The influence of polymer/fullerene morphology on photodetector performance is reported. Various morphologies of spin-coated films are generated by different blending ratio. Morphological study combined with measurement of charge carrier mobility reveals that blend films with an excess content of crystalline fullerene have a phase-separated morphology, resulting in enhanced charge carrier mobility. Under this phase separated morphology, photovoltaic performance is enhanced because of the generation of percolating pathways for charge carriers. Interestingly, however, a homogeneous morphology is found to be more beneficial for photodetector application than this phase separated morphology. An optimized device displayed 3 dB bandwidth up to 1 kHz and detectivities up to D = 1.1 × 10(10) cm Hz(1/2) W(-1). These results emphasize the importance of developing an independent strategy for designing high performance photodetectors separately from solar cell devices both in terms of materials and device geometry. Possible relations between morphology and various figures of merit of photodetectors are discussed.