Interfacing Low‐Temperature Atomic Layer Deposited TiO2 Electron Transport Layers with Metal Electrodes

Low‐temperature atomic layer deposited (ALD) TiO2 is an electron transport layer that is relatively unreactive with mixed halide perovskite semiconductors. This amorphous, ALD‐grown metal oxide is typically interposed between the perovskite layer and a low work function metal electrode, prompting interest in the electronic and chemical structure of the resulting TiO2/metal interface. Here, the interfaces between TiO2 and two common metal low work function electrodes, polycrystalline thin films of silver and aluminum are studied. It is found that a Schottky barrier forms between Ag and low‐temperature ALD‐grown TiO2, consistent with the observed solar cell current–voltage characteristics, and confirmed by in situ measurement of Ag deposition‐induced core level shifts in X‐ray photoelectron spectra and barrier height extraction from temperature‐dependent current–voltage data. On the other hand, Al reacts chemically with the surface of TiO2 during its deposition. The resulting interface acts as an Ohmic contact, due to the apparent oxygen vacancy doping of the underlying ALD‐TiO2. These findings provide lessons for metal electrode selection in future halide perovskite device structures.