We developed a perovskite formulation and deposition by spin-coating for flat substrates which led to a substantial increase in efficiency. We also developed sequential evaporation techniques involving thermal evaporation of the metallic compounds followed by infiltration of the organo-halide compounds in solution. This proved to be compatible with textured substrates including thermal evaporation, atomic layer deposition and magnetron sputtering. Silicon heterojunction cells were developed and optimised for the use in tandems with both flat or textured front. A recombination of layers to flat and textured interfaces was designed to pair the sub cells together. The top transparent contact was improved to be compatible with the temperature sensitive perovskite, while retaining good electrical and optical properties.

At the time of publication, these PK/Si tandem cells held the world record efficiency of 25.2%. The high efficiencies demonstrated, as well as the advantages of proximity to the high penetration of Si technology in photovoltaic markets makes this approach interesting for established Si cell manufactures looking to boost their cell efficiency at reduced additional costs.