Air Stability of Organic Thin-Film Transistors with Thiol-Functionalized Gold Bottom Source and Drain Contacts

The contact resistance and the intrinsic channel mobility of p-channel and n-channel organic thin-film transistors (TFTs) based on four different vacuum-deposited small-molecule semiconductors are monitored while the TFTs are stored in ambient air. The TFTs are fabricated in the inverted coplanar (bottom-gate, bottom-contact) device architecture, and the gold contact surface is functionalized using thiols. The initial contact resistance of all TFTs is quite small, between and 125 and 450 Ωcm, but it degrades quite rapidly over a span of 150 h, by 43% to 500%, depending on the semiconductor. Simultaneously, the intrinsic channel mobility degrades only slightly (between 11% and 50%), indicating that device degradation occurs primarily at the contact-semiconductor interface. Across all investigated parameters, DPh-DNTT is found to yield the most air-stable TFTs among the semiconductors investigated here.