PHPIT, a new kind of intramolecular donor-acceptor side-chain-tethered hexyl-phenanthrenyl-imidazole polythiophene, is synthesized. The more balanced electron and hole mobilities and the enhanced visible- and internal-light absorptions in the devices consisting of annealed PHPIT/PCBM blends both contribute to a much higher short-circuit current density, which in turn led to a power conversion efficiency as high as 4.1%.