Nanomorphology of PCDTBT:PC70BM Bulk Heterojunction Solar Cells

The nanomorphology of a bulk heterojunction (BHJ) material constructed from poly[N ‐ 9′‐hepta‐decanyl‐2,7‐carbazole‐ alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT):[6,6]‐phenyl C70‐butyric acid methyl ester (PC70BM) is shown to be laterally oriented, in contrast to the column‐like morphology of the similar poly(3‐hexyl thiophene):PC60BM. The lateral orientation in the PCDTBT:PC70BM BHJ is not ideal for sweeping charge out at the electrodes. As a result, the power conversion efficiency decreases as the thickness of the BHJ active layer is increased.