Influence of metal substitution on hybrid halide perovskites: towards lead-free perovskite solar cells

The revolutionary impact of hybrid halide perovskites in the field of solution-based photovoltaics has made them one of the most-promising technologies for next-generation solar cells. However, such a breakthrough has natural drawbacks, since all these perovskite materials yielding high efficiency contain lead as a primary element in their chemical composition. There is hence a substantial hurdle for their acceptance in industries and society alike. Substitution of lead in the perovskite structure by a suitable nontoxic metal has therefore become one of the significant pivotal challenges associated with these wonder materials of the present decade. We hereby review the progress in this emerging field of research to summarize the influence of alternative elements in replacing lead vis-a-vis the materials' properties and characteristics of solar cells based on the metal-substituted hybrid halide perovskites. Moreover, we have discussed the prospects of next-generation of lead-free perovskites, namely 2D layered perovskites, defect ordered and double perovskites with a focus on their properties, stability, and photovoltaic applications.