Amorphous AlO₆–SnO₂ nanocomposite electron-selective layers yielding over 21% efficiency in ambient-air-processed MAPbI₃-based planar solar cells

Despite intensive efforts to increase the power conversion efficiency (PCE) of perovskite solar cells (PSCs), the inevitable stress/strain that is occurred in devices and diverse defects generated during the solution process make achieving the theoretical limit of PSCs difficult. Herein, a novel AlO₆–SnO₂ nanocomposite electron-selective layer (ESL) is reported, where amorphous AlO₆ is distributed uniformly in an amorphous SnO₂ network film. Compared with a pristine-SnO₂ ESL, an amorphous AlO₆–SnO₂ ESL increases the size of the perovskite grains achieving a low grain-boundary density, reduces the stress acting as an internal and interfacial nonradiative recombination pathway, exhibits high conductivity and fast charge extraction, and achieves an ideal band offset by upshifting the Fermi level. Through the synergistic multiple-passivation of the AlO₆–SnO₂ ESL, a PCE of 21.04% with a conventional ambient-air-processed methylammonium lead iodide film. In addition, the AlO₆–SnO₂-based PSCs exhibit improved stability and reduced hysteresis, making them promising materials for planar PSC applications.