Nontoxic and Less Toxic Hybrid Perovskites: a Synergistic Strategy for Sustainable Photovoltaic Devices

A research hotspot for the last decade, organometal‐halide perovskites are now showing their promise in numerous optoelectronic devices. With power conversion efficiency (PCE) greater than 25%, perovskite solar cells (PSCs) are approaching the status of popular monocrystalline silicon–based solar cells (SCs). However, the presence of a bioaccumulative lead (Pb) in these perovskite compounds hinders their scalability and commercialization. The endeavor on nontoxic alternatives has triggered a new field of perovskites where Pb has been successfully eliminated. Preliminary studies of photovoltaic (PV) devices based on Pb‐free perovskites have shown some promise; however, they failed to exhibit comparable performance and compositional stability. Therefore, to exploit together the advantages of high efficiency and lesser toxicity, combinations of Pb alternatives with each other as well as with conventional Pb are required in the perovskite framework to fabricate hybrid perovskites (HPVKs). The first part of this Review briefly discusses all possible Pb substitutes and their limitations in PV devices. Based on the Pb contents, the second part elaborates on the two different types of HPVKs (i.e., nontoxic and less toxic) and their progress in photovoltaics. The Review concludes with an outlook discussing current challenges in the way of HPVKs and prospective opportunities to assess their future progress.