TiO2 and SnO2 thin films will be synthesized in various structural forms, applicable as electron selective interfaces of the negative electrode of perovskite solar cell (PSC). Reference materials will be TiO2 (anatase, rutile) single crystals. The properties of thin films, single crystals and interfaces will be investigated by standard spectroscopic, analytical and microscopic techniques with the focus at electrochemical impedance, voltammetry and photoelectron spectroscopy (in ultrahigh vacuum and in nearly-ambient pressures). The aim is to address the films' quality and to elucidate the conduction band energetics in variety of interfaces (solid-vacuum , -gas, -liquid, -solid) from model ones to those used in practical PSCs. The goal is to explain the existing discrepancies about conduction band-alignment in various oxide semiconductors, including face-specific effects in TiO2. The second goal is to demonstrate the optimum interfaces for electron-selective terminal of PSC, both by model experiments and by construction of full PSC devices.