Carbazole-containing fullerene derivatives for P3HT-based bulk-heterojunction solar cells

Two carbazole-substituted fullerene derivatives, N-methyl-[9-(2-ethylhexyl)-9H-carbazole-2-yl]-pyrrolidine (CBZPYR-C60) and [9-(2-ethylhexyl)-9H-carbazole-2-yl] C61-butyric acid methyl ester (CBZBME-C60), were synthesized through a 1,3-dipolar cycloaddition of an azomethine intermediate and a tosylhydrazone route, respectively. The synthesized CBZPYR-C60 and CBZBME-C60 showed good solubility in common organic solvents such as chloroform, toluene, and 1,2-dichlorobenzene. The synthesized fullerene derivatives were characterized by 1H and 13C NMR, FAB-MS, FT-IR, UV–visible absorption, and fluorescence spectroscopy. The electrochemical properties of the fullerenes and morphologies of the P3HT:acceptor layers were also investigated through cyclic voltammetry (CV) and atomic force microscopy (AFM), respectively. P3HT-based bulk-heterojunction photovoltaic devices were fabricated by using CBZPYR-C60 and CBZBME-C60 as the electron acceptors. The photovoltaic devices were fabricated with a layered structure of ITO/PEDOT:PSS/P3HT:acceptor/LiF/Al. Composite ratios of P3HT to the fullerene derivatives of 1:0.5, 1:0.7, and 1:1 were used in the active layers. The device performance of these organic solar cells was determined by the open-circuit voltage (Voc), short-circuit current density (Jsc), and fill factor (FF). The highest power conversion efficiencies (PCEs) of the devices fabricated using CBZPYR-C60 and CBZBME-C60 were 1.90% and 2.29%, respectively, with a composite ratio of 1:0.7.