Enhanced Performance of Polymer Field-Effect Transistors via Substitutional Doping Performed Using Blended Polymer Films

The doping process performed using small conjugated-molecules or polymers remains a formidable challenge in organic electronics owing to the inherent instability caused by uncontrolled dopant diffusion and volatility. In this study, we propose a novel approach to address this issue using the substitutional doping of molecular moieties by blending a homopolymer and a donor–acceptor type conjugated copolymer. The resulting blended polymer film served as the active layer for the fabrication of a polymer field-effect transistor (PFET). Poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) was used as the matrix semiconductor material, whereas poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno[3,2-b]thiophene)], with alternating electron-accepting diketopyrrolopyrrole (DPP) moieties and the BTTT unit along the polymer backbone, was used as the DPP molecular dopant. The PFET based on the pristine PBTTT channel layer exhibited field-effect mobility of only 0.010 cm²/Vs. However, the mobility significantly improved to 0.108 cm²/Vs when the ratio of the DPP moieties was gradually increased in the blended channel. Additionally, the turn-on voltage shifted in the positive direction, ranging from 17.5 V to a maximum value of 26.4 V. Therefore, our systematic analytical investigation of the PBTTT films doped with substitutional DPP moieties indicates that the blending process induces the charge transfer of holes from the DPP moiety to the PBTTT films, thereby enhancing the overall performance of the PFET.