Due to the high power conversion efficiency, easy preparation process and lowcost, organometal halide perovskite solar cells have developed into one of the most promising photovoltaic devices. It has been found that it is effective to reduce the defect state located in perovskite film via interfacial modification of the perovskite layer. In this paper, ACN additive with low concentration was introduced into Spiro-OMeTAD precursor to modify the perovskite interfaces. ACN additive can dissolve impurities in the surface of the perovskite layer, leading to the formation of an inter-diffusion structure between perovskite and Spiro-OMeTAD layers. Consequently, the method can improve the electrical contact of hole transport layer and decrease recombination losses originated from dislocation defect or dangling bond. Consequently, the corresponding best performance device generates conversion efficiency of 17.9%, 11.4% higher than that of the pristine device.
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