While individual perovskite and organic solar cells have demonstrated remarkable performance, achieving similar success in high-efficiency perovskite/organic tandem solar cells (TSCs) has been challenging, primarily due to large voltage deficits and severe non-radiative recombination. By exploring the fundamental mechanisms of carrier losses, we identify that imbalanced carrier transport, particularly inadequate hole transport in the organic subcell significantly limits the overall performance of perovskite/organic TSCs. Herein, we implement a hole transport self-assembled monolayer (SAM) anchored to MoO