Lead-Free Perovskite Derivatives Toward Eco-Friendly Indoor Photovoltaics

Indoor photovoltaics present a compelling solution for powering the ever-expanding array of Internet-of-Things (IoT) smart sensors in a sustainable manner. The emergence of halide perovskites as promising absorbers for indoor photovoltaics has ignited significant interest due to their favorable optoelectronic characteristics. Nevertheless, the deployment of indoor photovoltaic devices in close proximity to end-users raises concerns about the toxicity associated with the lead content found in mainstream halide perovskites. This has spurred the search for alternative, lead-free perovskite derivatives for efficient indoor photovoltaics without lead toxicity concerns. We first demonstrated this concept with Cs₃Sb₂I_9-<i>x</i>Cl<i>_x</i>, enabling indoor photovoltaic efficiencies already in the range of mainstream, commercial indoor photovoltaics. Furthermore, our investigations revealed that the spectroscopic limited maximum efficiency for this and other lead-free perovskite derivatives under indoor lighting conditions can reach approximately 60%, showcasing their immense potential through further materials and device optimization. In fact, the demonstrated photovoltaic efficiency of Cs₃Sb₂I_9-<i>x</i>Cl<i>_x</i> was sufficient to power printed digital gates via millimeter-scale indoor photovoltaic devices, confirming the opportunity already provided by this technology toward self-powered electronics with potentially low environmental impact. We extended our exploration to Cu-Ag-Bi-I absorbers, tailoring the microstructure and device architecture to achieve enhanced indoor photovoltaic efficiencies and ensuring reliable operation under realistic illuminance levels as low as 200 lux, all while exhibiting favourable air stability. Recognizing the importance of sustainability in emerging technologies, we additionally conducted a thorough assessment of the environmental impacts of various lead-free perovskite derivatives in the context of indoor photovoltaics. Our findings identified the most promising compositions from a sustainability perspective, offering crucial guidance to the research community developing lead-free perovskite derivatives to enable eco-friendly self-powered smart sensors for a green IoT revolution.