Ultrafast Low-Temperature Crystallization of Solar Cell Graded Formamidinium-Cesium Mixed-Cation Lead Mixed-Halide Perovskites Using a Reproducible Microwave-Based Process

National Funds through FCT, Foundation for Science and Technology, under the projects ALTALUZ (PTDC/CTM-ENE/5125/2014) and SUPER SOLAR (PTDC/NAN-OPT/28430/2017). M.J.M. also acknowledges funding by FCT through the Grant SFRH/BPD/115566/2016.The control of morphology and crystallinity of solution-processed perovskite thin-films for solar cells is the key for further enhancement of the devices' power conversion efficiency and stability. Improving crystallinity and increasing grain size of perovskite films is a proven way to boost the devices' performance and operational robustness, nevertheless this has only been achieved with high-temperature processes. Here, we present an unprecedented low-temperature (