Planar Type Trivalent Bismuth Based Pb-Free Perovskite Solar Cells

An 8% stable planar type trivalent Bi-based Cs3Bi2I9 perovskite-sensitized solar cell (P-SSC) was demonstrated by fabricating a glass/FTO (F doped tin oxide)/TiO2/Cs3Bi2I9/PTAA (poly-triary-lamine)/Au construction. The Cs3Bi2I9 perovskite film formed by Cs3Bi2I9/N,N-dimethylformamide/HI solution featured a pure crystalline phase and excellent thermal stability. The unencapsulated Cs3Bi2I9 P-SSC maintained its initial efficiency for >500 h under continuous light soaking by 1 Sun at 65 degrees C and 60-70% relative humidity. Its functional stability may be due to the trivalent Bi based perovskite structure being more robust than the divalent Pb based perovskite one.