Defect passivation is an efficient strategy for improving the performance of perovskite solar cells (PSCs). In this study, we introduced a benzodithiophene-based 2D spacer with a short alkyl chain (BDT-C2) into a perovskite film for defect passivation. The introduction of BDT-C2 did not exhibit the 2D perovskite structure, but an optimized amount (0.01 wt%) induced vertically oriented (110) planes of perovskite film. However, when excess BDT-C2 was added to the perovskite film, the orientation collapsed. The nanostructure of the film was correlated with the device performance. The (110) plane was mostly arranged in the vertical orientation, and the device performance was best under the optimal conditions. Despite the enhancement of the device performance, the grain size of the perovskite was almost unaltered with the addition of BDT-C2. By measuring the light intensity-dependent V-oc and J(sc), we confirmed that there was reduced charge recombination owing to defect passivation under the optimal conditions.

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