Enhanced Photovoltaic Performance of the Inverted Planar Perovskite Solar Cells by Using Mixed-Phase Crystalline Perovskite Film with Trace Amounts of PbI2 as an Absorption Layer

It is widely known that solvent engineering has a significant effect on the growth of high quality perovskite film. However, the crystal evolution process and crystal compositions of perovskite film when applying the two-step method are multifaceted, and the effects on the photoelectrical properties for the perovskite layer still require further study. In this study, the above two issues are systematically studied. Combining the XRD and photoluminescence spectra results, it was observed that the residual PbI 2 decreased with the increase of DMSO in DMSO/DMF solvents and that there were two types of local phase crystallites (disordered and ordered) in the perovskite films. The phase transitions of the crystals were investigated with the ratio of DMSO increasing in the mixed solvents. In addition, the interfacial defect states in the PbI 2 /perovskite interface which can act as charge carrier trapping centers were significantly affected by the photo(dark) conductivity of the perovskite film. It was also observed that the photoconductivity of the perovskite film with the DMSO 30%, which contains mixed-phase (ordered/disordered) crystals and trace amounts of PbI 2, was higher than the film with DMSO 60%. Finally, a high power conversion efficiency of 16.5% with trace amounts of PbI 2 was achieved when the volume ratio of the DMSO was 30%.