A high-sensitivity near-infrared phototransistor based on an organic bulk heterojunction

Haihua Xu, Jun Li, Billy H.K. Leung, Carmen C.Y. Poon, Beng ONG, Yuanting Zhang, Ni Zhao*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

135 Citations (Scopus)


High-gain photodetectors with near-infrared (NIR) sensitivity are critical for biomedical applications such as photoplethysmography and optical coherence tomography where detected optical signals are relatively weak. Current photodetection technologies rely on avalanche photodiodes and photomultipliers to achieve high sensitivity. These devices, however, require a high operation voltage and are not compatible with CMOS based read-out circuits (ROCs). In this work we demonstrate a solution-proceeded NIR phototransistor structure based on a bulk heterojunction (BHJ) of a narrow bandgap polymer, poly(N-alkyl diketopyrrolo-pyrrole dithienylthieno[3,2-b]thiophene) (DPP-DTT), and [6,6]-phenyl-C61-butyric acid methylester (PCBM). The device exhibits ultrahigh responsivity (∼5 × 105 A W-1) as well as wide tunability (>1 × 104) of photoconductive gain. Using the current-voltage and transient photocurrent measurements we show that the high responsivity is due to the combined effects of fast transport of holes in the polymer matrix and slow detrapping of electrons from the isolated PCBM domains. The wide gain tunability and the efficient suppression of noise current are achieved through the use of the optically tunable gate terminal. We demonstrate that our phototransistor can be used as the detection unit in a photoplethysmography sensor for non-invasive, continuous finger pulse wave monitoring. The high-sensitivity of the phototransistor allows the use of a low-power light source, thus reducing the overall power consumption of the sensor. This, together with the solution processibility and the simple device configuration (which is compatible with conventional ROCs), make the phototransistor a very promising component for the next generation low-cost, mobile biomedical devices for health monitoring and remote diagnostics.

Original languageEnglish
Pages (from-to)11850-11855
Number of pages6
Issue number23
Publication statusPublished - 7 Dec 2013

Scopus Subject Areas

  • Materials Science(all)


Dive into the research topics of 'A high-sensitivity near-infrared phototransistor based on an organic bulk heterojunction'. Together they form a unique fingerprint.

Cite this