Tuning composition space in lead-free divalent and tetravalent halide perovskite : a critical review

In this review, we have portrayed a comparative analysis between the recent progress of divalent and tetravalent lead-free hybrid perovskites, which have been in the focus of sustainable and green environment as clean energy materials for the last several years. The plethora of such hybrid perovskite materials have been emerged as the promising candidate not only from the review of photovoltaic applications, but also for other optoelectronic devices. This has been manifested in the form of several theoretical and experimental investigations for a wide range of hybrid perovskite family members, where a perfect amalgamation of profound theoretical understanding with the possible implications of such materials for the energy scavenging is yet to be achieved completely. Several issues including efficiency, stability, and toxicity are required to be addressed from a holistic approach. This paves the way to the foundation of this review, where we have not only shed light on the fundamental understanding of these materials, but also to their possible implications. The presence of lead in the hybrid perovskite material is certainly a matter of concern from the toxicity viewpoint, despite the enhanced efficiency of the photovoltaic devices based on such materials. Therefore, an ongoing quest has been observed in last few years to replace lead, while at the same time, not compromising the efficiency and stability of the devices. This review is focused on these investigations that we have witnessed in lead free divalent and tetravalent hybrid perovskite materials from a critical comparative insight with a future roadmap of these exciting materials family to be envisaged in the coming years.