Above 600 mV Open-Circuit Voltage BiI₃ Solar Cells

High Resolution Image Download MS PowerPoint Slide Phase-pure BiI 3 films obtained by versatile gas-phase iodination of Bi 2 S 3 are investigated as an absorber in photovoltaic devices. This preparation method leads to highly crystalline BiI 3 films featuring a rhombohedral phase and a high-degree of stacking order. The films are composed of micrometer-sized flat grains distributed homogeneously across the F-doped SnO 2 (FTO) substrate, exhibiting an indirect band gap transition at 1.72 eV. High-level calculations based on G 0 W 0 approximation are used to rationalize the electronic structure of BiI 3, confirming the band gap value estimated experimentally. The films show p-type conductivity with an acceptor density on the order of 10 15 cm –3 . Solar cells with the architecture glass/FTO/TiO 2 /BiI 3 /F8/Au, where F8 is poly(9,9-di- n -octylfluorenyl-2,7-diyl), display a record open-circuit voltage above 600 mV and overall power conversion efficiency of 1.2% under AM 1.5G illumination. The large open-circuit potential is rationalized in terms of carrier lifetimes longer than 1 ns as probed by time-resolved photoluminescence spectroscopy.