The reason why a kind of diketopyrrolopyrrole‐analogue can act as acceptors: Theoretical study and characterization

• Published in: International journal of quantum chemistry 2018-12, Vol.118 (24), p.n/a
• Main Authors: Pan, Jie, Wang, Fei, Pan, Yi‐Qi, Xie, Yu‐Zhong, Sun, Guang‐Yan, Jin, Guang‐De
• Format: Article
• Language: English
• Subjects: bulk‐heterojunction; Charge injection; Chemistry; conversion of donor to acceptor; density functional theory; diketopyrrolopyrrole; Energy conversion efficiency; Energy levels; Molecular orbitals; organic solar cells; Physical chemistry; Quantum physics
• ISSN: 0020-7608; 1097-461X
• DOI: 10.1002/qua.25782

Recently, diketopyrrolopyrrole (DPP)‐based photovoltaic materials have been continuously modified to improve the power conversion efficiency (PCE). However, it was reported that 2,5‐Bis(2‐ethyl‐hexyl)‐3,6‐bis(5‐(benzofuran‐2‐yl)thiophen‐2‐yl)‐pyrrolo[3,4‐c]pyrrole‐1,4‐dione (BFT), composed of benzofuran‐connected DPP donor, exhibited a relatively low PCE. Besides, the analogue named 2,5‐Diethylhexyl‐3,6‐bis(5‐(benzofuran‐2‐yl)thiophen‐2‐yl)‐pyrrolo[3,4‐c]pyrrole‐1,4‐dithione (BFT‐SS), even showed a PCE lower than 0.001% when compounded with fullerene derivatives. The extremely low PCE could attribute to the low‐lying lowest unoccupied molecular orbital (LUMO) energy levels. Hence, in this article, we proposed that both BFT‐SS and its rotamer BFT‐SS’ with low LUMO energy levels could be converted as acceptors. And comparative analysis was demonstrated with the parent compound BFT and BFT’. The results highlight the effect of sulfur atom(S) in the thioketo groups could twist the molecules and reduce the LUMO energy level, thereby possess low the charge injection barrier and reorganization energy (λ), during the conversion of BFT‐SS and BFT‐SS’ from donor to acceptor. Finally, we sincerely expect the discussion to provide a meaningful idea for the development of acceptors. Diketopyrrolopyrrole (DPP)‐based small molecules generally consist of an adjacent aromatic substituent and π‐conjugated segments, whose optical and electronic properties can be easily modulated. Derivates BFT‐SS and its rotamer BFT‐SS’, both with low LUMO energy levels, can be converted from electron donor to acceptor when combined with PTB7‐Th.