Abstract:

Polycrystalline organic semiconductor thin films have attracted increasing interest because of their high charge-carrier mobility and low-cost solution processability. However, their electrical performance is highly sensitive to ambient humidity, which severely limits long-term device stability. To address this challenge, this study systematically examines the influence of ambient moisture on the electrical characteristics of organic field-effect transistors (OFETs) based on small-molecule organic semiconductor/polystyrene-blended polycrystalline thin films. The results demonstrate that ambient moisture plays a dual role in device operation. On one hand, water molecules preferentially accumulate at grain boundaries and at the semiconductor/dielectric interface, where they act as defect sources that introduce additional trap states, leading to a gradual reduction in carrier mobility and a positive shift in threshold voltage. On the other hand, the polarization effect associated with the high dielectric constant of moisture enhances channel carrier modulation, resulting in a temporary increase in current response. Nevertheless, this polarization process is inherently dynamic, ultimately leading to pronounced fluctuations in device parameters and long-term electrical instability. To mitigate moisture-induced degradation, molecular dopants were introduced as a strategy for structural regulation and interface stabilization. Although the incorporation of 1% dopant reduces grain size and slightly compromises initial device performance, it effectively passivates grain-boundary defects and significantly suppresses the formation of moisture-related trap states. Consequently, device stability under ambient conditions is substantially enhanced, with both carrier mobility and threshold voltage remaining stable after prolonged air exposure. This study elucidates the fundamental role of ambient moisture as both a “trap-inducing source” and a “polarization medium” in polycrystalline OFETs, and proposes a simple yet effective molecular doping strategy for achieving high-performance, environmentally stable polycrystalline OFETs.

Key words: organic field-effect transistors, polycrystalline thin films, water-induced polarization, F₄TCNQ doping, environmental stability