Effect of substituents on the aggregate structure and photovoltaic property of violanthrone derivatives

Abstract In this paper, three violanthrone derivatives with different substituents, 16,17-bis(2-ethylhexyloxy)-anthra[9,1,2- cde -]benzo[ rst ]pentaphene-5,10-dione ( 3 ), 16,17-bis(octyloxy)-anthra[9,1,2- cde -]benzo[ rst ]pentaphene-5,10-dione ( 4 ), 16,17-bis(hexyloxy)-anthra[9,1,2- cde -]benzo[ rst ]pentaphene-5,10-dione ( 5 ), are synthesized. It is found that the substituent has a great effect on the aggregate structures of violanthrone derivatives: the shorter the side chain is, the stronger the intermolecular π–π actions in the solid state is. Because all compounds are p-type semiconductive materials with the relatively low-lying highest occupied molecular orbital (HOMO) energy levels (∼−5.1 eV) and low band gaps (∼1.8 eV), their photovoltaic properties are evaluated when the blends of violanthrone derivatives and [6,6] -phenyl-C 61 -butyric acid methyl ester (PCBM) (1:1, w/w) are used as the active layers of organic solar cells. Among three violanthrone derivatives, compound 5 exhibits the best photovoltaic performance with the power conversion efficiency (PCE) of 0.54% since the aggregate structure of compound 5 is in favor of charge transport.