Reducing regioisomers of fullerene-bisadducts by tether-directed remote functionalization: investigation of electronically and sterically isomeric effects on bulk-heterojunction solar cells.

C60 bis-adduct containing a mixture of regio-isomers with different LUMO energy levels and steric geometries could greatly affect the morphological and bulk properties. To investigate the regio-isomer effect on solar cell performance, we have successfully designed and synthesized a regio-selective 4-acetatephenyl-4′-methylphenylmethano C60 bis-adduct (S-APM-CBA) by “tether-directed remote functionalization” strategy and a random 4-acetatephenyl-4′-methylphenylmethano C60 bis-adduct denoted as R-APM-CBA by traditional cyclopropanation. The dramatic reduction in the number of regio-isomers in S-APM-CBA is confirmed by the 1H NMR and HPLC measurements and theoretical calculation. Compared to the R-APM-CBA-based device with a Jsc of 6.63 mA/cm2, an FF of 44.3% and a PCE of 2.46%, the device using S-APM-CBA yielded a much lower Jsc of 1.48 mA/cm2, an FF of 32.2%, and a PCE of 0.38%. Consistently, the electron-only device using S-AMP-CBA exhibited lower electron mobility than the R-AMP-CBA-based device. These r...