Perovskite solar cells: Beyond methylammonium lead iodide

Organic-inorganic lead halide based perovskites solar cells are by far the highest efficiency solution-processed solar cells, threatening to challenge thin film and polycrystalline silicon ones. Despite the intense research in this area, concerns surrounding the long-term stability as well as the toxicity of lead in the archetypal perovskite, CH₃NH₃PbI₃, have the potential to derail commercialization. Although the search for Pb-free perovskites have naturally shifted to other transition metal cations and formulations that replace the organic moiety, efficiencies with these substitutions are still substantially lower than those of the Pb-perovskite. The perovskite family offers rich multitudes of crystal structures and substituents with the potential to uncover new and exciting photophysical phenomena that hold the promise of higher solar cell efficiencies. In addressing materials beyond CH₃NH₃PbI₃, this Perspective will discuss a broad palette of elemental substitutions, solid solutions, and multidimensional families that will provide the next fillip toward market viability of the perovskite solar cells.