Factors influencing the performance of paintable carbon-based perovskite solar cells fabricated in ambient air

To date, many efforts have been made to improve the performance of paintable carbon-based （PC-based） perovskite solar cells （PSCs）. Though great progress has been achieved, their power conversion efficiencies are still relatively low compared with hole-transport-materials-based PSCs. General research on influencing factors of performance in PC-based PSCs is still insufficient. In this work, PC-based PSCs were fabricated in ambient air and four groups of controlled experi- ments were performed in which the PbI2 layers were prepared with or without antisolvent extraction treatment. These four groups of experiments were designed to find out the effect of different influencing factors on PC-based PSCs performance, for example, PbI2 residual, the surface morphology of the perovskite film, the surface roughness of the perovskite film, and the contact status of the perovskite/carbon electrode interface. With a systematic analysis, we demonstrated that the contact status of the perovskite/carbon electrode interface played a vital role in PC-based PSCs, and a fiat, smooth perovskite surface could help to improve this contact status significantly. Besides, on the precondition of a poor contact interface, no PbI2 residual and a good surface morphology only brought limited benefits to the performances of PC-based PSCs.