An Ab Initio Study of Clusters as Building Blocks for Crystals: From Prussian Blue Analogs to Hybrid Perovskites

Cluster‐based crystals containing the (Nb 6 Cl 12 ) 2+ or (Ta 6 Cl 12 ) 2+ clusters, including the well‐known Nb 6 Cl 14 , K 4 Nb 6 Cl 18 , and the Prussian blue analog (Me 4 N) 2 [MnNb 6 Cl 12 (CN) 6 ], have been investigated by density functional theory. The electronic structure of the cluster is the same for all compounds, with a semiconducting gap of around 1 eV between occupied and empty states, in the range of interest for solar energy applications. Calculations suggest that these clusters could be used as cations in hybrid organic–inorganic perovskites, as a substitute for toxic Pb 2+ . Moreover, bandgaps, band alignment, and hydrogen adsorption calculations show that the designed cluster‐based hybrid perovskites have potential as intermediate band materials for photovoltaics, and as photocatalysts for the hydrogen evolution reaction.