Protonated Organic Semiconductors: Origin of Water-Induced Charge-Trap Generation

Despite dramatic improvements in the electronic characteristics of organic semiconductors, the low operational stability of organic field‐effect transistors (OFETs) hinders their direct use in practical applications. Although the literature contains numerous reports on the effects of water on the operational stability of OFETs, the underlying mechanisms of trap generation induced by water remain unclear. Here, a protonation‐induced trap generation of organic semiconductors is proposed as a possible origin of the operational instability in organic field‐effect transistors. Spectroscopic and electronic investigation techniques combined with simulations reveal that the direct protonation of organic semiconductors by water during operation may be responsible for the trap generation induced by bias stress; this phenomenon is independent of the trap generation at an insulator surface. In addition, the same feature occurred in small‐bandgap polymers with fused thiophene rings irrespective of their crystalline ordering, implying the generality of protonation induced trap generation in various polymer semiconductors with a small bandgap. The finding of the trap‐generation process provides new perspectives for achieving greater operational stability of organic field‐effect transistors.