Mixed-Organic-Cation (FA)x(MA)1-xPbI3 Planar Perovskite Solar Cells with 16.48% Efficiency via a Low-Pressure Vapor-Assisted Solution Process

Compared to that of methylammonium lead iodide perovskite (MAPbI(3)), formamidinium lead iodide perovskite (FAPbI(3)) has a smaller energy band gap and greater potential efficiency. To prevent the transformation of a-FAPbI(3) to 6-FAPbI(3), preparation of (FA)(x)(MA)(1-x)PhI3 was regarded as an effective route. Usually, the planar (FA)(x)(MA)(1-x)PbI3 perovskite solar cells are fabricated by a solution process. Herein, we report a low-pressure vapor assisted solution process (LP-VASP) for the growth of (FA)(x)(MA)(1-x)PbI3 perovskite solar cells that features improved electron transportation, uniform morphology, high power conversion efficiency (PCE), and better ciystal stability. In LP-VASP, the (FA)(x)(MA)(1-x)PbI3 films were formed by the reaction between the PbI2 film with FAI and MAI vapor in a Very simple vacuum oven. LP-VASP is an inexpensive 14y to batch-process solar cells, avoiding the repeated deposition solution process for PbI2 films, and the device had a low cost: We demonstrate that, with an increase in the MAI content, the (101) pOk position of FAPbI(3) shifts toward the (110) peak position of MAPbI(3), the (FA)(x)(MA)(1-x)PbI3 perovskites are stable, and no decomposition or phase transition is observed after 14 days. The photovoltaic performance was effectively improved by the introduction of MA+ with the highest efficiency being 16.48% under conditions of 40 wt % MAI. The carrier lifetime of (FA)(x)(MA)(1-x)PbI3 perovskite films is approximately three times longer than that of pure FAPbI(3). Using this process, solar cells with a large area of 1.00 cm(2) were fabricated with the PCE of 8.0%.