A two-terminal perovskite/perovskite tandem solar cell

Building a tandem structure is an effective strategy to enhance the photovoltaic performance of solar cells. In the realization of a two-terminal tandem device, the charge recombination layer (CRL) plays an essential role. In the current study, we demonstrate the first bottom-up solution-processed two-terminal perovskite/perovskite tandem solar cell via developing a novel CRL: spiro-OMeTAD/PEDOT:PSS/PEI/PCBM:PEI. This CRL is efficient to collect electrons and holes at its top and bottom surfaces, and robust enough to protect the bottom perovskite film during the top perovskite film deposition. Moreover, the CRL is prepared by orthogonal solvent processing at low temperature, which is compatible with the pre-deposited perovskite film underneath. The PEI/PCBM:PEI is specially developed for efficient electron collection in both single-junction and tandem perovskite solar cells. With the optimized CRL to bridge the two CH3NH3PbI3 perovskite subcells, the tandem solar cell yields an open-circuit voltage (VOC) of up to 1.89 V that is close to the sum of the two perovskite subcells.