Two-step fabrication of MAPbI3 perovskite thin films with improved stability

Perovskite solar cells (PSCs) are a part of an emerging technology in photovoltaics (PV), which uses perovskite-structured hybrid compounds as light absorbers such as methylammonium lead iodide (CH3NH3PbI3 or MAPbI(3)). PSCs with a record certified efficiency of 22.1% are among the fastest advancing PV technology; but PSCs suffer from fast degradation in the presence of moisture. PSCs prepared by a solution process have additional limitation of small device area. In order to improve the stability of perovskite layer, we have used a two-step method for depositing a perovskite layer. First step is the thermal evaporation of lead iodide (PbI2) and second is dip coating (DC) in methylammonium iodide (CH3NH3I or MAI) solution to prepare a MAPbI(3) perovskite. At the same time, we have also used conventional spin coating (SC) for PbI2 films and DC in MAI to obtain MAPbI(3) for a comparative study. The gradual formation of MAPbI(3) after dipping a PbI2 film into MAI solution can be seen from X-ray diffraction patterns. Structural, optical and electrical properties of the MAPbI(3) films are also studied. Better stability of perovskite films was observed using vapour-deposited PbI2 films as compared with spin-coated PbI2 films.