Transient Energy-Resolved Photoluminescence Study of Excitons and Free Carriers on FAPbBr3 and FAPbBr3/SnO2 Interfaces

Abstract

Lead bromide perovskites have a larger band gap and are significantly more stable than their iodine counterparts, offering the perspective for higher voltage, tandem photovoltaics exceeding the Shockley-Queisser limit, and shorter time to deployment of photovoltaics. However, their efficiencies still need to be rivaling the iodine ones. Herein, the photophysics of FAPbBr3 and the ones behind electron transfer from FAPbBr3 to SnO2, one of the most effective electron transporting materials (ETMs), are reported. Time- and energy-resolved photoluminescence studies revealed the existence of two emitting states in the perovskite, which were assigned to bounded excitons and free carriers. SnO2 extracted electrons from excitons and free carriers, with a selectivity related to the SnO2 surface treatment. This new insight helps explain SnO2’s unique qualities as an ETM to produce photovoltaics with reduced voltage losses. Furthermore, this study illustrates the importance of performing time- and energy-resolved photoluminescence to capture the intricacies of the photophysical process.