An Organic Electrochemical Transistor Integrated Photodetector for High Quality Photoplethysmogram Signal Acquisition

Abstract
The organic photodiode (OPD) is a promising building block for solution-processable, flexible, lightweight, and miniaturized photodetectors, ideal for wearable applications. Despite the advances in materials used in OPDs, their photocurrent and light responsivity are limited, and alternative methods are required to boost the signal response. Herein, a miniaturized organic electrochemical transistor (OECT) is integrated with an OPD module to unlock the potential of OPDs to acquire physiological signals. In this integrated photodetector (IPD) system, the light intensity regulates the OPD voltage output that modulates the OECT channel current. The high transconductance of the OECT provides efficient voltage-to-current conversion, enhancing the signal-to-noise ratio on the sensing site. A microscale, p-type enhancement-mode OECT with high gm and fast switching speed performs better in this application than depletion-mode OECT of the same geometry. The IPD achieves a photocurrent and responsivity 318 and 140 times higher than the standalone OPD, respectively. It is shown that with the IPD, the amplitude of the photoplethysmogram signals detected by the OPD is enhanced by a factor of 2.9 × 103, highlighting its potential as a wearable biosensor and to detect weak, often uncaptured, light-based signals from living systems.

Citation
Zhong, Y., Koklu, A., Villalva, D. R., Zhang, Y., Hernandez, L. H., Moser, M., Hallani, R. K., McCulloch, I., Baran, D., & Inal, S. (2022). An Organic Electrochemical Transistor Integrated Photodetector for High Quality Photoplethysmogram Signal Acquisition. Advanced Functional Materials, 2211479. Portico. https://doi.org/10.1002/adfm.202211479

Acknowledgements
The authors acknowledge Hu Chen for pgBTTT preparation. This publication was based upon work supported by KAUST under Award Nos CCF/1976-33-01, REI/1/5130-01, ORA-2021-CRG10-4650 and -4668.

Publisher
Wiley

Journal
Advanced Functional Materials

DOI
10.1002/adfm.202211479

Additional Links
https://onlinelibrary.wiley.com/doi/10.1002/adfm.202211479

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