Interface engineering for improving optical switching in a diarylethene-channel transistor

Photochromic diarylethene (DAE) molecules were employed as the channel layer of a field-effect transistor, where the drain current was effectively modulated by the reversible phase transition between a semiconductor (closed-ring) and an insulator (open-ring) under ultraviolet or visible light irradiation. Our goal was the further improvement of optical switching properties by interface engineering. First, we reduced the hole injection barrier by introducing an α-sexithiophene (6T) thin film at the interface between the source-drain electrodes and the DAE channel layer. As a result, the threshold voltage of the DAE-FETs was greatly reduced from-64 to-4 V. Second, we improved the optical switching performance by the surface treatment of a SiO₂ gate insulator with poly(methyl methacrylate) (PMMA). The drain current was unchanged even after 10 cycles of optical switching in contrast to the rapid degradation found with untreated DAE transistors. The combination of these improvements and interdigitated source-drain electrodes eventually resulted in a light irradiation driven on/off ratio of over 10³. Significantly, the light-induced on/off ratio was comparable to that driven by an electrical field, which satisfies the requirement for industrial optical applications. Our findings will provide useful ways of realizing high-performance optical switching transistors.