Triplet Sensitizer Modification of Poly(3‐hexyl)thiophene (P3HT) for Increased Efficiency in Bulk Heterojunction Photovoltaic Devices

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 ( 1 H NMR and 13 C 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 C 61 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.