Unmixed Planar Heterojunction Interfaces Enabling Exceptional Air Stability in Organic Photodetectors

It is proposed organic photodetectors (OPDs) with immiscible planar heterojunction (PHJ) interfaces can address the air stability challenges of bulk heterojunction (BHJ) and pseudo-PHJ OPDs, which suffer from nanomorphology instability. A random polythiophene (RP-T50) containing ≈50 mol% thiophene units with thermocleavable side chains (TCSs) is employed as the electron donor, while [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) served as the electron acceptor. Thermal annealing of RP-T50 (RP-T50-COOH) thin films cleaved the TCSs, rendering the films insoluble and forming a stable, unmixed interface with PC₇₁BM. This approach prevented the formation of partially mixed pseudo-PHJ interfaces that compromise air stability in conventional PHJ OPDs. The insoluble RP-T50-COOH thin films enabled all-green-solvent processing, resulting in high performance, including a responsivity of ≈138 mA W⁻¹, a specific detectivity of ≈1.68 × 10¹² Jones, and a linear dynamic range of ≈100 dB without external bias. Notably, the devices exhibited exceptional air stability, maintaining performance for ≈250 days in ambient storage without encapsulation. These findings demonstrate a simple and scalable strategy for enhancing OPD stability, paving the way for their commercial application across diverse fields.