Reduced Interface-Mediated Recombination for High Open-Circuit Voltages in CH3NH3PbI3 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 CH₃NH₃PbI₃ 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.

Perovskite solar cells have emerged as one of the most promising solar-cell technologies for the next generation of photovoltaics. Despite simple and cheap processing, the solar cells exhibit comparably little loss in open-circuit voltage. An approach to further reduce this loss by optimizing the charge selectivity of the fullerene-based electron contact in efficient devices is shown.

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