Far-infrared transparent conductive material

Transparent conductive materials are widely used in flat panel displays, solar cells, and emerging flexible transparent electronic products. At present, people have developed transparent conductive materials in the visible light, near infrared and mid-infrared bands, but the transparent conductive materials in the far infrared band have not been successfully developed, which limits the development of far-infrared electromagnetic shielding, infrared thermal camouflage, light detection, biological sensing and other technical fields.

High far-infrared transparency requires materials with extremely low light absorption in the 8-12 μm band. High conductivity requires materials with high carrier concentration and mobility. However, since carriers inevitably cause in-band transition absorption while transporting current, there is a certain conflict between high far-infrared transparency and high conductivity, which is a classic problem that limits the development of far-infrared transparent conductive materials.

Recently, the teams of Professor Zhu Jiaqi of Harbin Institute of Technology, Professor Hu Chaoquan and Professor Shen Liang of Jilin University have made breakthroughs in the field of far-infrared transparent conductive materials.

For the first time, they proposed a new strategy to achieve far-infrared transparent conductive synergy by increasing the optical permittivity, thus developing a family of far-infrared transparent conductive materials characterized by less electrons and multi-center bonds.

The results were published in Light: Science & Applications under the title “Far-infrared transparent conductors.” The corresponding authors of the paper are Professor Zhu Jiaqi of Harbin Institute of Technology, Professor Hu Chaoquan and Professor Shen Liang of Jilin University. The first author is Professor Hu Chaoquan of Jilin University, and the second author is Zhou Zijian, a master’s graduate of Jilin University. This work is especially grateful for the funding of the National Natural Science Foundation of China Key Project (52032004).

Figure 1 shows the R&D strategy and new materials for this paper.

First, the team discovered a special bond, a few-electron multi-center bond, which differs from traditional chemical bonds, and materials composed of such bonding have a great optical permittivity (εopt) due to their strong electron shift polarization effect (Figure 1a).

The team then found that low ionization, low hybridization, and low saturation were necessary for the formation of low-electron multicenter bonds, and based on this, they predicted that heavy metal chalcogenides in octahedral configurations and their solid solutions were a class of high-εopt materials (Figure 1b).

Through the verification experiments of four material systems, it is proved that the high-εopt material containing shallow energy level defects does have excellent far-infrared transparent conductive properties, filling the gap of far-infrared transparent conductive materials (Figure 1c).

Finally, the team used these high-εopt materials to develop the first “continuous film” type far-infrared electromagnetic shield, which outperformed conventional shielders (Figure 1d).

The new material can also be applied to other technical fields, such as far-infrared photodetectors (Figure 1e).

Figure 1: Far-infrared transparent and conductive material design. (a) Positive correlation between plasma absorption edge and optical permittivity. (b) Three formation conditions for less electrons and more central bonds, and the octahedral configuration of heavy metal chalcogenides and their solid solutions designed by the research team. (c) Plasma absorption edge and room temperature conductivity of traditional transparent conductive materials as well as newly developed materials. (d) “Continuous film” type far-infrared electromagnetic shield. (e) Far-infrared photodetectors.

Compared with the well-known visible light transparent conductive material ITO, the transparent conductive material in the far infrared band developed by the team is expected to play a role in photodetectors, invisible sensors and other fields, filling the technical gap that traditional ITO cannot touch. The solution to the bottleneck problem that infrared transparency and conductivity are difficult to coordinate will pave the way for the development of infrared photoelectronic physics, materials and devices. (Source: China Optics WeChat public account)

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