A Smooth CH3NH3PbI3 Film via a New Approach for Forming the PbI2 Nanostructure Together with Strategically High CH3NH3I Concentration for High Efficient Planar‐Heterojunction Solar Cells

The photovoltaic performance of perovskite solar cells (PVSCs) is extremely dependent on the morphology and crystallization of the perovskite film, which is affected by the deposition method. In this work, a new approach is demonstrated for forming the PbI 2 nanostructure and the use of high CH 3 NH 3 I concentration which are adopted to form high‐quality (smooth and PbI 2 residue‐free) perovskite film with better photovoltaic performances. On the one hand, self‐assembled porous PbI 2 is formed by incorporating small amount of rationally chosen additives into the PbI 2 precursor solutions, which significantly facilitate the conversion of perovskite without any PbI 2 residue. On the other hand, by employing a relatively high CH 3 NH 3 I concentration, a firmly crystallized and uniform CH 3 NH 3 PbI 3 film is formed. As a result, a promising power conversion efficiency of 16.21% is achieved in planar‐heterojunction PVSCs. Furthermore, it is experimentally demonstrated that the PbI 2 residue in perovskite film has a negative effect on the long‐term stability of devices.