We present the successful synthesis of a modified poly(3-hexyl)thiophene (P3HT) donor polymer with benzophenone (P3HTB) substitution. The triplet-sensitizer (benzophenone)-containing polymer (P3HTB) was synthesized by the oxidative copolymerization of 3-hexylthiophene and benzopheneone-modified thiophene [2-phenyl-2-(4-(thiophen-3-yl)phenyl)-1,3-dioxolane] and deprotecting the cyclic ketal group. The resulting polymer was characterized by using nuclear magnetic resonance spectroscopy (1H NMR and 13C NMR) and Fourier transform infrared spectroscopy (FTIR). Different ratios of the copolymer (P3HTB) and pristine P3HT mixtures were used for the fabrication and characterization of bulk heterojunction (BHJ) cells, with [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) used as the acceptor in fabricating the active layers. An increase in power conversion efficiency (≈15 %) was observed with devices fabricated with 2.5 and 5 wt % P3HTB mixed with P3HT compared to those fabricated with P3HT alone.