Three small molecules named DR3TBDTT, DR3TBDTT-HD and DR3TBD2T with benzo[1,2-b:4,5-b']dithiophene (BDT) unit as the central building block have been designed and synthesized for solution processed bulk-heterojunction solar cells. PCEs of 8.12% (certified 7.61%) and 8.02% under AM 1.5G irradiation (100 mWcm(-2)) have been achieved for DR3TBDTT and DR3TBDTT based photovoltaic devices with PC71BM as acceptor, respectively. The better PCEs are achieved by improving the Jsc without scarifying the high Voc and FF through the strategy of taking both the advantages of conventional small molecules and polymers for OPV.