A set of hybrid rod–coil diblock copolymers containing different sizes of poly(3-hexylthiophene-2,5-diyl) (P3HT) as the rod block and a polystyryl-type (PS) coil block with covalently linked polyoxometalates (POMs) as side chains have been synthesized. The P3HT rod blocks, synthesized using Grignard metathesis polymerization, and the PS coil block, prepared by atom transfer radical polymerization were successfully coupled using “click” chemistry to form the rod–coil diblock copolymers (PS-PTn). POM cluster attachment was performed on the diblock copolymers through a post-polymerization functionalization approach. The thin film morphology of the diblock copolymers prior to cluster attachment shows a strong dependence on the solvent and the size of the P3HT block. Following cluster attachment, the hybrid diblock copolymers show much less solvent and size dependence in phase-separated morphologies of their pristine films. The sporadic and isolated conducting domains seen in the pristine films change to widespread worm-like conducting networks after thermal annealing; such morphologies are conducive to photovoltaic properties.