Increased open-circuit voltage in bulk-heterojunction solar cells using a C60 derivative

The fullerene derivative C60-fused N-methyl-2-(3-hexylthiophen-2-yl)pyrrolidine (C60-TH-Hx) is used as the acceptor material in bulk-heterojunction (BHJ) solar cells fabricated with the low band-gap polymer poly[(4,4′-bis(2-ethylhexyl)dithiene[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-5,5′-diyl]. Direct comparison with BHJ solar cells based on [6,6]-phenyl-C61-butyric methyl ester and Si-PCPDTBT indicates that the C60-TH-Hx acceptor yields a larger open-circuit voltage because of higher lowest unoccupied molecular orbital energy level of C60-TH-Hx.