Reduced Interface-Mediated Recombination for High Open-Circuit Voltages in CH₃ NH₃ PbI₃ Solar Cells

Perovskite solar cells with all-organic transport layers exhibit efficiencies rivaling their counterparts that employ inorganic transport layers, while avoiding high-temperature processing. Herein, it is investigated how the choice of the fullerene derivative employed in the electron-transporting layer of inverted perovskite cells affects the open-circuit voltage (V_OC ). It is shown that nonradiative recombination mediated by the electron-transporting layer is the limiting factor for the V_OC in the cells. By inserting an ultrathin layer of an insulating polymer between the active CH₃ NH₃ PbI₃ perovskite and the fullerene, an external radiative efficiency of up to 0.3%, a V_OC as high as 1.16 V, and a power conversion efficiency of 19.4% are realized. The results show that the reduction of nonradiative recombination due to charge-blocking at the perovskite/organic interface is more important than proper level alignment in the search for ideal selective contacts toward high V_OC and efficiency.