Effect of the molecular weight of poly(3-hexylthiophene) on the morphology and performance of polymer bulk heterojunction solar cells

The morphology and performance of bulk heterojunction solar cells comprised of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C(61)butyric acid methyl ester (PCBM) have been investigated using P3HT with different molecular weights (MWs). It is concluded that the optimum annealing temperature for the bulk heterojunction material is related to the MW of P3HT. The best performance is obtained by using P3HT with an optimum ratio between high MW and low MW components. The corresponding 'ideal morphology' is comprised of highly ordered crystalline regions formed by low MW P3HT embedded and interconnected by a high MW P3HT matrix.