Ultraflexible Near‐Infrared Organic Photodetectors for Conformal Photoplethysmogram Sensors

• Published in: Advanced materials (Weinheim) Vol. 30; no. 34; pp. e1802359 - n/a
• Main Authors: Park, Sungjun, Fukuda, Kenjiro, Wang, Ming, Lee, Chulhyo, Yokota, Tomoyuki, Jin, Hanbit, Jinno, Hiroaki, Kimura, Hiroki, Zalar, Peter, Matsuhisa, Naoji, Umezu, Shinjiro, Bazan, Guillermo C., Someya, Takao
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.08.2018
• Subjects: Bend radius; Deformation; flexible photodetectors; Heterojunctions; Materials science; mechanical conformability; near infrared photodetectors; Optoelectronic devices; Photometers; regioregular polymers; Sensors; ultrathin photonic devices; mechanical conformability; flexible photodetectors; regioregular polymers; near infrared photodetectors; ultrathin photonic devices
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201802359

Flexible organic optoelectronic devices simultaneously targeting mechanical conformability and fast responsivity in the near‐infrared (IR) region are a prerequisite to expand the capabilities of practical optical science and engineering for on‐skin optoelectronic applications. Here, an ultraflexible near‐IR responsive skin‐conformal photoplethysmogram sensor based on a bulk heterojunction photovoltaic active layer containing regioregular polyindacenodithiophene‐pyridyl[2,1,3]thiadiazole‐cyclopentadithiophene (PIPCP) is reported. The ultrathin (3 µm thick) photodetector exhibits unprecedented operational stability under severe mechanical deformation at a bending radius of less than 3 µm, even after more than 103 bending cycles. Deliberate optimization of the physical dimensions of the active layer used in the device enables precise on/off switching and high device yield simultaneously. The response frequency over 1 kHz under mechanically deformed conditions facilitates conformal electronic sensors at the machine/human interface. Finally, a mechanically stretchable, flexible, and skin‐conformal photoplethysmogram (PPG) device with higher sensitivity than those of rigid devices is demonstrated, through conformal adherence to the flexuous surface of a fingerprint. An ultraflexible near‐infrared (IR) organic photodetector that simultaneously exhibits both high speed (response frequency > 1 kHz at −3 dB) and small bending radius (r = 3 μm) is developed. Stable charge carrier transport is exhibited when the device is attached to a curved and/or folded part of the human skin, enabling a fingerprint conformal photoplethysmogram sensor.