Enhanced Environmental Stability of Organic Phototransistors via Dual-Functional Polymeric Encapsulation

Organic phototransistors (OPTs) hold strong potential for next-generation optoelectronic systems due to their mechanical flexibility and compatibility with low-cost, large-area fabrication. However, their practical deployment remains hindered by environmental instabilities─particularly degradation caused by moisture and high-energy light exposure in the blue and near-ultraviolet regions. In this study, we report an integrated, single-layer yet dual-functional polymeric encapsulation layer (DPEL) that simultaneously serves as a moisture barrier and an optical filter. Engineered with a helically ordered molecular structure, the DPEL selectively attenuates light near 430 nm, significantly mitigating photoinduced degradation while maintaining high transmittance for nonreflected light components. The encapsulated OPTs exhibited remarkable stability under both humidity and light stress, with minimal threshold voltage shifts─4 V under gate bias stress at 72% relative humidity and 3 V over 28 days of continuous exposure to 34% relative humidity and high-energy light─as well as a suppressed mobility degradation of 14%. Comparative studies confirm that the DPEL outperforms conventional encapsulation strategies by offering long-term protection against both photonic and environmental stressors. This work presents a practical and simple encapsulation approach for enhancing the reliability of organic electronic devices, providing a foundation for their integration into wearable sensors, neuromorphic vision platforms, and other environmentally sensitive optoelectronic systems.