Efficient bandgap widening in co-evaporated MAPbI(3) perovskite

Co-evaporated perovskite solar cells (PSCs) have demonstrated outstanding properties, such as great scalability, intrinsic stability, high-power conversion efficiency (PCE), and fabrication adaptability even on rough surfaces. At present, MAPbI3 is the most used co-evaporated perovskite due to the complexity of forming multi-component compositions by thermal evaporation. Even though PSCs with high PCEs have been obtained, the MAPbI3 bandgap (∼1.60 eV) is not ideal for multijunction devices. In this work, we propose a facile method to increase the bandgap of co-evaporated MAPbI3 (∼1.60 eV) through a MABr-based treatment. The best MABr-treated perovskite composition films show a bandgap of 1.66 eV (MAPb(Br0.18I0.82)3) and exhibit good spectral stability under continuous 1-sun illumination at the ambient conditions of 28 °C and 70% relative humidity. This hybrid method works efficiently for thick co-evaporated MAPbI3 films (∼750 nm), which is unusual for hybrid processes. The n-i-p PSCs built from the MAPb(Br0.18I0.82)3 films exhibit a blue-shifted external quantum efficiency and a Voc increase of ∼30 mV as compared to the pure MAPbI3 PSCs, in agreement with the bandgap widening observed in the films. This hybrid method to crete wide bandgap perovskites can be universally applied to MAPbI3 deposited on both flat and textured surfaces and shows great promise for its integration in monolithic tandems.