Revealing the Effects of Inert Annealing on Low-Noise Near-Infrared Organic Photodetectors via Precise Trap and Noise Characterization.

The utilization of near-infrared (NIR) organic photodetectors (OPDs) holds considerable promise, primarily owing to their solution processability and flexibility characteristics. The recent reduction of dark current in the NIR-OPDs is critical for achieving high performance in OPDs using the narrow bandgap of the active layer. However, recent NIR-OPDs with excellent low-dark current exhibit measurement limitations, particularly regarding noise and trap measurements, which are crucial for evaluating specific detectivity and understanding the physics of the NIR-OPDs. This study comprehensively analyzes precise noise and trap measurements at varying inert annealing temperatures applied to the electron-transport layer. The optimized annealing process led to a high specific detectivity of 1.3 × 10 cm Hz W at 850 nm and a low trap density of 9.9 × 10 cm at a shallow-trap-energy level of 0.37 eV. The inert annealing process offers an example of typical issues, such as water-induced trap analysis. Our research explains some pitfalls of noise and trap measurements, addresses them adequately, and demonstrates their limitations. Noise-spectrum measurements should be conducted in a specific range limited by the shot-noise current and the gain bandwidth. In addition, the shallow and slight trap-density reduction can be captured by capacitance-voltage and capacitance-frequency measurements using a series resistance correction. The adequate measurement settings play a vital role in extracting the key physical characteristics of the recent high-performance OPD.