Alkyl substituted [6,6]-thienyl-C61-butyric acid methyl esters: easily accessible acceptor materials for bulk-heterojunction polymer solar cells

Abstract

[6,6]-Thienyl-C₆₁-butyric acid ester derivatives with methyl, hexyl and 2-ethylhexyl at the 5-position of thiophene ring (TCBM-Cn, n represents the number of carbon atom in the alkyl chain) were synthesized. Unlike [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM), these methanofullerene derivatives ([6,6] adduct) can be directly obtained from the typical diazo addition under mild conditions, and high temperature isomerization is unnecessary. With a hexyl or 2-ethylhexyl group at the 5-position of thiophene, the solubility of TCBM-Cn in chlorobenzene is as high as 180 ± 10 mg ml⁻¹. Bulk heterojunction photovoltaic solar cells were fabricated with a device structure of ITO/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/poly(3-hexylthiophene) (P3HT) : TCBM-Cn (1 : 0.8 w/w)/LiF/Al. The device based-on TCBM-C6 exhibited the best performance with a power conversion efficiency (PCE) of up to 4.26%.