Synergistic Thin-Film Alignment and Surface Passivation for Anisotropic Charge Transport and Long-Term Stability in OFETs

Abstract

Organic field-effect transistors (OFETs) based on conjugated polymers are promising for flexible, low-cost electronics

however, their performance is often limited by interfacial trap states and disordered molecular packing. In this work, the combined influence of fabrication method (spin coating and UFTM), dielectric interface engineering (OTS and CYTOP), and molecular orientation on the charge transport characteristics of poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2)-based thin film transistors is systematically investigated. The UFTM process produces highly aligned polymer films, yielding pronounced optical anisotropy with a dichroic ratio of ~ 6.5 at an optimized annealing temperature of 120 °C. The optimized UFTM CYTOP (ǁ) device exhibits a maximum field-effect mobility of ~2.8 × 10-3 cm2 V-1 s-1, an on/off current ratio of ~ 4 × 106, improved threshold voltage, reduced subthreshold swing, excellent device-to-device reproducibility, while retaining ~ 80% of its initial mobility after 60 days under ambient conditions. These findings demonstrate a simple, low-cost, and scalable fabrication strategy for improving the electrical performance and operational reliability of F8T2-based OFETs. © 2001-2011 IEEE.