Zr Incorporation into TiO<sub>2</sub> Electrodes Reduces Hysteresis and Improves Performance in Hybrid Perovskite Solar Cells while Increasing Carrier Lifetimes

We investigate zirconium (Zr) incorporation into the titanium dioxide (TiO<sub>2</sub>) electron-transporting layer used in organometal halide perovskite photovoltaics. Compared to Zr-free controls, solar cells employing electrodes containing Zr exhibit increased power conversion efficiency (PCE) and decreased hysteresis. We use transient photovoltage and photocurrent extraction to measure carrier lifetimes and densities and observe longer carrier lifetimes and higher charge densities in devices on Zr-containing electrodes at microsecond times as well as longer persistent photovoltages extending from ∼milliseconds to tens of seconds. We characterize the surface stoichiometry and change in work function and reduction potential of the TiO<sub>2</sub> upon incorporation of Zr and discuss the charge recombination at the TiO<sub>2</sub> interface in the context of these variables. Finally, we show that the combination of Zr–TiO<sub>2</sub> electrode modification with device pyridine treatment leads to a cumulative improvement in performance.