Adjusted photovoltaic performance of tetrafluorobenzene-based small molecules by tailoring with different arm of acceptor units

Abstract

Three π-conjugated small molecules (SMs) with D(π-A-Ar)2 molecular frameworks are designed and synthesized as the donor materials in organic solar cells (OSCs). Containing tetrafluorobenzene (TFB) as central donor (D) core, thiophene as π-bridge, 2-octylthiophene (T) as terminal (Ar) unit, as well as the different arm of acceptor (A) units, pyridine-diketopyrrolopyrrole (PyDPP), thiophene-diketopyrrolopyrrole (TDPP) and isoindigo (IID), namely DTTFB(PyDPP-T)2, DTTFB(TDPP-T)2 and DTTFB(IID-T)2, respectively. The impacts of the different acceptor arms combined with the TFB core on the optical absorption, electrochemical property, hole mobility, film morphology, and solar cell performance were studied thoroughly. As a result, these SMs presented various light absorption properties, electrochemical performances, and hole mobilities, which are helpful to the optimization of short-circuit current (Jsc), open-circuit voltage (Voc) and fill factor (FF) properties, respectively. Especially, the DTTFB(TDPP-T)2 showed a relatively lower optical band gap of 1.53 eV, and also showed the best coplanarity among the three SMs, which help it to get a higher Jsc of 12.44 mA cm−2 and a higher FF of 59.50%, and resulting in obtaining a best power conversion efficiency (PCE) of 5.15% in the DTTFB(TDPP-T)2/PC71BM-based cells, which is about 2.8 and 1.6 times higher than that of DTTFB(PyDPP-T)2/PC71BM and DTTFB(IID-T)2/PC71BM based cells, respectively. Obviously, introducing different acceptor units as arms onto the D(π-A-Ar) type SMs could be a promising strategy for designing high-performance TFB-based linear molecular donor materials.