2D Ruddlesden–Popper perovskites are promising candidates for energy-harvesting applications because of their tunable optical properties and ambient stability. Moreover, they are solution-processable and compatible with scalable manufacturing via various printing techniques. However, such methods often induce large degrees of heterogeneity because of poorly controlled crystallization. We address this issue by blending the well-known 2D perovskite (PEA)2PbBr4 with an organic small molecule, C8-BTBT. Terahertz (THz) absorption and temperature-dependent photoluminescence (PL) spectroscopy studies revealed changes in the photophysical properties of the perovskite without affecting its structural integrity upon adding C8-BTBT. The inclusion of trace amounts of C8-BTBT results in defect passivation both at perovskite platelet boundaries and at surfaces, as indicated by increased carrier lifetimes and substantially increased photoluminescence quantum yields (PLQY). This improves the responsivity of photodetectors using the 2D perovskite as an active layer. Our study highlights a straightforward strategy for fabricating high-quality 2D perovskites via large-area processing techniques.