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.