Synthesis and studies of methyl ester substituted thieno-o-quinodimethane fullerene multiadducts for polymer solar cells

A new series of fullerene (C60) multiadducts of methyl ester substituted thieno-o-quinodimethane were synthesized for polymer solar cells (PSCs). The synthesized 5-methyl ester thieno-o-quinodimethane fullerene (C60) multiple adducts, such as METFMA (mono-adduct), METFBA (bis-adduct) and METFTA (tris-adduct), showed good solubility in toluene, CHCl3 and ODCB. Their molecular structures were confirmed by 1H, 13C NMR, UV–visible spectroscopy, DSC, TGA and HRMS Cyclic voltammetry revealing a lowest unoccupied molecular orbital (LUMO) energy level of −3.65 eV for METFMA, −3.53 eV for METFBA and −3.42 eV for METFTA, which is higher than that of PC61BM. The higher LUMO energy level of METFMA, METFBA and METFTA resulted in an enhancement of the open-circuit voltages (Voc) of PSCs. Device of the multiple adduct acceptors was blended with a P3HT donor with the configuration, ITO/PEDOT/P3HT:acceptor/LiF/Al, using METFMA, METFBA, METFTA and PC61BM as the electron acceptor. The optimal photovoltaic performances were achieved using METFBA and METFTA with power conversion efficiencies of 3.00% and 2.93%, respectively. These results were comparable to the device conducted with P3HT:PC61BM (3.42%) under the same conditions.