Reducing interface recombination boosts the Voc for perovskite solar cells.

Even though perovskite solar cells have reached 22% efficiency within a very short span, the presence of lead is a major bottleneck to its commercial application. Tin and Germanium based perovskites failed to be viable replacements due to the instability of their +2 oxidation states. Antimony could be a possible replacement, forming perovskites with structure A3M2X9. However, solution processing of Cs, organic ammonium based Sb perovskites result in the formation of the dimer phase with poor charge transport properties. Here we demonstrate that Rb can template the formation of the desired layered phase irrespective of processing methodologies, enabling the demonstration of efficient lead-free perovskite solar cells.