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- C ₆₁ -butyric methyl ester and Si-PCPDTBT indicates that the C ₆₀ -TH-Hx acceptor yields a larger open-circuit voltage because of higher lowest unoccupied molecular orbital energy level of C₆₀ -TH-Hx.