Photovoltaic and Amplified Spontaneous Emission Studies of High‐Quality Formamidinium Lead Bromide Perovskite Films

This study demonstrates the formation of extremely smooth and uniform formamidinium lead bromide (CH(NH 2 ) 2 PbBr 3 = FAPbBr 3 ) films using an optimum mixture of dimethyl sulfoxide and N , N ‐dimethylformamide solvents. Surface morphology and phase purity of the FAPbBr 3 films are thoroughly examined by field emission scanning electron microscopy and powder X‐ray diffraction, respectively. To unravel the photophysical properties of these films, systematic investigation based on time‐integrated and time‐dependent photoluminescence studies are carried out which, respectively, bring out relatively lower nonradiative recombination rates and long lasting photogenerated charge carriers in FAPbBr 3 perovskite films. The devices based on FTO/TiO 2 /FAPbBr 3 /spiro‐OMeTAD/Au show highly reproducible open‐circuit voltage ( V oc ) of 1.42 V, a record for FAPbBr 3 ‐based perovskite solar cells. V oc as a function of illumination intensity indicates that the contacts are very selective and higher V oc values are expected to be achieved when the quality of the FAPbBr 3 film is further improved. Overall, the devices based on these films reveal appreciable power conversion efficiency of 7% under standard illumination conditions with negligible hysteresis. Finally, the amplified spontaneous emission (ASE) behavior explored in a cavity‐free configuration for FAPbBr 3 perovskite films shows a sharp ASE threshold at a fluence of 190 μJ cm −2 with high quantum efficiency further confirming the high quality of the films.