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 °C), which is not possible for temperature-sensitive substrates. Thus far, comparably little effort has been spent on alternative low-temperature (<150 °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.