Two-step fabrication of $$\hbox {MAPbI}₃$$ 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 ((hbox {CH}₃)(hbox { NH}₃)(hbox { PbI}₃) or (hbox {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 ((hbox {PbI}₂)) and second is dip coating (DC) in methylammonium iodide ((hbox {CH}₃hbox {NH}₃hbox {I}) or MAI) solution to prepare a (hbox {MAPbI}₃) perovskite. At the same time, we have also used conventional spin coating (SC) for (hbox {PbI}₂) films and DC in MAI to obtain (hbox {MAPbI}₃) for a comparative study. The gradual formation of (hbox {MAPbI}₃) after dipping a (hbox {PbI}₂) film into MAI solution can be seen from X-ray diffraction patterns. Structural, optical and electrical properties of the (hbox {MAPbI}₃) films are also studied. Better stability of perovskite films was observed using vapour-deposited (hbox {PbI}₂) films as compared with spin-coated (hbox {PbI}₂) films.