A critical review on bismuth and antimony halide based perovskites and their derivatives for photovoltaic applications: recent advances and challenges

In the past decade, lead halide perovskites experienced impressive progress in photovoltaics with the certified device conversion efficiency over 25%, owing to their outstanding optoelectronic properties. However, the toxicity and environmental instability of the core lead halide materials would strongly limit their commercialization. Within this scenario, research investigations directed at assessing the properties and opportunities offered by emerging lead-free halide perovskites are becoming everyday more relevant to pinpoint new low-cost/low-toxicity solutions for solar-to-electricity conversion. In this review, group VA metal halide based perovskites, namely those of bismuth (Bi) and antimony (Sb), and their derivatives with different valence states are classified based on the formulae A(3)B(2)X(9)and A(2)AgBX(6), also known as double perovskites, and AgaBibXa+3b, called rudorffites (A = MA, FA, Cs, Rb,etc.; B = Bi, Sb; X = I, Br, Cl). Here, we summarize the recent progress in the exploitation of these materials, with special attention devoted to the description of the crystal structures, thin film preparation methods and performances in real devices, including both theoretical insights and experimental observations. With this survey, we are able to provide reasonable perspectives for the future development of high-performance photovoltaic devices based on lead-free bismuth/antimony halide based perovskites and their derivatives.