Shining light on the underlying mechanisms in photomultiplication-type organic photodetectors

Conventional inorganic photodiodes can maximally convert one photon to one electron without gain. In contrast, silicon photomultiplier tubes generate more than one electron per incoming photon and increase signal and sensitivity.

Recently, photomultiplication-type organic photodetectors have emerged as a promising candidate for next generation photodetection. However, the underlying mechanisms at work in these organic photodetectors are unclear. Their structure differs significantly from that of inorganic devices, changing the process behind the photomultiplication effect.

Bai et al. characterized the working mechanisms of photomultiplication-type organic photodetectors using advanced transient characterization techniques. To understand how the photodetectors convert photons into electrons, the researchers monitored changes with time in device signals, like transient photocurrent, photovoltage, and capacitance.

“This is the first study on the working mechanism with the help of advanced transient characterization techniques, which is of great importance to the field,” said author Qianqian Lin. “We revealed the photomultiplication process is a slow process, which had not been reported before, and also highly dependent on the light intensity, active layer composition, and bias voltage.”

The team introduced two strategies to improve device performance: interfacial engineering and composition optimization. Their photodetector design minimizes dark current and increases sensitivity.

“We also report the first application of photomultiplication-type organic photodetectors for pulsed light detection — an interesting field to explore,” said Lin.

While the organic photodetectors have high responsivity and low dark current and noise, improving the linear dynamic range and the device stability under high bias voltage remain as challenges the authors hope to undertake.

Source: “Transient analysis of photomultiplication-type organic photodiodes,” by Songxue Bai, Ruiming Li, Huihuang Huang, Yiming Qi, Yalun Xu, Jiannan Song, Fang Yao, Oskar J. Sandberg, Paul Meredith, Ardalan Armin, and Qianqian Lin, Applied Physics Reviews (2022). The article can be accessed at https://doi.org/10.1063/5.0083361 .