Optimizing quality of lead-free perovskite thin film with anti-solvent engineering and co-doping SnBr2/SnF2; its solar cell performance

Lead-free perovskite film is crucial for non-toxicity device applications and tin-based perovskite is one of most promising non-toxic perovskites. In this study, Br and F doping and anti-solvent washing process were investigated for suitable MASnI3 perovskite film. The structural, morphological and optical analyses showed the only Br or F doping is not enough to obtain of tin-based perovskite films having high crystallinity, surface coverage and absorbance properties. The Br and F co-doping (1 M(MAI):0.6 M(SnI2):0.2 M(SnBr2):0.2 M(SnF2)) has caused significantly decrease in morphological defects and increase crystallinity. Moreover, addition to the co-doping, void-free film morphology has been obtained by anti-solvent washing process: toluene:chloroform (1:1 vol%). Thus, oxidation of Sn2+ to Sn4+ was successfully suppressed. The optimized Sn-based perovskite film has band gap energy of 1.31 eV and atomic ratio determined to be 1.00:0.15:0.03 from the EDS and 1.00:0.16:0.07 from the XPS for I:Br:F, which indicates I-rich stoichiometric content. The solar cell application has been also performed in device structure of ITO/PEDOT:PSS (60 nm)/perovskite (272 nm)/PCBM (70 nm)/Al (100 nm). The best solar cells prepared using the co-doped perovskite films without and with anti-solvent washing process have PCE values of 2.25% with Jsc 14.9 mA/cm(2), Voc 0.42 V and FF 36% and 4.45% with Jsc 17.8 mA/cm(2), Voc 0.48 V and FF 52%, respectively.