Effect of FA+Fraction and Dipping Time on Performance of FAxMA1-xPbI3Films and Perovskite Solar Cells

The effects of the formamidinium (FA)(+)alloy fractionxand the dipping time on the properties of FA(x)MA(1-x)PbI(3)thin films (where MA = methylammonium ) as well as the photovoltaic performance of perovskite solar cells (PSCs) have been studied. Mixed-organic-cation FA(x)MA(1-x)PbI(3)thin films were prepared using a two-step solution deposition method in ambient air. PSCs with fluorine-doped tin oxide glass/compact TiO2/mesoporous TiO2/FA(x)MA(1-x)PbI(3)/carbon electrode structure were fabricated, aiming to reduce the fabrication costs and improve the stability of PSCs. The results indicated that, when the FA(+)alloy fractionxwas increased from 0 to 1, the x-ray diffraction (XRD) peaks shifted continuously to lower angle, while the absorption edge and photoluminescence (PL) peak shifted continuously towards longer wavelength. The Raman spectra of the FA(x)MA(1-x)PbI(3)thin films, consisting of five typical peaks at 68.5 cm(-1), 77.5 cm(-1), 84.6 cm(-1), 139.1 cm(-1), and 283.2 cm(-1), barely shifted with incorporation of FA(+). In addition, the dipping time was shortened by using mixed solvents to prepare the PbI(2)thin films. The PSCs based on FA(0.4)MA(0.6)PbI(3)prepared with a dipping time of 15 min exhibited the highest average power conversion efficiency (PCE) of 8.64%, with 74.4% of the initial efficiency being retained after exposure to ambient air at room temperature with approximately 50% humidity for 700 h.