Synthesis And Application Of Fullerene C₆₀ Derivatives In Organic Solar Cells

Polymer solar cells (PSCs) have attracted more and more attention in thelast several years, due to their virtues of low cost, simple fabrication, light weightand flexible use in practice. But the low power conversion efficiency (PCE) andstability of the devices have limited the development of polymer solar cells.There is still a long way to go to fulfill the goal of commercialization. It isimportant to improve the performance of PSCs to synthesize new fullerenederivates and investigate their structure-property relationships.Herein, we synthesized two new fulleropyrrolidine derivatives which weresubstituted with single (EHIHC60P) and double indoles (DEHIC60P) groupsthrough the Patro reaction. The performance of the fullerene derivatives werecharacterized by UV–visible absorption,1HNMR,13C NMR and MALD-TOF.The energy levels of these derivatives were studied by the Cyclic Voltammetry.The LUMO energy levels EHIHC60P and DEHIC60P are-3.65and-3.60ev,which are0.08and0.13ev higher than that of PCBM (-3.73ev), respectively.Besides, it is obvious that the absorption intensity of EHIHC60P and DEHIC60Pare much stronger than that of PCBM at the same concentration. Whenfabricating the solar cells various blend ratios of donor (P3HT) to acceptor,additives and different annealing temperatures were all compared. The uppermostPCEs of3.32%and3.23%were obtained for P3HT:EHIHC60P andP3HT:DEHIC60P based solar cells at the composited ratio of1:1after the activelayers were annealed at150℃under inert atmosphere，with a open-circuitvoltage (Voc) of0.66V and0.74V, respectively. For comparison, the devicebased on P3HT: PC61BM at the same conditions showed the PCE of3.28%, witha Voc of0.61V. The influence on the photovoltaic performances were comparedand discussed. CN and DIO were used as processing cosolvent additives, which had significant effect on the morphology of the active layers. However, noobvious changes on the photo voltaic performance were observed, which wasprobably due to the enhancement surface roughness of the active layer and thusthe charge collection decreased. More efforts to develop highly efficientacceptors based on indole-containing fulleropyrrolidine derivatives are currentlyon going in our group.