Gallium (Ga)-doped zinc-oxide (ZnO) nanoparticles (NPs) were synthesized by using a polymer pyrolysis method. The smallest size of the obtained 4-mol% Ga-doped zinc-oxide (GZO) spherical NPs was approximately 10-15 nm, and the presence of Ga was confirmed by using X-ray photoelectron spectroscopy. To examine the role of GZO NPs, fabricated hybrid polymer solar cells (HPSCs) by using blends of a conjugated polymer poly (3-hexalthiophene) as an electron donor and crystalline GZO NPs as an electron acceptor. Significant improvements in the short-circuit current density and fill factor compared to these for the undoped ZnO (UZO) NPs were achieved by using the GZO NPs. This suggests that the GZO NPs have higher electron mobility than the UZO NPs and possess great potential for use as electron acceptor in HPSCs.