Stable And Efficient Methylammonium-, Cesium-, And Bromide-Free Perovskite Solar Cells By In-Situ Interlayer Formation

The vast majority of high-performance perovskite solar cells (PSCs) are based on multi-cation mixed-anion compositions incorporating methylammonium (MA) and bromide (Br). Nevertheless, the thermal instability of MA and the tendency of mixed halide compositions to phase segregate limit the long-term stability of PSCs. However, reports of MA-free and/or Br-free compositions are rare in the community since their performance is generally inferior. Here, a strategy is presented to achieve highly efficient and stable PSCs that are altogether cesium (Cs)-free, MA-free and Br-free. An antisolvent quenching process is used to in-situ deposit a polymeric interlayer to promote the growth of phase-pure formamidinium lead tri-iodide perovskite crystals with reduced defect density and to assist in photo-excited charge extraction. The PSCs developed are among the best-performing reported for such compositions. Moreover, the PSCs show superior stability under continuous exposure to both illumination and 85 degrees C heat.