High efficiency planar Sn-Pb binary perovskite solar cells: controlled growth of large grains via a one-step solution fabrication process

One-step solution fabrication of high-performance Sn-including perovskite solar cells (PSCs) is very challenging due to the rapid crystallization of the Sn-based perovskite layer, leading to a poor film morphology and low surface coverage. In this work, a well-controlled one-step method, assisted by a multi-step solvent treatment, is developed for the growth of a high-quality CH₃NH₃Pb_(1−x)Sn_xI₃ (0 ≤ x ≤ 1) perovskite film on a planar PEDOT:PSS substrate. The CH₃NH₃Sn_0.25Pb_0.75I₃ perovskite films consisting of densely packed and uniformly distributed large crystal grains were obtained using sec-butyl alcohol solvent engineering and N,N-dimethylformamide solvent annealing under an N₂ atmosphere. The CH₃NH₃Sn_0.25Pb_0.75I₃-based PSCs with a maximum power conversion efficiency (PCE) of 12.08% and an average PCE of 11.01% were obtained. The PSCs also exhibit excellent performance reproducibility, good air stability and weak hysteresis behavior. The enhancement in the performance of the PSCs is attributed to the well-crystallized CH₃NH₃Sn_0.25Pb_0.75I₃ film, resulting in simultaneous improvement in charge-carrier transport properties and reduction in charge-carrier recombination, a very promising approach to obtain high performance Sn-including perovskite solar cells.