Enhancement of Open-Circuit Voltage by Using the 58-Silylmethyl Fullerenes in Small-Molecule Organic Solar Cells

摘要

The application of 58--1,4-bis(silylmethyl)[60]fullerenes, C-60(CH2SiMe2Ph)(CH2SiMe2Ar) (Ar=Ph and 2-methoxylphenyl for SIMEF-1 and SIMEF-2, respectively), in small-molecule organic solar cells with a diketopyrrolopyrrole donor (3,6-bis[5-(benzofuran-2-yl)thiophen-2-yl]-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione (DPP(TBFu)(2))) is demonstrated. With the 58--silylmethyl fullerene acceptor, SIMEF-1, the devices showed the highest efficiency of 4.57% with an average of 4.10%. They manifested an improved open-circuit voltage (1.03V) owing to the high-lying LUMO level of SIMEF-1, while maintaining a high short-circuit density (9.91mAcm(-2)) through controlling the crystallinity of DPP by thermal treatment. On the other hand, despite even higher open-circuit voltage (1.05V), SIMEF-2-based devices showed lower performances of 3.53%, owing to a low short-circuit current density (8.33mAcm(-2)) and fill factor (0.40) arising from the asymmetric structure, which results in a lower mobility and immiscibility.