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Effects of defect states on the performance of CuInGaSe2 solar cells

Device modeling has been carried out to investigate the effects of defect states on the performance of ideal CuInGaSe2 (CIGS) thin film solar cells theoretically. The varieties of defect states (location in the band gap and densities) in absorption layer CIGS and in buffer layer CdS were examined. The performance parameters: open-circuit voltage, short-circuit current, fill factor, and photoelectric conversion efficiency for different defect states were quantitatively analyzed. We found that defect states always harm the performance of CIGS solar cells, but when defect state density is less than 1014 cm−3 in CIGS or less than 1018 cm−3 in CdS, defect states have little effect on the performances. When defect states are located in the middle of the band gap, they are more harmful. The effects of temperature and thickness are also considered. We found that CIGS solar cells have optimal performance at about 170 K and 2 μm of CIGS is enough for solar light absorption.