Diarylmethanofullerene: Efficient Polymer Solar Cells with Low-Band-Gap Copolymer

The photovoltaic performance of the polymer bulk heterojunction solar cells based on the low-band-gap D–A copolymer P as donor and modified fullerene (modi-PC60BM) as acceptor was in. We have achieved power conversion efficiency (PCE) of ∼2.35% for a polymer solar cell with modi-PC60BM as an electron acceptor in bulk heterojunction active layer, which is higher than that for PC60BM counterpart (1.50%). The increase in the PCE has been attributed to the increase in absorption in visible and higher LUMO level of modi-PC60BM, resulting in enhancement in J sc and V oc, respectively. In the device fabrications, we studied the effect of the solvent additive and modified PEDOT:PSS as a hole transport layer. The PCE of the polymer solar cell was improved up to 3.63% when the P:modi-PC60BM active layer was processed with the addition of CN as an additive in the THF solution (CN/THF), which is mainly attributed to more balanced charge transport due to the increased crystallinity of P in the blend. The PCE of polymer solar cell based on the active layer processed from CN/THF has been further improved up to 4.73% when a modified PEDOT:PSS (acetone-treated) was used as the hole transport layer. This increase in the PCE is mainly due to the enhancement in J sc and FF and may be attributed to the improvement in the conductivity induced by the polar solvent with high dipole moment, leading to more efficient collection of charge carrier by the anode.