Flexible and wearable WSe₂ optoelectronics: current progress, technological challenges, and future directions

Tungsten diselenide (WSe₂), a prominent member of the two-dimensional (2D) transition metal dichalcogenide (2D-TMDC) family, has attracted significant attention for next-generation flexible and wearable optoelectronic applications owing to its tunable bandgap, excellent carrier transport characteristics, strong light-matter interaction, and superior mechanical flexibility. Recent advancements in heterostructure engineering, composite formation, and sustainable device fabrication have considerably enhanced the performance of WSe₂-based photodetectors and multifunctional electronic devices. In particular, the integration of WSe₂ with paper substrates has emerged as a promising strategy for developing lightweight, low-cost, biodegradable, and electronic systems with potential environmental advantages associated with biodegradable substrates and low-complexity fabrication. This review comprehensively summarizes recent progress in WSe₂ heterostructures and composites fabricated on flexible substrates for flexible and wearable optoelectronics. The fundamental properties of WSe₂, material synthesis routes, electrode fabrication techniques, and heterostructure design strategies are critically discussed. Particular emphasis is placed on the role of interface engineering, defect modulation, doping methods, and hybrid material integration in improving responsivity, detectivity, response speed, and mechanical durability. Furthermore, recent developments in paper-based photodetectors, wearable sensing platforms, self-powered devices, and intelligent optoelectronic systems are systematically assessed through performance benchmarking and comparative analysis. Present challenges associated with material quality, device stability, large-scale manufacturing, and commercialization are highlighted, together with emerging opportunities in sustainable electronics, Internet of Things (IoT) technologies, artificial intelligence-assisted sensing, and next-generation wearable systems. By giving a critical assessment of recent advances and future research directions, this review serves as a valuable resource for the development of high-performance, flexible, and environmentally responsible WSe₂-based optoelectronic technologies.