Improving Process Compatibility of Multilayer Organic Fiber Photodetectors by Combining Coaxial Thermal Evaporation with Dip‐Coating

Abstract Fiber photodetectors (FPDs) are promising candidates for wearable applications due to their flexibility, knittability, and full‐angle detection. The current state‐of‐the‐art FPDs based on inorganic photosensitive materials show drawbacks in mechanical flexibility. The organic FPDs (OFPDs) are superior, while the fabrication is limited by multi‐layer process compatibility issues. Herein, a diode‐type five‐layer OFPD with Zn/ZnO/PBDB‐T:ITIC‐Th/MoO₃/PEDOT:PSS structure is prepared by combining thermal evaporation with a successive dip‐coating method. It is worth mentioning that the uniform coaxial MoO₃ interfacial layer is processed by the proposed fiber‐compatible thermal evaporation technique, while the other functional layers are enabled by the solution‐based dip‐coating method. At the bias of −0.5 V, the optimized OFPD exhibits a dark current density of 8.46 × 10⁻⁸ A cm⁻², a responsivity of 86.4 mA W⁻¹ (@ 760 nm), and a specific detectivity of over 10¹¹ Jones in the visible range of 400–760 nm. Besides, the device displays a fast response speed of 0.44 and 0.14 ms for rise and fall time, showing the capability of full‐angle detection. The device is demonstrated in photoplethysmography for real‐time heart‐rate monitoring, suggesting its potential for practical application in wearable electronics.