Novel Low-Temperature Process for Perovskite Solar Cells with a Mesoporous TiO2 Scaffold

The most efficient organic inorganic perovskite solar cells (PSCs) contain the conventional n-i-p mesoscopic device architecture using a semiconducting TiO2 scaffold combined with a compact TiO2 blocking layer for selective electron transport. These devices achieve high power conversion efficiencies (15-22%) but mainly require high temperature sintering (>450 degrees C), which is not possible for temperature-sensitive substrates. Thus far, comparably little effort has been spent on alternative low-temperature (<150 degrees C) routes to realize high-efficiency TiO2-based PSCs; instead, other device architectures have been promoted for low temperature processing. In this paper the compatibility of the conventional mesoscopic TiO2 device architecture with low temperature processing is presented for the first time with the combination of electron beam evaporation for the compact TiO2 and UV treatment for the mesoporous TiO2 layer. Vacuum evaporation is introduced as an excellent deposition technique of uniform compact TiO2 layers, adapting smoothly to the rough fluorine-doped tin oxide substrate surface. Effective removal of organic binders by UV light is shown for the mesoporous scaffold. Entirely low-temperature-processed PSCs with TiO2 scaffold reach encouraging stabilized efficiencies of up to 18.2%. This process fulfills all requirements for monolithic tandem devices with high-efficiency silicon heterojunction solar cells as the bottom cell.