The differences in crystal structure and phase of lead-free perovskite solar cell materials

Hybrid organic-inorganic lead halide perovskite materials have established themselves as a competitive solar cell technology, with high efficiencies and simple processing. However the main drawback of these materials is currently their stability, which is complicated by the potential to release the toxic element lead into the environment. Attempts to replace lead for less-toxic starting materials have generated significant research interest. Any candidate material must have enhanced stability and comparable performance to lead halide perovskites, and an understanding of the structure is key to developing these materials to be competitive. This review provides a brief overview and reference of experimentally determined crystal structures of lead-free perovskite materials. The most promising potential materials are identified as those that maintain a cubic structure, particularly double-perovskite type absorbers.