Insights into water-resistant organic photodetectors with ultra-low noise currents for underwater applications

Organic photodetectors (OPDs) showcase decent potentials in environmental monitoring, medical imaging, biometric security, image sensors, and so forth.1,2,3,4,5 Compared with inorganic photodetectors, OPDs have attracted more attention in achieving lightweight soft devices with visible and short-wavelength infrared weak light detection due to inherent advantages of organic materials (e.g., low-cost, intrinsic flexibility, solution processibility, tunable optical bandgap, and high absorption coefficient), effectively extending their application scenarios under water.1 When OPDs are used, their outstanding performances satisfying sensing and water-resisting functions are highly demanded due to the weakened light signals and complex environmental conditions in water. Thus, developing novel OPDs that combine the excellent water resistance with ultra-low noise current (in) is of critical importance.

Herein, we aim to discuss comprehensive design strategies of organic photosensitive active layers and interface layers for water-resistant OPDs with ultra-low noise currents. This perspective will provide new insights into the development of unconventional high-performance OPDs well suited to emerging underwater applications.

Design strategies

Ensuring the water insensitivity of both photosensitive active layers and interface layers is essential for OPDs operating in water. However, the challenge in developing waterproof OPDs relies on implementing their water resistance while preserving high performance and good flexibility. Conventional approaches employing thick or rigid waterproof encapsulating layers inevitably limit the flexibility of OPDs and even reduce their performance. Moreover, interfacial toughening may create defects in the photosensitive active layers and interface layers to increase noise currents of OPDs remarkably. Insertion of hydrophobic intermediate layers with low surface energy can weaken interfacial adhesion within OPDs, allowing water penetration and subsequent delamination at weak interfaces. Therefore, it is imperative to develop high-performance OPDs with excellent water resistance and low noise currents suiting for underwater operation, through synergistically designing self-adhesive, colloid-processed, and/or vertical phase separation (VPS) polymer heterojunction structures as waterproof photosensitive active layers as well as crosslinked interface layers with tunable hole or electron transport.