Ultraflexible near-infrared organic photodetectors for conformal photoplethysmogram sensors

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

Research output: Contribution to journalArticlepeer-review

162 Citations (Scopus)


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 polyin-dacenodithiophene-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.

Original languageEnglish
Article number1802359
JournalAdvanced Materials
Issue number34
Publication statusPublished - 2018 Aug
Externally publishedYes


  • Flexible photodetectors
  • Mechanical conformability
  • Near infrared photodetectors
  • Regioregular polymers
  • Ultrathin photonic devices

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering


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