A new 2D-conjugated small molecule with alkylthio-thienyl-conjugated side chains (BDTT-S-TR) is synthesized for application as a donor material in organic solar cells (OSCs). The OSCs based on BDTT-S-TR/PC70 BM demonstrate a power conversion efficiency (PCE) of 9.20% without extra treatment. Moreover, an encouraging PCE of 6.68% is achieved from the device with active area of 144 mm(2).