Efficient Wide-Bandgap Mixed-Cation and Mixed-Halide Perovskite Solar Cells by Vacuum Deposition

Vacuum deposition methods are increasingly applied to the preparation of perovskite films and devices, in view of the possibility to prepare multilayer structures at low temperatures. Vacuum-deposited, wide-bandgap solar cells based on mixed cation and mixed anion perovskites have been scarcely reported, due to the challenges associated with the multiple-sources processing of perovskite thin-films. In this work, we describe a 4-sources vacuum deposition process to prepare wide-bandgap perovskites of the type FA1-nCsnPb(I1-xBrx)3 with tunable bandgap and controlled morphology, using FAI, CsI, PbI2 and PbBr2 as the precursors. The simultaneous sublimation of PbI2 and PbBr2 allows to decouple and control the relative Br/Cs content, resulting in homogeneous perovskite films with bandgap in the 1.7 eV-1.8 eV range and no detectable halide segregation. Solar cells based on 1.75 eV bandgap perovskites show efficiency up to 16.8% and promising stability, maintaining 90% of the initial efficiency after 2 weeks of operation.