Low-Temperature Nb-Doped SnO₂ Electron-Selective Contact Yields over 20% Efficiency in Planar Perovskite Solar Cells

Low-temperature planar organic–inorganic lead halide perovskite solar cells have been at the center of attraction as power conversion efficiencies go beyond 20%. Here, we investigate Nb doping of SnO 2 deposited by a low-cost, scalable chemical bath deposition (CBD) method. We study the effects of doping on compositional, structural, morphological, and device performance when these layers are employed as electron-selective layers (ESLs) in planar-structured PSCs. We use doping concentrations of 0, 1, 5, and 10 mol % Nb to Sn in solution. The ESLs were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and ultraviolet–visible spectroscopy. ESLs with an optimum 5 mol % Nb doping yielded, on average, an improvement of all the device photovoltaic parameters with a champion power conversion efficiency of 20.5% (20.1% stabilized).