Exploring the deposition pathway in the notch region of double-graded bandgap ACIGS solar cells

Abstract

The bandgap widening of Ag-alloyed Cu(In,Ga)Se2 (ACIGS) thin films poses a significant challenge in enhancing their photocurrent. This study demonstrates correlations between element diffusion behavior and notch-point formation in ACIGS films, which ultimately influence the resulting current circuit voltage and fill factor. Our findings delineate a novel approach for fabricating a suitably tailored band gap grading in ACIGS, which serves as a bottom subcell in tandem configuration. This was achieved by modulating a wide range of process temperatures from 340 to 470 °C, which were measured by pyrothermal, to assess the GGI profile during deposition. Experiments were undertaken to variate the second-stage conditions, striving to sustain the photocurrent, mitigate defects, and enhance crystallinity, achieving an impressive performance of 17.7 % without applying post-deposition treatments or anti-reflection coatings. The efficiencies surpassing 8 % were achieved as we measured these cells under a 715 nm long-pass filter, which corresponds to the bandgap of a typical top cell in tandem applications (1.73 eV photon energy). These results emphasize the significance of understanding the deposition temperature and its impact on the properties of ACIGS films, paving the way for further advancements in solar-cell technology.