Quantum dots show great promise for fabrication of hybrid bulk heterojunction solar cells with enhanced power conversion efficiency, yet controlling the morphology and interface structure on the nanometer length scale is challenging. Here, we demonstrate quantum dot-based hybrid solar cells with improved electronic interaction between donor and acceptor components, resulting in significant improvement in short-circuit current and open-circuit voltage. CdS quantum dots were bound onto crystalline P3HT nanowires through solvent-assisted grafting and ligand exchange, leading to controlled organic-inorganic phase separation and an improved maximum power conversion efficiency of 4.1% under AM 1.5 solar illumination. Our approach can be applied to a wide range of quantum dots and polymer hybrids and is compatible with solution processing, thereby offering a general scheme for improving the efficiency of nanocrystal hybrid solar cells.