Enhanced Efficiency and Stability of an Aqueous Lead-Nitrate-Based Organometallic Perovskite Solar Cell

We investigate the stability of an active organometallic perovskite layer prepared from a two-step solution procedure, including spin coating of aqueous lead nitrate (Pb(NO₃)₂) as a Pb²⁺ source and sequential dipping into a methylammonium iodide (CH₃NH₃I) solution. The conversion of CH₃NH₃PbI₃ from a uniform Pb(NO₃)₂ layer generates PbI₂-free and large-grain perovskite crystallites owing to an intermediate ion-exchange reaction step, resulting in improved humidity resistance and, thereby, improved long-term stability with 93% of the initial power conversion efficiency (PCE) after a period of 20 days. The conventional fast-converted PbI₂-dimethylformamide solution system leaves small amounts of intrinsic PbI₂ residue on the resulting perovskite and MAPbI₃ crystallites with uncontrollable sizes. This accelerates the generation of PbI₂ and the decomposition of the perovskite layer, resulting in poor stability with less than 60% of the initial PCE after a period of 20 days.