Impact of Thermal Stress on Device Physics and Morphology in Organic Photodetectors

Organic photodetectors (OPDs) capable of detecting visible to near-infrared light provide a ubiquitous platform for emerging flexible and wearable electronics. In the process of implementing OPDs into a Si-based manufacturing process, organic semiconductors undergo ≥ 200 °C thermal stress, leading to the deterioration of photosensing capability. Here, we combine multiscale characterization and device physics to unravel the impact of thermal stress on the optoelectronics characteristics of PTB7-Th:non-fullerene acceptor blends (NFAs: SiOTIC-4F, COTIC-4F, CO1-4F, and CO1-4Cl). For as-cast devices, favorable intermixing and phase separation between PTB7-Th and the NFA facilitate charge generation and extraction. Reductions in the OPD performance after thermal annealing (200 °C for 5–120 min) are observed due to the morphological degradation, regardless of the NFA choice, but the reduction is more severe for the PTB7-Th:SiOTIC-4F blend. Thermally induced morphological changes are examined using atomic force microscopy, wide-angle X-ray scattering, and solid-state NMR spectroscopy. This study provides essential insights into morphology-driven deteriorations, which will help in developing structure–stability–performance relationships in high detectivity OPDs.