The project aims to systematically investigate wide band gap (1.7 eV) perovskite solar cells prepared via the thermal evaporation method from the perspectives of defect formation mechanism and crystallisation kinetics. We will target wide bandgap CsPbI3 single-junction perovskite solar cells with a PCE of over 20%, which will pave the way for development of high performance and large area perovskite-silicon tandem solar cells.