Thermal stability of mobility in methylammonium lead iodide

Metal halide perovskites (MHPs) are a fascinating class of photovoltaic materials; possessing distinctive optoelectronic properties and simple processing routes. The most significant remaining barrier to commercialization is their poor stability under ambient conditions. While the stability of electronic parameters in this class of material has been studied extensively, to date the overwhelming majority of such studies have been carried out using PV devices. The presence of electrodes and transport layers in this approach involves both implicit encapsulation, and modification of interface properties. To develop an extensive understanding of environmental stability of electronic properties in MHPs, it is crucial to study the electronic properties of the material in isolation, rather than in a finished device. In this work, we have studied the thermal stability of electronic properties of solution processed methylammonium lead iodide (MAPbI(3)). MAPbI(3) thin films were subjected to extended periods of elevated temperatures before their electronic properties were probed using time-resolved microwave conductivity (TRMC), a contactless technique enabling extraction of a proxy for the material's mobility, without the need to form a device. The films were analysed with x-ray absorption spectroscopy (XAS) to study the impact of temperature on film microstructure. We observed an increase in average Pb-I bond length with increased annealing temperature.