The performance of polymer solar cells based on poly [N-900-hepta-decanyl-2,7- carbazolealt- 5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) made at the rotation speed of 1000∼3000 rpm was studied. The structure of device is Indium Tin Oxide (ITO)/molybdenum oxide (10 nm)/PCDTBT: PC71BM (1000∼3000 rpm)/2,9- dimethyl-4,7- diphenyl-1,10-phenanthroline (10 nm)/aluminum. The maximum power conversion efficiency of the device is obtained at a rotation speed of 2000 rpm, which is attributed to reach the optimal balance between the light absorption and the carrier collection efficiency. In addition, the different sheet resistances of ITO were used as substrate to find out which is appropriate for the organic solar cell application. The result showed that the device using 15 Ω/sq of ITO as substrate has a better efficiency than that of the device using 7 Ω/sq of ITO. It is due to the transmittance of ITO (15 Ω/sq) being higher than that of ITO (7 Ω/sq), especially from 350 nm to 475 nm, that leads to the efficiency of the device (2000 rpm) improving from 3.84% to 4.25%.