Synergetic Enhancement of Device Efficiency in Poly(3-hexylthiophene-2,5-diyl)/[6,6]-phenyl C61Butyric Acid Methyl Ester Bulk Heterojunction Solar Cells by Glycerol Addition in the Active Layer

Poly(3-hexylthiophene-2,5-diyl)(P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) is the widely used active layer for the bulk heterojunction solar cells. Annealing is essential for P3HT:PC60BM active layer, since it facilitates the creation of better network for the transfer of the charge carriers. However, the PC60BM in the active layer can crystallize excessively during annealing treatments and disrupt the favorable morphology by forming crystallites in micrometer ranges, thus reducing device efficiency. In this paper we used glycerol as an additive in the active layer. Due to high boiling point of glycerol, it makes slow drying of the active layer possible during the annealing. It thus gives enough time to both electron donor (P3HT) and electron acceptor (PC60BM) components of the active layer to self-organize and also restrict the crystal overgrowth of PC60BM. Further, the glycerol additive makes the active layer smoother, which may also improve adhesion between the electrode and the active layer. The devices with the pristine active layer showed a power conversion efficiency (PCE) of about 2.1% and, with the addition of 30 vol% of glycerol in the active layer, the PCE value increased to 3%.