Deciphering the Crystallinity-Dependent Sensitivity of Charge Injection in n-Channel Organic Transistors: Reliable Characterization and Optimized Performance.

The performance and reliability of n-type organic field-effect transistors (OFETs) are strongly influenced by the interplay between semiconductor crystallinity and the metal/semiconductor interface. Here, we systematically investigate a series of diketopyrrolopyrrole (DPP)-based n-type polymers with identical backbones but varying side-chain architectures, resulting in varied long-range order. By comparing devices fabricated with conventional Au and low-work-function Al/Ti electrodes, we elucidate the synergistic effects of intrinsic polymer crystallinity and interfacial energetics on charge injection, transport, and operational stability. Temperature-dependent electrical measurements and trap analyses demonstrate that contact resistance, rather than intrinsic bulk transport, dominates the observed mobility differences between polymers of moderate and high crystallinity. Optimized Al/Ti contacts mitigate these interfacial limitations, enabling a transition from contact-limited to channel-limited transport and significantly improving environmental and operational stability. These findings establish a quantitative framework linking crystalline order, injection efficiency, and device reliability. This framework provides critical design guidelines for the evaluation and optimization of high-performance n-type organic semiconductors.