Noise Suppression in Organic Photodiodes: A Comprehensive Review of Mechanistic Insights and Design Principles

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.