Small-molecule vinazene acceptors for bulk heterojunction organic photovoltaics

This paper reports the synthesis and characterization of a new vinazene-based small molecule, 4,7-bis(2-(1-(2-ethylhexyl)-4,5-dicyanoimidazol- 2-yl) vinyl)diketopyrrolopyrrole (EV-DPP). The known vinazene-based small molecule, 4,7-bis(2-(1-(2-ethylhexyl)-4,5-dicyanoimidazol-2-yl)vinyl)benzo[c][1, 2,5]thiadizole (EV-BT), was also prepared for comparison. The benzothiadiazole unit in EV-BT was replaced with a DPP unit in EV-DPP because DPP units are strong absorbing chromospheres. The UV absorption maxima of EV-DPP film (λ _max = 386, 573 nm) were greatly red shifted compared to the maxima of EV-BT film (λ _max = 337, 444 nm). Our preliminary device work showed the possibility of the use of EV-DPP as an electron acceptor in OPVs. The P3HT: EV-DPP film showed a better power conversion efficiency of 0.02% compared to P3HT: EV-BT due to the preferable UV absorption characteristics of EV-DPP.