•A small molecule DCAEH5TBT with an A-D-A-D-A structure and BT unit has been designed and synthesized.•A PCE of 3.07% was achieved for this molecule based photovoltaic device.•Different from other previous small molecules, annealing improve significantly the PCE.A solution processable A-D-A-D-A structure small molecule DCAEH5TBT using a BT unit as the core has been designed and synthesized for application in BHJ solar cells. The device employing DCAEH5TBT/PC61BM as active layer shows PCE of 2.43% without any post treatment. After thermal annealing (150 °C, 10 min), the PCE of this molecule based device increased to 3.07%, with Jsc of 7.10 mA/cm2, Voc of 0.78 V and FF of 55.4%, which indicates that high performance of solution processed small molecule based solar cells can be achieved using thermal annealing by carefully design molecule structure.Graphical abstractA small molecule DCAEH5TBT with an A-D-A-D-A structure and BT unit as the core has been designed and synthesized for application in BHJ solar cells. The PCE of this molecule based device increased from 2.43% to 3.07% after thermal annealing at 150 °C for 10 min.