Infrared Organic Photodetectors Employing Ultralow Bandgap Polymer and Non-Fullerene Acceptors for Biometric Monitoring

Recent efforts in the field of organic photodetectors (OPD) have been focused on extending broadband detection into the near-infrared (NIR) region. Here, two blends of an ultralow bandgap push-pull polymer TQ-T combined with state-of-the-art non-fullerene acceptors, IEICO-4F and Y6, are compared to obtain OPDs for sensing in the NIR beyond 1100 nm, which is the cut off for benchmark Si photodiodes. It is observed that the TQ-T:IEICO-4F device has a superior IR responsivity (0.03 AW(-1) at 1200 nm and -2 V bias) and can detect infrared light up to 1800 nm, while the TQ-T:Y6 blend shows a lower responsivity of 0.01 AW(-1). Device physics analyses are tied with spectroscopic and morphological studies to link the superior performance of TQ-T:IEICO-4F OPD to its faster charge separation as well as more favorable donor-acceptor domains mixing. In the polymer blend with Y6, the formation of large agglomerates that exceed the exciton diffusion length, which leads to high charge recombination, is observed. An application of these devices as biometric sensors for real-time heart rate monitoring via photoplethysmography, utilizing infrared light, is demonstrated.

Automated summary

Recent research in organic photodetectors (OPD) has focused on extending broadband detection into the near-infrared (NIR) region. In this study, two blends of a low bandgap polymer, TQ-T, with non-fullerene acceptors, IEICO-4F and Y6, were compared for their ability to sense NIR light beyond 1100 nm. The TQ-T:IEICO-4F device showed superior infrared responsivity and could detect light up to 1800 nm, while the TQ-T:Y6 blend had lower responsivity. Device physics analysis and spectroscopic studies revealed that the superior performance of TQ-T:IEICO-4F OPD was due to faster charge separation and improved donor-acceptor domain mixing.