In a recent paper published in Small Science, a research group at Chuo University, Japan, led by Assistant Prof. Kou Li, developed an all-printable device fabrication strategy to overcome the technical constraints of multi-functional image sensor sheets for non-destructive inspections.
Graphical abstract. Image Credit: Chuo University
The device designs of photo-thermoelectric (PTE) sensors have mostly used a single material as the channel, even though these sensors may be appropriate for testing applications like non-destructive material identification in ultrabroad millimeter-wave (MMW)–infrared (IR) bands.
PTE sensors typically integrate photo-induced heating with related thermoelectric (TE) conversion. Using only one material channel limits device use by preventing the full utilization of its basic parameters.
Such critical circumstances are brought about by long-standing technical challenges in the field of PTE sensor design, where typical constituent materials show trends of the trade-off between photo-absorptance values (for heating) and the Seebeck coefficients (for TE conversion).
This study made the following important contributions to achieve this goal.
- Creating the PTE sensor structure using a highly efficient hybrid combination of carbon nanotube (CNT) film photo-thermal absorber channels and bismuth composite (Bicom) TE electrodes (Seebeck coefficient > 100 µV/K).
- Making the most of the aforementioned beneficial hybrid strategy, the sensor performs photo-detection operations with response intensities that are more than ten times greater than those of single-material PTE detectors (usually pn-junction CNT films), meeting the readable signal range criteria (> several millivolts) for the device coupling with portable circuit modules.
- By skillfully positioning Bicom powders with conductive solvents and surfactants as paste-like stable TE converting electrodes along the naturally ink-formed CNT film absorber, the hybrid PTE sensor can be designed into all-solution-processable fabrication configurations.
- Assuring optical stabilities against extreme environmental conditions (such as high temperatures and cyclic deformations) while achieving ultrabroad MMW–IR operations with the hybrid paste PTE device over conventional wideband detectors in comparable sensitivities (minimum noise equivalent power: 560 fWHz−1/2) to current narrowband sensors.
- Utilizing the advantages of the aforementioned optical features and paste-unique freely paintable device setups, the hybrid PTE sensor demonstrates functional non-destructive imaging inspections at high usability. For example, by creating an easy-to-handle panoramic bowl camera module, omnidirectional observations of a 3D target without a blind spot are demonstrated.
Journal Reference:
Matsuzaki, Y., et al. (2025) All-solution-processable hybrid photo-thermoelectric sensors with carbon nanotube absorbers and bismuth composite electrodes for non-destructive testing. Small Science. doi.org/10.1002/smsc.202400448