Cu_1–xCs_xInSe₂: Candidate Absorber for Higher Conversion Efficiency and Broader Band Photodetector

Abstract

Exploring the improvement of power conversion efficiency (PCE) and potential in the photodetection of devices fabricated by copper based thin film materials is very meaningful. For this, we systematically study the crystal and electronic structures of CuInSe 2 (CISe) doped by the Cs element and investigate the device performance with Cs-doped CISe as an absorber. The result shows that the substitution of Cs for Cu can significantly change the crystal structure, which leads to the decrease of the band gap from 1.04 to 0.767 eV and the variation of the electronic states at the Fermi level. One doping case with the band gap of 1.009 eV is considered a promising candidate for the absorber and exhibits a PCE up to 23.37% higher than 19.2% of CISe, which demonstrates the excellent performance of narrow band gap photovoltaic cells. We find that by adjusting the content of Cs, the detectivity of Cs:CISe devices can reach 2.36 × 10 14 Jones at 1200 nm and the detection wavelength can be extended to 1620 nm while maintaining the detectivity at a 10 12 Jones level. The results suggest that doping Cs into the CISe absorber layer can further improve the conversion efficiency of copper based thin film solar cells and exhibits promising photodetection performance.