Using interface engineering to tune excitonic properties of halide and mix-halide hybrid perovskite thin films

ZnO electron transport layers of various morphologies are implemented to modify the exciton binding energy and charge extraction from hybrid perovskite (PVSK) thin films. The ZnO susbtrates employed include single crystalline (SC), micro-structured (MS), and nano-structured (NS) ZnO. Characterization of the PVSK-ZnO interface is achieved via electron microscopy, which is correlated to interfacial charge transfer via temperature, power, and time-resolved photoluminescence (PL) spectroscopy. SC-ZnO is observed to act as an effective electron extraction layer as indicated by PL intensity quenching, reduced recombination lifetime and reduced exciton density in the PVSK thin film. On the other hand, MS- and NS-ZnO result in PL enhancement, while reducing recombination lifetime. These trends change with temperature and can be associated with variations in exciton binding energy of PVSK, underlining the effect of the electron extraction layer on the excitonic properties of the PVSK film. We conclude that while SC-ZnO can be used for electron extraction in photovoltaic devices, MS- and NS-ZnO can be implemented as scaffold in optical devices that require high quantum yield.