LAUSR

Abstract Methylammonium lead triiodide (MAPbI3) has been investigated as the recent most exciting light absorber materials for photovoltaics. Printable perovskite solar cells based on MAPbI3 in a TiO2/ZrO2/Carbon triple-layer mesoporous scaffold have shown simple fabrication process and impressive stability. Moving towards formamidinium lead triiodide (FAPbI3) as the light absorber, which has a bandgap of 1.48 eV that matches the optimum bandgap (1.34 eV) of a single-junction solar cell, will result in further improvement in power conversion efficiency. However, it is challenging to deposit high-quality FAPbI3 in a 10-μm-thick mesoporous scaffold due to the incomplete one-step conversion of perovskite precursors restrained in the mesoporous scaffold. Here we report printable perovskite solar cells with high-quality Cs0.1FA0.9PbI3 absorber inside mesoporous scaffolds using a mixed solvent vapor assisted crystallization approach. A power conversion efficiency of 15% is obtained with a spectral response up to 840 nm. The phase transition and crystal growth of Cs0.1FAPbI3 are carefully monitored in the mesoporous scaffold. This work not only opens up new methods for fabricating efficient and stable solar cells but also provides a deeper understanding of crystal growth inside constrained nanostructures.