Highly Sensitive, Mass Producible Organic Photodetectors for Medical Sensors, Fingerprint Recognition



Researchers created highly sensitive, transparent organic photodetectors that are compatible with CMOS fabrication techniques. These photodetectors absorb green light. They created an organic-silicon hybrid RGB imaging sensor by fusing one of these green organic photodetectors with a silicon photodiode that had red and blue filters. Credit goes to Ajou University's Sungjun Park.

New photodetectors that absorb green light may be beneficial for fingerprint recognition, medical sensors, and other applications.

Researchers have created and demonstrated brand-new, highly sensitive, transparent organic photodetectors that can be made using CMOS manufacturing techniques. These novel photodetectors could be incorporated into organic-silicon hybrid image sensors for a variety of uses. These include tools for fingerprint identification, heart-rate monitoring based on light, and detecting the presence of surrounding items.

The majority of today's imaging sensors are based on CMOS technology and inorganic photodetectors, which transform light impulses into electric signals and are utilized in both scientific cameras and smartphones. Although organic photodetectors are gaining attention due to their potential to increase sensitivity, for instance, it has so far proven challenging to construct high-performance organic photodetectors.

"Organic light absorbers that are simple to fabricate on large scales and can accomplish vivid image recognition and produce distinct images in the dark with a high frame rate are required for organic photodetectors to be incorporated into mass-produced CMOS image sensors," said Sungjun Park from Ajou University in the Republic of Korea, who co-led the research team. We created transparent, environmentally conscious organic photodiodes that can satisfy these demands.

Today, August 25, 2022, the researchers publish a description of the novel organic photodetectors in Optica, a high-impact academic publication from Optica Publishing Group. By combining the transparent, green-absorbing organic photodetector with a silicon photodiode that had red and blue filters, they were also able to build a hybrid RGB imaging sensor.

Thanks to the addition of a mixed organic buffer layer, the green-selective light-absorbing organic layer used in these image sensors significantly reduced crosstalk between the various colored pixels, according to Kyung-Bae Park, a member of the research team from the Samsung Advanced Institute of Technology (SAIT) in the Republic of Korea. High-performance organic photodiodes may soon serve as the primary component of image modules and optoelectronic sensors utilized in a wide range of applications thanks to this novel design.

The sensitivity of most organic compounds to temperature makes them unsuitable for mass production. They either become unstable when utilized for an extended period of time at moderate temperatures or they are unable to sustain the high temperatures required for post-processing. The researchers concentrated on changing the buffer layer of the photodetector to increase stability, effectiveness, and detectivity to overcome this obstacle. A sensor's detectivity refers to how well it can pick up weak signals.

Sungjun Park stated, "We introduced a bathocuproine (BCP):C60 mixed buffer layer as an electron carrying layer. This resulted in the organic photodetectors having unique qualities, such as greater efficiency and a very low dark current that lowers noise. To make a hybrid image sensor, this photodetector can be attached to a silicon photodiode with red and blue filters.

The researchers showed that the detectivity of the novel photodetectors was on par with that of traditional silicon photodiodes. The detectors demonstrated long-term operational stability at 85 °C (185 °F) for 30 days while operating steadily at temperatures exceeding 150 °C (302 °F) for 2 hours. Additionally, the photodetectors showed good color expression.

The new photodetectors and hybrid image sensors will then be modified for usage in a variety of applications, including wearable and mobile sensors (including CMOS image sensors), proximity sensors, and fingerprint-on-display gadgets.

Transparent Organic Photodiodes for High-Detectivity CMOS Image Sensors, Optica, August 25, 2022, S. Park, Y. Lim, C.-J. Heo, S. Yun, D.-S. Leem, S. Kim, B. Choi, and K.-B. Park

By OPTICA 

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