Air-processable silane-coupled polymers to modify a dielectric for solution-processed organic semiconductors

Poly(styrene-r-3-methacryloxypropyltrimethoxysilane) (PSMPTS) copolymers were synthesized by the free radical polymerization of styrene and 3-methacryloxypropyltrimethoxysilane (MPTS) for use as surface modifiers. PSMPTS copolymers were spun-cast onto a hydrophilic SiO₂ layer and were then annealed at 150 °C in ambient air. The polystyrene (PS)-based copolymer, with a molecular weight of 32 700 g mol^-1 and approximately 30 MPTS coupling sites, was easily grafted onto the SiO₂ surface after annealing periods longer than 1 min, yielding a physicochemically stable layer. On the untreated and polymer-treated dielectrics, spin-casting of an ultrasonicated poly(3-hexyl thiophene) (P3HT) solution yielded highly interconnected crystal nanofibrils of P3HT. The resulting organic field-effect transistors (OFETs) showed similar mobility values of 0.01-0.012 cm² V^-1 s^-1 for all surfaces. However, the threshold voltage (V_th) drastically decreased from +13 (for bare SiO₂) to 0 V by grafting the PSMPTS copolymers to the SiO₂ surface. In particular, the interfacial charge traps that affect V_th were minimized by grafting the 11 mol % MPTS-loaded copolymer to the polar dielectric surface. We believe that this ambient-air-processable silane-coupled copolymer can be used as a solution-based surface modifier for continuous, large-scale OFET fabrication.