Improving solubility and photovoltaic properties of the star-shaped molecules by synergistic effect of central tris(2-methoxyphenyl)amine and branched fluorine substituent

Abstract Three star-shaped small molecular donors of TOBTC, TOBTC-1F and TOBTC-2F were developed, which adopt tris(2-methoxyphenyl)amine (TPA-OMe) as electron-donating core, as well as nonfluoro-, monofluoro- and difluoro-substituted benzo-thiadiazole as electron-withdrawing branch, respectively. The improved solubility and hole mobility were obtained in comparison to their analogues using TPA as core. More interestingly, the TOBTC-2F:PC71BM blend exhibited highest hole mobility (μh) of 8.5 × 10−4 cm2V−1s−1 and its solution-processed organic solar cell displayed the best photovoltaic properties with a power conversion efficiency of 4.5% at an area of 10 mm2 without any additive and annealing treatment. Here, the μh value is 10 times higher than that of its TPA based analogue:PC71BM blend. It indicates that the synergistic effect of the TPA-OMe unit in core and fluorine substituents in benzo-thiadiazole is available to improve solubility, mobility and photovoltaic properties of the star-shaped small molecular donors.