Study of perovskite solar cells based on mixed-organic-cation FA x MA 1−x PbI 3 absorption layer

Mixed-organic-cation FAxMA1-xPbI3 films were prepared using a one-step solution deposition method in ambient air. The formamidinium (FA+) fraction 'x' was varied from 0.1 to 1 by changing the amounts of formamidinium iodide (FAI) and methylammonium iodide (MAI) in the precursor solution. Perovskite solar cells (PSCs) with a structure of FTO glass/compact TiO2/mesoporous TiO2/FAxMA1-xPbI3/carbon electrode were designed and fabricated. The effects of the FA+ fraction 'x' on the structure, morphology and optical properties of the FAxMA1-xPbI3 films as well as the photovoltaic performance of PSCs were studied. The results showed that the photovoltaic inactive δ-phase FAPbI3 can be formed in the presence of high contents of FA+ (x = 0.8 and 1.0). The band gap of FAxMA1-xPbI3 decreased from 1.58 eV to 1.49 eV when the FA+ fraction x increased from 0.1 to 1. The PSCs based on FA0.4MA0.6PbI3 exhibited an optimal photovoltaic performance, yielding Voc of 0.8 V, Jsc of 22.84 mA cm-2, FF of 0.48 and PCE of 8.77%.