Abstract
While interfacial and grain-boundary passivation presently attract enormous research interest for perovskite solar cells (PSCs), the improvement of Cs-(FAPbI(3))(X)(MAPbBr(3))(Y) bulk quality still lacks systematical study, especially for constructing polycrystalline layers in planar configurations. Here, a DMSO-molecule-process for improving the quality of Cs-(FAPbI(3))(0.85)(MAPbBr(3))(0.15) is developed, where the molar ratio of precursors, the kind of anti-solvents, and speed-time profiles are found critical. The optimized treatment significantly enhanced the crystal orientation, grain size, surface roughness, photo-response, carrier lifetime, and contact potential difference of absorbers. Cs-(FAPbI(3))(0.85)(MAPbBr(3))(0.15) absorbers also present superior charge transport, as well as reduced carrier recombination and decreased trap densities via DMSO-molecule-control, enabling performance improvement on both long-term stability and photovoltaic parameters of 1cm(2) PSCs. Champion planar cells demonstrated a power conversion efficiency (PCE) of 21.07% (0.159cm(2)) and PCE of 19.4% (1cm(2)) with negligible hysteresis. Moreover, 1cm(2) devices retained 90% of initial PCE after aging 50 days in ambient air.