Flexible and Stretchy Organic Photodetectors for Wearable Sensing <sup>†</sup>
Annotatsiya
Comprehensive Summary Photodetectors (PDs) are core components in imaging, health monitoring and environmental sensing systems. As electronics become increasingly integrated into wearable, soft and bio‐interfacing platforms, there is growing demand for photodetectors that combine mechanical stretchability, low power consumption and optical sensitivity. Unlike strain‐accommodating strategies using serpentine metal traces or rigid islands, intrinsically flexible and stretchable photodetectors are constructed from fully deformable active layers, electrodes and substrate. This ensures seamless mechanical conformity and long‐term biomechanical compatibility, enabling stable light detection even under stretching, bending, or twisting, thereby meeting the requirements of on‐skin, soft robotic, and subdermal applications. Recent advances in materials design, from stretchable conjugated polymers to conductive, deformable electrodes, have greatly improved the performance and durability of OPDs. Meanwhile, progress in device engineering, including solution‐based processing, scalable fabrication, and array integration, has facilitated the construction of high‐resolution stretchable photodiode arrays for multimodal sensing. These innovations collectively broaden the functional landscape of OPDs. This article highlights recent innovations in flexible and stretchable organic photodetectors, focusing on material design, morphology control, fabrication strategies, and emerging applications in wearable optoelectronics. Particularly, we analyze how molecular engineering approaches enhance both mechanical compliance and optoelectronic properties, discuss manufacturing techniques that enable scalable production, and highlight implementation examples in health monitoring, artificial vision, and human‐machine interfaces. Finally, we address key challenges and future research directions, including the development of sustainable processing methods, the creation of next‐generation wearable optoelectronic systems with enhanced functionality, and the establishment of standardized measurement protocols for accurately characterizing the performance of stretchable OPDs under operational conditions. Key Scientists Rogers and co‐workers first adhered photodetectors to human skin, introducing the concept of epidermal electronics. [1] Building on this vision, Someya's group in 2018 fabricated self‐powered ultraflexible sensors capable of conforming not only to the skin but also to dynamic organs such as the heart. [11] In 2021, they further integrated multiple photodiodes to realize a self‐powered photoplethysmography (PPG) sensor. [47] In parallel, Kippelen and colleagues in 2020 employed the conventional poly(3‐hexylthiophene‐2,5‐diyl) (P3HT): Indene‐C60 bisadduct (ICBA) active layer system to fabricate large‐area flexible OPDs, achieving performance comparable to silicon photodetectors in all aspects except response time. [10] In 2022, Yu et al. proposed an innovative device fabrication strategy in which the photoactive film formed a micromesh structure, thereby enhancing intrinsic stretchability without compromising electrical performance. [13] In the following year, an elastomer–semiconductor–elastomer stacked configuration was reported, enabling stretchable OPDs suitable for imaging applications. [58] Progress continued in 2024, Lin et al. utilized colloid processing to realize high‐performance flexible OPDs, demonstrating superior in‐situ detection of trace pollutants in water. [60] In 2024, Huang's group regulated the molecular ordering of small‐molecule acceptors to extend OPD applications to large‐area flexible devices and by 2025 advanced molecular engineering of acceptors to further broaden the application space of flexible OPDs across diverse fields. [18‐19] Chen's group in 2024 significantly advanced the optical communication application of flexible OPDs by introducing a narrow‐band acceptor. [56] In the following year, relying on high‐performance flexible visible‐blind near‐infrared organic photodetectors, a flexible photonic contactless human‐machine interface has been developed, which significantly expands the applications of flexible OPDs. [80]