Bridging Performance Gaps in Organic Photodetectors: A Critical Review of Metal-Semiconductor-Insulator-Metal (MSIM) Architectures, Charge Dynamics, and Device Stability.

Organic photodetectors (OPDs) have emerged as promising candidates for next-generation optoelectronic technologies owing to their mechanical flexibility, lightweight nature, low-cost fabrication, and spectral tunability. Despite significant progress, conventional OPD architectures, including photoconductors, phototransistors, photomultiplication devices, metal-semiconductor-metal (MSM) photodetectors, and photodiodes, continue to face challenges such as high dark current, limited charge-carrier mobility, strong exciton binding energy, and operational instability, which restrict their application in ultrafast and weak-light detection. Recently, metal-semiconductor-insulator-metal (MSIM) photodetectors have emerged as a promising alternative, offering fundamentally distinct operating principles based on displacement-current generation and interfacial capacitive charge modulation rather than conventional steady-state drift-diffusion transport. This review provides a comprehensive overview of recent advances in MSIM photodetectors, focusing on device architectures, interfacial charge dynamics, dielectric engineering, and transient photoresponse mechanisms. Particular attention is devoted to the role of solid dielectric layers, ionic liquids, and ionic liquid gels in suppressing dark current, enhancing interfacial charge modulation, and improving transient photocurrent generation. Furthermore, applications ranging from sensing to advanced optical communication, are systematically analyzed. Finally, current challenges and future research directions are discussed, emphasizing the potential of advanced MSIM architectures to achieve reduced dark current, tunable transient responses, enhanced interfacial control and multifunctional photodetection capabilities for next-generation optoelectronic technologies.