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  • Semiconductor Blocks

    Semiconductor Blocks is an organic electronic material that is composed of polymer compounds and has semiconductor properties and can be used to make semiconductor devices and integrated circuits. The electrical conductivity is in the range of 10-10~102 S/cm, and the bandgap width of polymer semiconductors is similar to that of inorganic semiconductors. Its conductivity comes from the π electrons of conjugated bonds, including highly conjugated polymers and charge transfer polymers doped with iodine or alkali metals. Conjugated polymers mainly include polybenzene, polyacetylene, polyvinyl carbazole, polyphenylene sulfide and so on. Charge transfer composite polymers such as polyvinyl carbazole-trinitrofluorenone, etc. can be used in black-and-white electrostatic copier, color laser copier and laser printer.

    Applications:

    • Optoelectronic devices: Semiconductor polymer with photoelectric conversion function is a promising conjugated polymer material that is expected to replace inorganic materials in the field of photoelectric conversion. It can be used to make large-area, low-cost photodetectors and solar cells. Among the semiconductor polymer materials with optoelectronic activity, polyvinyl carbazole (PVK) is the earliest discovered and fully studied. There is a large electron conjugation system on the side group of PVK, which can absorb ultraviolet light, and the excited electrons can migrate freely through the adjacent carbazole ring to form a charge-transfer complex. Another kind of conjugated polymer semiconductor materials that have attracted much attention is poly (p-phenylene ethylene) and its derivatives.

    The structural formula of polyvinyl carbazole. Figure 1. The structural formula of polyvinyl carbazole.

    • Gas sensor: Semiconductor polymers also have a good application prospect in the preparation of room temperature gas sensors. The conductivity of organic semiconductor polymer will change when it interacts with the oxidant or reducing agent. Generally speaking, most organic semiconductor polymers are p-type semiconductors and belong to the π-conjugated structure. When gas molecules interact with conductive polymers, they can be used as electron donors or electron acceptors, which will lead to the increase or decrease of carrier concentration in conductive polymers, resulting in changes in the electrical conductivity of conductive polymer materials. Among them, polyaniline (PANI) is a widely studied conductive polymer material, which has the advantages of high sensitivity, strong selectivity and fast response.

    The polymer-based flexible gas sensor Figure 2. The polymer-based flexible gas sensor

    • Photocatalyst: Some researchers have found that non-metallic polymer graphite phase carbon nitride (g-C3N4) can complete hydrogen evolution and oxygen production respectively in the presence of visible light and different sacrificial agents, which has aroused a great deal of attention in the study of carbon nitride and its derivative polymers instead of metal oxides as photocatalysts. g-C3N4 not only has the advantages of abundant sources and low price of general polymer semiconductors but also its excellent photocatalytic performance and stability make it comparable to traditional inorganic semiconductors.

    g-C<sub>3</sub>N<sub>4</sub>-Based Nanomaterials for Visible Light-Driven Photocatalysis Figure 3. g-C3N4-Based Nanomaterials for Visible Light-Driven Photocatalysis

    • Laser printer: The photosensitive body of the new photocopier has adopted a multi-layer structure with functional separation, which is composed of 0.1~1 μm thick carrier generating layer (CGL) and 10~30 μm thick carrier transport layer (CTL), which improves the light sensitivity of the photocopier. The CGL layer is made of ultra-fine organic photoconductive materials dispersed in polymers such as polyvinyl butyral. The organic photoconductive materials are phthalocyanines or azo compounds with a large number of π electrons. The CTL layer is composed of organic semiconductors with high mobility. Bulk materials are dispersed in polymers such as polycarbonates. Organic photosensors are rich in resources, pollution-free, simple film-forming process and low cost, so they play an important role in laser printers.

    References:

    1. Günes S, Neugebauer H, Sariciftci NS.(2007) “Conjugated polymer-based organic solar cells.” Chemical reviews. 107(4): 1324-38.
    2. Chen X, Liu Q, Wu Q, Du P, Zhu J, Dai S.(2016) “Incorporating Graphitic Carbon Nitride (g-C3N4) Quantum Dots into Bulk-Heterojunction Polymer Solar Cells Leads to Efficiency Enhancement.” Advanced Functional Materials. 26(11): 1719-28.

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