Advancements and Challenges of Vacuum-Processed Organic Photodiodes: A Comprehensive Review

Organic photodiodes (OPDs) have made remarkable strides and now poised to surpass traditional silicon photodiodes (PDs) in various aspects including linear dynamic range (LDR), detectivity, wavelength selectivity, and versatility.^[1] Tunable mechanical and optoelectronic properties of organic semiconductors, coupled with lower process costs, have propelled OPDs into the spotlight across fields such as wearable light fidelity systems, flexible image sensors, and biomedical imaging.^[2–5] While most advanced organic imaging systems to date rely on polymer-based solution processes, challenges such as the use of toxic organic solvents and reproducibility issues hinder their commercialization.^[6,7] Vacuum-processed OPDs offer a promising alternative, boasting eco-friendliness and compatibility with large-scale fabrication facilities.^[8,9] In this review, recent advancements and challenges in vacuum-processed OPDs, an area that has received less attention compared to solution-processed counterparts, are explored. Herein, four primary pathways for development of vacuum-processed OPDs are outlined: 1) ultraviolet-selective OPDs, 2) visible-light-selective OPDs, 3) near-infrared or short-wave-infrared-sensitive OPDs, and 4) addressing challenges such as higher noise currents compared to inorganic PDs. In this review, it is aimed to furnish readers with a comprehensive understanding of vacuum-processed OPDs, spanning from materials design to device engineering.