Light-induced bias stress reversal in polyfluorene thin-film transistors

Gate bias-stress effects in the high-performance semiconducting polymer poly-9,9′ dioctyl-fluorene-co-bithiophene (F8T2) were studied. The bias stress in F8T2 was characterized in devices having various gate dielectric materials—different types of SiO2 and a polymer—and a variety of chemically modified dielectric/semiconductor interfaces. A bias-stress effect was reversed by illuminating the transistor structure with band gap radiation. The recovery rate was directly related to the absorption characteristics of F8T2. We conclude that bias stress in F8T2 is due to hole charge trapping inside the polymer, close to the dielectric interface and not to a structural change in the polymer, or to charge in the dielectric.