abstract
Novel C-60 and C70N-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 C-70 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 C-70 derivatives. These results help to understand how new fullerene acceptors can affect the performance of OPV devices.
keywords
OPEN-CIRCUIT VOLTAGE; FULLERENE DERIVATIVES; ELECTRON-ACCEPTORS; PHOTOVOLTAIC CELLS; BIS-ADDUCTS; PERFORMANCE; MORPHOLOGY; PCBM; EFFICIENT; ENERGY
subject category
Materials Science
authors
Gaspar, H; Figueira, F; Strutynski, K; Melle-Franco, M; Ivanou, D; Tome, JPC; Pereira, CM; Pereira, L; Mendes, A; Viana, JC; Bernardo, G
our authors
Flávio Alberto da Silva Figueira
Junior Researcher
Karol Strutyński
Assistant Researcher
Manuel Melle-Franco
Principal Researcheracknowledgements
This work was partially funded by National Funds through FCT-Portuguese Foundation for Science and Technology, Reference UID/CTM/50025/2019 and FEDER funds through the COMPETE 2020 Programme under the project number POCI-01-0145-FEDER-007688 (i3N). Thanks are also due to FCT/MEC for the financial support to QOPNA (FCT UID/QUI/00062/2019), CICECO-Aveiro Institute of Materials (FCT UID/CTM/50011/2019), CQE (FCT UID/QUI/0100/2019) and CIQUP (FCT UID/QUI/UI0081/2019) research units, through national funds and where applicable co-financed by the FEDER, within the PT2020 Partnership Agreement. This work was also financially supported by project UID/EQU/00511/2019-Laboratory for Process Engineering, Environment, Biotechnology and Energy-LEPABE funded by national funds through FCT/MCTES (PIDDAC). H.G. thanks Fundacao para a Ciencia e a Tecnologia (FCT) for his PhD scholarship (SFRH/BD/103009/2014). The research contracts of F.F. (REF. -168-89-ARH/2018) is funded by national funds (OE), through FCT-Fundacao para a Ciencia e Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19. M.M.-F. acknowledges also support from FCT under the project IF/00894/2015.