition stage after the first stoichiometric point. In order to obtain comparable Ga contents at the interface for proper band alignment, the front GGI gradings were actively modified. With a relative CGI increase of 7%, we observe an increased photocurrent, originating from an improved NIR external quantum efficiency response. By characterizing the modified absorber properties by reflection-transmission spectroscopy, we attribute the observed behavior to changes in the optical properties rather than to improved carrier collection. Cu-dependent modifications of the NIR-absorption coefficients are likely to be responsible for the variations in the optical properties, which is supported by device simulations. Adequate re-adjustments of the co-evaporation process and of the alkali-fluorides post-deposition treatments allow maintaining V-oc and FF values, yielding an overall increase of efficien(c)y as compared to a reference baseline. (C) 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.
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