Two-step fabrication of MAPbI_3 perovskite thin films with improved stability

摘要

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 (CH3NH3PbI_3 or MAPW3). 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 (PbI_2) 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 PbI_2 films and DC in MAI to obtain MAPbI_3 for a comparative study. The gradual formation of MAPbI_3 after dipping a PbI_2 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 PbI_2 films as compared with spin-coated PbI_2 films.