Ultraflexible Near‐Infrared Organic Photodetectors for Conformal Photoplethysmogram Sensors

• DOI: 10.1002/adma.201802359
• Publication Date: 2018-07-09T06:24:51Z
• Authors: Sungjun Park; Kenjiro Fukuda; Ming Wang; Chulhyo Lee; Tomoyuki Yokota; Hanbit Jin; Hiroaki Jinno; Hiroki Kimura; Peter Zalar; Naoji Matsuhisa; Shinjiro Umezu; Guillermo C. Bazan; Takao Someya
• Keywords: 02 engineering and technology; 0210 nano-technology

AbstractFlexible 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.