Vacuum thermal-evaporated SnO₂ as uniform electron transport layer and novel management of perovskite intermediates for efficient and stable planar perovskite solar cells

Tin oxide (SnO₂) has been confirmed as a vital electron transport material for efficient planar perovskite solar cells (PSCs) owing to its outstanding electrical and optical properties. Defectively, the SnO₂ electron transport layer (ETL) by spin coating still remains great challenges for repeatable planar heterojunction PSCs fabrication for its limited scale and incompetent uniformity. Herein, the vacuum thermal-evaporation procedure is employed to achieve this intent by the dense and uniform SnO₂ layer, which can largely improve the material utilization for cost reduction and act as a potential for the prospective industrial large-scale fabrication. Besides, a post-annealing treatment of evaporated SnO₂ is proved obbligato to achieve an ideal crystallinity improvement. Furthermore, to remove the antisolvent method for perovskite, methyl ammonium acetate (MAAc) worked as an additive into the perovskite precursor for a pure MAPbI₃ film to achieve the poisonous antisolvent free. Noticeable, the formation of an unstable MAPbI_3-xAc_x intermediate certainly has a great impact on the resulting perovskite, in which the particular surface-morphology was dominated by the MAAc volatilization rate. The obtained morphology with fluctuant pits and ridges, like a 3D-structure, contributes to more light absorption and contact area at perovskite/charge transport material interface, leading to higher photocurrent, more efficient charge extraction and better device performance. As a result, an optimal cell device can remain 86% of its initial photovoltaic performance (PCE: 16.79%) after a 50-d storage in air.