Three solution-processable triphenylamine (TPA)-containing low band gap D-A-D molecules with benzothiadiazole (BT) as acceptor unit and TPA-(4-hexyl)thiophene (TPA-HT), TPA-(4-hexyl)thieno[3,2-b]thiophene (TPA-HTT) and bis(octyloxy)TPA-(4-hexyl)thieno[3,2-b]thiophene (boTPA-HTT) as donor units, TPA-HT-BT, TPA-HTT-BT and boTPA-HTT-BT, have been designed and synthesized for the application in the bulk-heterojunction organic solar cells (OSCs). The molecules show broad absorption band in the visible range and appropriate HOMO energy levels for the donor materials in OSCs. The OSC devices were fabricated with the molecules as donor and PC70BM as acceptor. The power conversion efficiencies of the OSCs based on TPA-HT-BT, TPA-HTT-BT and boTPA-HTT-BT reached 1.44%, 1.44% and 0.75%, respectively, under the illumination of AM.1.5, 100 mW/cm2.Graphical abstractResearch highlights► TPA-containing D-A-D molecules with benzothiadiazole (BT) as acceptor unit show good solubility and broad absorption. ► PCE of the OSCs based on the molecule as donor and PC70BM as acceptor reached 1.44%. ► Thieno[3,2-b]thiophene-vinylene pi-bridge in the molecules broadened the absorption spectra.