Large-area, high-quality organic-inorganic hybrid perovskite thin films via a controlled vapor-solid reaction

A new vapor-solid reaction (VSR) method is demonstrated, in which two parallel hot plates were used to synthesize high-quality organic-inorganic hybrid perovskite thin films over an area of 8 x 8 cm(2). We first probed the VSR process in detail, and found side reactions between methylammonium iodide (MAI) vapor and lead iodide (PbI2) occurring, which could be largely suppressed by inserting a PEDOT:PSS layer beneath. Furthermore, we employed an in situ resistance measurement method to monitor the evolution of perovskite thin films, which provided valuable insights for precise control of film growth. Inverted planar perovskite solar cells with a decent efficiency of 12.2% have been achieved. Our work provides not only a strategy to fabricate high-quality perovskite thin films over a large area, but also a reliable way to optimize the reaction parameters of perovskite. In addition, our finding reveals that both the precise control of the ratio of MAI to PbI2 and the proper choice of substrates are decisive for achieving high-performance devices during the VSR process.