PffBT4T-2OD Based Solar Cells with Aryl-Substituted N-Methyl-Fulleropyrrolidine Acceptors

Abstract

Novel C60 and C70 N-methyl-fulleropyrrolidine derivatives, containing both electron withdrawing and electron donating substituent groups, were synthesized by the well-known Prato reaction. The corresponding highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy levels were determined by cyclic voltammetry, from the onset oxidation and reduction potentials, respectively. Some of the novel fullerenes have higher LUMO levels than the standards PC61BM and PC71BM. When tested in PffBT4T-2OD based polymer solar cells, with the standard architecture ITO/PEDOT:PSS/Active-Layer/Ca/Al, these fullerenes do not bring about any efficiency improvements compared to the standard PC71BM system, however they show how the electronic nature of the different substituents strongly affects the efficiency of the corresponding organic photovoltaic (OPV) devices. The functionalization of C70 yields a mixture of regioisomers and density functional theory (DFT) calculations show that these have systematically different electronic properties. This electronic inhomogeneity is likely responsible for the lower performance observed in devices containing C70 derivatives. These results help to understand how new fullerene acceptors can affect the performance of OPV devices.

Thiophene- and Carbazole-Substituted N-Methyl-Fulleropyrrolidine Acceptors in PffBT4T-2OD Based Solar Cells

“…This became particularly evident when preparing concentrated fullerene solutions (~20 mg•mL −1 ) for 13 C NMR analysis-while all the C 70 derivatives were soluble or partially soluble in deuterated chloroform CDCl 3 (C 70 bearing the carbazole unit showed to be a little less soluble), the C 60 derivatives were not soluble in CDCl 3 , and could be completely solubilized only in CS 2 (the most powerful solvent for fullerenes). This higher solubility of C 70 derivatives in organic solvents, compared to the corresponding C 60 derivatives, has been previously reported [54,55]. The 1 H NMR spectra of the C 60 derivatives are quite simple and shows the characteristic features of a N-methyl-(60)fulleropyrrolidine mono-adducts.…”

Graded Morphologies and the Performance of PffBT4T-2OD:PC71BM Devices Using Additive Choice

“…These properties, together with its tendency to form relatively pure polymer domains when blended with fullerene acceptors, allow it to perform well in an OPV device, when used in relatively thick bulk-heterojunction (BHJ) layers (~300 nm). PffBT4T-2OD has, therefore, been the subject of numerous OPV studies either blended with PC 71 BM [6][7][8][9][10][11][12][13] or with other fullerenes [5,[14][15][16].…”