Effect of FA+ Fraction and Dipping Time on Performance of FAxMA1−xPbI3 Films and Perovskite Solar Cells
The effects of the formamidinium (FA)+ alloy fraction x and the dipping time on the properties of FAxMA1−xPbI3 thin films (where MA = methylammonium ) as well as the photovoltaic performance of perovskite solar cells (PSCs) have been studied. Mixed-organic-cation FAxMA1−xPbI3 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/FAxMA1−xPbI3/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 fraction x was 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 FAxMA1−xPbI3 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 PbI2 thin films. The PSCs based on FA0.4MA0.6PbI3 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.