Co-axial electrospray: a versatile tool to fabricate hybrid electron transporting materials for high efficiency and stable perovskite photovoltaics

We report a cost-effective and simple co-axial electrospray technique to fabricate a hybrid electron transporting material (ETM) consisting of a nanocomposite of hierarchically structured TiO₂ nanobeads (NBs) blended with ZnO nanofibers (NFs), namely ZnO NFs + TiO₂ NBs, for the first time ever. Owing to its large surface area, highly porous nature and fast electron transport, the hybrid ETM is further used in methylammonium lead iodide (CH₃NH₃PbI₃)-based perovskite solar cells (PSCs). The optimized cells utilizing the hybrid ETM exhibit a maximum power conversion efficiency (PCE_max) of 20.27%, the highest efficiency reported thus far for hybrid ETMs. Moreover, negligible hysteresis and highly reproducible values of PCE are observed for such cells. The PCE of devices based on the ZnO NF + TiO₂ NB hybrid ETM is found to be far superior to that of only ZnO NF and hierarchically structured TiO₂ NB-based ETMs. Light-induced transient measurement shows that the significantly rapid electron diffusion and longer electron lifetime of the ZnO NF + TiO₂ NB hybrid ETM than of only ZnO NF and hierarchically structured TiO₂ NB-based ETMs contribute to the enhanced efficiency in PSCs.