Abstract: A dye unit, 3-ethyl rhodanine, was attached onto (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) for the first time, affording a new fullerene acceptor PCBM-rhodanine (PCBRh) for polymer solar cells (PSCs) with enhanced light absorption. The successful attachment of the rhodanine moiety was confirmed by H NMR, 3C NMR and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopies. UV-vis spectroscopic study indicated that PCBRh had stronger absorptions in the region of 300~600 nm than PCBM, and this was due to the high absorption coefficient of the dye unit of 3-ethyl rhodanine. Cyclic voltammetric measurement revealed that the lowest unoccupied molecular orbital (LUMO) level of PCBRh was 0.1 eV higher than that of PCBM, which can be understood by considering the electron donating property of the rhodanine moiety. Using PCBRh as an acceptor blending with poly(3-hexylthiophene-2,5-diyl) (P3HT), the bulk heterojunction (BHJ) PSC device exhibited a power conversion efficiency (PCE) of 146% under the optimized condition (blending ratio of P3HT:PCBM=1:1 (mass ratio), annealing treatment at 135 ℃ for 10 min). The effect of annealing on the morphology of P3HT:PCBRh active layer and its correlation with the device performance were studied by atomic force microscopy (AFM), revealing that in the annealed P3HT:PCBRh blend film P3HT aggregated to long stripes with an average length of ca. 20 nm and the RMS roughness increased compared to that for the reference P3HT:PCBM blend film, thus leading to unfavorable exciton diffusion and dissociation.

Key words: polymer solar cell, fullerene, functionalization, 3-ethyl rhodanine, (6,6)-phenyl-C61 butyric acid methyl ester (PCBM)