Highly Sensitive Photodetectors For Medical Sensor

By Jay Soni

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New green-light absorbing photodetectors could be useful for medical sensors, fingerprint recognition, and more.

Researchers have developed a highly sensitive transparent organic photodetector that absorbs green light. This photodetector is compatible with CMOS fabrication methods. Using these photodetectors in organic silicon hybrid image sensors can have a variety of applications like light-based heart-rate monitoring, fingerprint recognition, and devices that detect the presence of nearby objects.

Transparent Organic Photodetector. | Credit: Sungjun Park, Ajou University

“For organic photodetectors to be incorporated into mass-produced CMOS image sensors requires organic light absorbers that are easy to fabricate on large scales and can accomplish vivid image recognition and produce distinct images in the dark with a high frame rate,” said Sungjun Park from Ajou University in the Republic of Korea, who co-led the research team. “We developed transparent green-sensitive organic photodiodes that can meet these requirements.”

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“The green-selective light-absorbing organic layer used in these image sensors considerably reduced crosstalk between the different colored pixels thanks to the introduction of a mixed organic buffer layer,” said research team co-leader Kyung-Bae Park from the Samsung Advanced Institute of Technology (SAIT) in the Republic of Korea.

Most organic materials are temperature sensitive and hence are not suitable for mass production. In order to overcome this problem, researchers focused on modifying the photodetector’s buffer layer to improve stability, efficiency, and detectivity.

“We introduced a bathocuproine (BCP):C60 mixed buffer layer as an electron transporting layer,” said Sungjun Park. “This gave the organic photodetectors exceptional characteristics, including higher efficiency and an extremely low dark current, which reduces noise.” This photodetector can be placed on a silicon photodiode with red and blue filters to create a hybrid image sensor.

The detectors were recorded to operate stably under temperatures above 150 °C (302 °F) for 2 hours and showed long-term operational stability at 85 °C (185 °F) for 30 days. This photodetector could allow high-performance organic photodiodes to become the main component for imaging modules and optoelectronic sensors used in a variety of applications.


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