Organic photodetectors (OPDs) have received significant attention in recent years due to their high extinction coefficients, lightweight, low-cost, and mechanical flexibility. Compared to conventional broadband photodetectors, narrow-band photodetectors offer high selectivity, low noise, and superior sensitivity. However, traditional narrow-band organic photodetectors often require high bias voltages to achieve self-filtering functionality, resulting in higher power consumption and limiting their practical applications.

To address these challenges, the research team led by Distinguished Professor Fang-Chen Chen from the Department of Photonics at National Yang Ming Chiao Tung University has introduced an innovative concept called photomultiplication narrowing (PMN). By employing a pseudo-bilayer structure, the new device enables highly efficient self-filtering functionality and exhibits high device sensitivity for deep red light. It achieves exceptional external quantum efficiency (EQE) and superior photodetection performance under low bias conditions.

Because narrow-band OPDs require effective self-filtering capabilities, the active layer must be sufficiently thick to absorb or filter out unwanted light sources. Consequently, driving narrow-band OPDs typically necessitate higher biases. The PMN mechanism addresses this challenge by employing a pseudo-bilayer structure that integrates two distinct functionalities: a photon-filtering (PF) layer and a photomultiplication (PM) layer. As light passes through the PF layer, short-wavelength photons are fully absorbed. On the other hand, light with longer wavelengths near the band edge of the PF material is selectively transmitted into the PM layer, thereby triggering the PM effect. This tight synergy between the two layers enables the OPDs to exhibit a remarkable PM effect, achieving an EQE of up to nearly 6000%, meaning that approximately 60 electrons are generated for every photon. More importantly, this performance is achieved with just a 5V operating voltage. In comparison, traditional self-filtering OPDs typically require 50-60V to operate, representing a significant reduction in power requirements for the new generation PMN-based OPDs. The low-bias OPDs are much more energy-efficient for practical applications.

Deep red light sensing has numerous applications in fields such as biomedicine, bioimaging, and remote sensing. This groundbreaking research, published in the outstanding journal “Advanced Optical Materials”, opens a new avenue for the development of high-performance narrow-band OPDs. It not only achieves high sensitivity and fast response but also significantly enhances energy efficiency, offering a promising direction for future advancements in this technology.