Above 600 mV Open-Circuit Voltage BiI3 Solar Cells

Tiwari, Devendra, Alibhai, Dominic and Fermin, David J (2018) Above 600 mV Open-Circuit Voltage BiI3 Solar Cells. ACS Energy Letters, 3 (8). pp. 1882-1886. ISSN 2380-8195

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Abstract

Phase-pure BiI3 films obtained by versatile gas-phase iodination of Bi2S3 are investigated as an absorber in photovoltaic devices. This preparation method leads to highly crystalline BiI3 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 SnO2 (FTO) substrate, exhibiting an indirect band gap transition at 1.72 eV. High-level calculations based on G0W0 approximation are used to rationalize the electronic structure of BiI3, confirming the band gap value estimated experimentally. The films show p-type conductivity with an acceptor density on the order of 1015 cm–3. Solar cells with the architecture glass/FTO/TiO2/BiI3/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.

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