While photothermoelectric (PTE) sensor sheets are potentially suitable for testing applications, such as nondestructive material identifications in ultrabroad millimeter-wave infrared bands, their device designs have primarily employed a single-material channel. Herein, PTE sensor sheets generally combine photoinduced heating with associated thermoelectric (TE) conversion phenomena, and the employment of a single-material channel regulates device operations by missing opportunities for fully utilizing their fundamental parameters.

For this situation, this work develops all-solution-processable and freely coatable (paintable) hybrid PTE sensors by an effective combination of the channel structure with bismuth composite (Bicom) TE electrodes (Seebeck coefficient > 100 μV K−1) and efficient carbon nanotube film photothermal absorbers. This hybrid PTE sensor device stably forms its TE electrodes as easy-to-handle pastes of Bicom material powders with high Seebeck coefficients by effectively employing conductive solvents and surfactants.

Following these material and process preparations, the hybrid PTE sensor functions in ultrabroadband regions beyond the conventional detectors with comparable sensitivities to the existing narrowband devices in individual ranges and provides diverse optical measurement opportunities. Indeed, the easy-to-handle device fabrication process and advantageous photodetection performances of the hybrid PTE sensor demonstrate high usability for nondestructive testing applications (noncontact inspections, panoramic 3D camera monitoring, and portable device setups).

Introduction

In recent automation trends for social manufacturing and distribution sectors, nondestructive testing techniques play an indispensable role.[1, 2] The major expected inspection targets are internal material identifications for 3D objects. This situation is mainly because most commodities and industrial products are composed of combining various 3D spatial positions and shapes of composite materials.[3, 4] For the above situation, the use of longer-wavelength photosensor sheets is effective as inspection devices.

In particular, the longer-wavelength photosensor sheets potentially identify internal materials of various 3D objects regardless of shape and size configurations in a nondestructive manner. Here, the inherent optical properties of longer-wavelength photoirradiation, such as millimeter-wave (MMW),[5] terahertz (THz),[6] and infrared (IR),[7] provide the above potentials. In general, MMW–IR irradiation exhibits noninvasive permeability to various nonmetallic materials.[8, 9] Furthermore, transmittance values of nonmetallic materials to MMW–IR irradiation are specifically variable depending on compositions and wavelengths.[10, 11] In other words, MMW–IR irradiation nondestructively identifies core constituent materials (e.g., glass, semiconductor, plastic, ceramic, and so on) of commodities and industrial products.

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