Air-stable bismuth sulfobromide (BiSBr) visible-light absorbers : optoelectronic properties and potential for energy harvesting

Guo, Xiaoyu and Huang, Yi-Teng and Lohan, Hugh and Ye, Junzhi and Lin, Yuanbao and Lim, Juhwan and Gauriot, Nicolas and Zelewski, Szymon J. and Darvill, Daniel and Zhu, Huimin and Rao, Akshay and McCulloch, Iain and Hoye, Robert L. Z. (2023) Air-stable bismuth sulfobromide (BiSBr) visible-light absorbers : optoelectronic properties and potential for energy harvesting. Journal of Materials Chemistry A, 11 (42). pp. 22775-22785. ISSN 2050-7488 (https://doi.org/10.1039/D3TA04491B)

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Abstract

ns2 compounds have recently attracted considerable interest due to their potential to replicate the defect tolerance of lead-halide perovskites and overcome their toxicity and stability limitations. However, only a handful of compounds beyond the perovskite family have been explored thus far. Herein, we investigate bismuth sulfobromide (BiSBr), which is a quasi-one-dimensional semiconductor, but very little is known about its optoelectronic properties or how it can be processed as thin films. We develop a solution processing route to achieve phase-pure, stoichiometric BiSBr films (ca. 240 nm thick), which we show to be stable in ambient air for over two weeks without encapsulation. The bandgap (1.91 ± 0.06 eV) is ideal for harvesting visible light from common indoor light sources, and we calculate the optical limit in efficiency (i.e., spectroscopic limited maximum efficiency, SLME) to be 43.6% under 1000 lux white light emitting diode illumination. The photoluminescence lifetime is also found to exceed the 1 ns threshold for photovoltaic absorber materials worth further development. Through X-ray photoemission spectroscopy and Kelvin probe measurements, we find the BiSBr films grown to be n-type, with an electron affinity of 4.1 ± 0.1 eV and ionization potential of 6.0 ± 0.1 eV, which are compatible with a wide range of established charge transport layer materials. This work shows BiSBr to hold promise for indoor photovoltaics, as well as other visible-light harvesting applications, such as photoelectrochemical cells, or top-cells for tandem photovoltaics.

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