(E)-1,2-Di(thiophen-2-yl)ethene based high mobility polymer for efficient photovoltaic devices without any post treatment

In order to investigate the effect of an (E)-1,2-di(thiophen-2-yl)ethene (TVT) unit on the hole mobility and photovoltaic properties of dithienyl-difluorobenzothiadiazole (DTBT) based polymers, two conjugated polymers PDT-DTBT-DT (thiophene backboned) and PTVT-DTBT-DT (TVT backboned) were synthesized. Compared to PDT-DTBT-DT, the backbone conformation of PTVT-DTBT-DT could be well modulated by the TVT unit, leading to an extended conjugation length and strengthened intermolecular interaction. Interestingly, it's found that the ultraviolet-visible (UV-vis) absorption peaks of the PTVT-DTBT-DT film was blue-shifted compared to that of the solution. The organic field-effect transistor (OFETs) characterization showed that PTVT-DTBT-DT possessed a high hole mobility of 0.12 cm² V^-1 s^-1, which was higher than that of the counterpart PDT-DTBT-DT (0.04 cm² V^-1 s^-1). Through simplified device optimization without any additives and annealing treatment, a power conversion efficiency (PCE) of 7.86% was achieved for PTVT-DTBT-DT with a short-circuit current density (J_sc) of 16.33 mA cm^-2 and a fill factor (FF) of 68.92%, which is higher the PCE of 7.29% of PDT-DTBT-DT with a J_sc of 15.60 mA cm^-2 and a FF of 66.62%. The PCE of 7.86% is among the highest PCEs reported for devices fabricated without any additives and thermal annealing treatment. The results revealed that PTVT-DTBT-DT as an ideal conjugated polymer could provide a greater possibility for the commercial application of PSCs, especially in terms of low cost and manufacturing convenience.