Gyeong Min Lee, Tae Hyuk Kim, Yunsang Kim, Jae Won Shim
Abstract Organic photodiodes (OPDs) are emerging as leading candidates for next‐generation image sensors owing to their tunable photophysical properties, which enable broadband detection from the visible to X‐ray regimes and open new possibilities for intelligent systems such as fingerprint sensing, gesture recognition, and medical imaging. Across these applications, minimizing the dark current density ( J d ) is of paramount importance, as it sets the noise floor, while thermal and low‐frequency noises further depend on the shunt resistance and trap dynamics, thereby constraining the signal‐to‐noise ratio, dynamic range, and specific detectivity ( D * ). This review elucidates the microscopic origins of J d by distinguishing two universal leakage channels: bulk thermal generation via mid‐gap or tail‐state traps and field‐assisted carrier injection through interfacial barriers. It further clarifies how these mechanisms define the shot and thermal noise limits that constrain sensitivity. Beyond white‐noise considerations, this work discusses low‐frequency (1/ f ) noise, whose origins in organic semiconductors remain debated yet critically impact stability and D * . Within this framework, recent progress is surveyed in active‐layer design, disorder management, and interlayer engineering. By benchmarking strategies against unified figures of merit, a roadmap toward sub‐femtoampere J d , suppressed noise, and enhanced D * is charted, highlighting key material challenges and architectural opportunities for future commercial systems.