RESUMO
A light harvest layer composed of gradual change from formamidinium lead triiodide (FAPbI3) to methylammonium lead triiodide (MAPbI3) was fabricated using a novel two-step process. That is, a graded halide layer structure without extra processing steps is demonstrated. Conventionally, in the fabrication of MAPbI3 perovskite solar cells (PSCs) using two-step process, PbI2 layer was the first deposited on a mesoporous TiO2 coated substrate. The methylammonium iodide (MAI) solvent was then spin-coated on the surface of PbI2 layer and heated to form the MAPbI3 perovskite layer. Double perovskite layers such as FAPbI3 plus MAPbI3 requires twice of the second step which FAI and MAI should be spin-coated individually. This can be tedious and time consuming. We report here a facile way to form a graded perovskite layer, consisting FAPbI3 to MAPbI3, in a single step. FAI was first added into dimethylformamide (DMF) solution that was used to form PbI2 layer, then MAI solution was dripped on top of the FAI/PbI2 layer. The graded perovskite layer structure (FAPbI3/MAPbI3) in a gradient manner are readily formed, where the structure is confirmed by EDS to be FTO/compact TiO2/mesoporous TiO2/FAPbI3(thin)/MAPbI3/Spiro-OMeTAD/Ag. The Jsc, and Voc of solar cells with this graded perovskite layer are enhanced and the efficiency increases from 11.62% to 14.06%.
