Highly efficient and stable inverted planar solar cells from (FAI)x(MABr)1-xPbI2 perovskites

We report highly efficient and stable inverted planar lead mixed-halide (Br, I) perovskite solar cells with a configuration of ITO/poly(3-bromothiophene)/(FA)(y)(MA)(1-y)PbBrxI3-x/C-60/BCP/Ag (FA: HC(NH2)(2)(+); MA: CH3NH3+). We found that small changes in the composition of (FA)(y)(MA)(1-y)PbBrxI3-x have big impact on the material properties and device performance. Appropriate Br-doping enlarges MAPbBr(x)I(3-x)'s bandgaps and prolongs the life of the excited charge carrier, which leads to higher device open-circuit voltage (V-OC). Replacing MA with FA extends the absorption of (FA)(y)(MA)(1-y)PbBrxI3-x which compensates the J(SC) loss in MAPbBr(x)I(3-x) from Br-doping. The optimized perovskite film with a composite of FA(0.8)MA(0.2)PbBr(0.2)I(2.8) shows a lifetime of 670 ns and a photoelectric response to 830 nm, resulting in an enhanced J(SC) of 22.2 mA cm(-2), a high FF of 0.80, and an efficiency of 18.1%. In addition, the inverted device based on FA(0.8)MA(0.2)PbBr(0.2)I(2.8) showed long-term stability with 80% efficiency remained after 4 months in a glovebox without encapsulation. Our results demonstrate highly efficient and stable inverted planar perovskite solar cells can be achieved by optimizing absorber material composition, which offer a reference for their applications in flexible or tandem solar cells.