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.