In this work, the perovskite solar cells(PSCs) were fabricated with the bandgap-tunable(FA)_x(MA)_(1-x)PbI_3 absorber layers through a facile two-stage deposition route.The doping was realized by adding the formamidinium iodide(FAI) into a precursor MAI solution.Both the surface morphology and electrochemical impedance spectra(EIS) were conducted to evaluate the absorber layers or solar cells.After the optimization, the best PSC performance of 14.73% was achieved at a nominal FAI content of 12.5 at.%.The performance enhancement was attributed to both the enhancement of visible light harvesting and carrier transport capability.Besides, the stability of a PSC device based on the single MAPbI_3 absorber layer was also investigated, and a power conversion efficiency(PCE) of 11.27 % remained even after laying in vacuum for 10 days.
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