Controllable Crystallization of CH₃NH₃Sn_0.25Pb_0.75I₃ Perovskites for Hysteresis‐Free Solar Cells with Efficiency Reaching 15.2%

Abstract

While SnPb alloyed perovskites have been considered as an effective approach to broaden the absorption spectrum, it is still challenging to modify the crystallization (and thus morphology, crystallinity, and orientation) in a controllable manner and thus boost the efficiency of SnPb alloyed perovskite solar cells. Here, it is unveiled that controlling the crystallization of CH 3 NH 3 Sn 0.25 Pb 0.75 I 3 films can be simply realized by adjusting the amount of dimethyl sulfoxide in precursors, which has not been reported in SnPb alloyed perovskite systems. The remarkable perovskite crystallinity enhancement by the 20‐fold enhanced (110) plane intensity in the X‐ray diffraction spectrum of CH 3 NH 3 Sn 0.25 Pb 0.75 I 3 and the preferred (110) orientation with the texture coefficient enhanced by 2.6 times to reach 0.88 are demonstrated. Importantly, it is discovered that the introduction of dimethyl sulfoxide avoids the formation of the colloidal coagulation observed in prolonged‐storage precursors and ameliorates inhomogeneous Sn/Pb distributions in resultant perovskite films. Through optimizing perovskite films and device structures, hysteresis‐free planar‐heterojunction CH 3 NH 3 Sn 0.25 Pb 0.75 I 3 solar cells with the efficiency reaching 15.2%, which are the most efficient SnPb alloy‐based perovskite solar cells, are achieved.