New C84 derivative and its application in a bulk heterojunction solar cell

We report here the synthesis and characteristics of a new C-84 adduct ([84]PCBM), realized via a diazoalkane addition reaction. [84] PCBM was obtained as a mixture containing three major isomers. [84]PCBM was tested in a fullerene/poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-p-phenylene vinylene) (MDMO-PPV) bulk heterojunction solar cell as the first C84 derivative to be applied in device fabrication. Spin coating the active layer blend from 1-chloronaphthalene ( the very best fullerene solvent) instead of ortho-dichlorobenzene was necessary to obtain the more efficient photovoltaic device. The PV results indicate that the hole mobility of MDMO-PPV may not be increased upon blending with [84] PCBM. This explains the relatively low I-SC of the device as due to the buildup of space charge. The V-OC of the device is similar to 500 mV lower than that of the one with [60] PCBM, while [ 84] PCBM has a 350 mV higher electron affinity than [60] PCBM. This loss surpasses the linear relation between the donor(HOMO)-acceptor(LUMO) energy gap and the VOC in this type of device. A maximum power conversion efficiency of 0.25% was reached for the MDMO-PPV:[84] PCBM cells.