Investigation on the role of amines in the liquefaction and recrystallization process of MAPbI3 perovskite†
The amine-induced very fast liquefaction and recrystallization (L&R) process on organic–inorganic hybrid perovskites has been demonstrated to be an effective way to improve the quality of the as-deposited MAPbI3 films and increase the feasibility of preparing large area perovskite solar cells (PSCs). Despite the effectiveness, the reaction mechanism of the L&R process is yet to be well understood. In this work, we investigate the fundamental influences of amines on the structural change of MAPbI3 perovskite by studying the reaction between ammonia and a bulk MAPbI3 crystal. By employing various techniques including in situ X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy, we find that NH3 effectively substitutes iodine in the perovskite crystal lattice, transforming the 3-dimensional (3D) lattice into a MAPb(NH3)nI3 coordination complex-based system. The resulting coordination complex octahedral structures are only held together by weak forces of attraction, leading to the experimentally observed L&R process. First-principles calculations further confirm the feasibility of such L&R at room temperature. As a proof of concept, we demonstrated the use of liquefaction for substrate recycling of MAPbI3 based solar cells with ammonia. Our results here provide deep insights for understanding the interaction mechanism, which can surely provide important guidance on improving the quality of perovskite films and related devices, as well as the recycling of toxic lead for long-term sustainability.