The application of semiconductor materials is very wide, and different application fields will use semiconductor materials with different properties. Organic semiconductor materials are generally designed based on small molecules, polymers, and donor-acceptor(D-A) molecular systems. Organic semiconductors in the D-A system have higher electron mobility due to easier electron migration. Donor molecules that can be used as organic semiconductor materials generally have the following characteristics: (1) It has a low ionization potential and is easy to donate electrons; (2) Intramolecular groups capable of pushing electrons, such as N, N-dimethylamino, alkyl, alkoxy, etc.; (3) has a large polarization ability. Organic donor molecules are easy to modify, and the properties of organic semiconductors can be adjusted by changing the molecular structure to expand the application fields of semiconductor materials.
Figure 1. OPV device structure and photoelectric conversion mechanism (TCO=transparent conductive oxide)
- Organic photovoltaic devices (OPV): OPV devices mainly use heterojunctions, including p-n heterojunctions, bulk heterojunction(BHJ) and cascade structures. This kind of material selects matching donor and acceptor materials to obtain broad absorption, which is higher than the photoelectric conversion efficiency of simple junction devices. The donor molecules in the OPV active layer bear the functions of absorbing light, generating excitons, and transmitting excitons and holes. The common ones are oligothiophenes, triphenylamines, pyrrolopyrrole diketones, benzodithiophenes and other heterocyclics. The modification of the donor molecule will affect the light absorption and exciton transmission of the OPV device, and improve the photoelectric conversion efficiency.
- Organic Light Emitting Diode (OLED): OLED is a semiconductor light emitting material that can cause light emission under the injection and recombination of carriers. The properties of semiconductor materials determine the luminous efficiency of OLEDs. The organic semiconductor materials of the D-A molecular system can produce ultra-thin, fast response, and high luminous efficiency OLED devices.
- Organic field effect transistor (OFET): OFET refers to devices made with organic semiconductors as active materials. Organic semiconductor materials with D-A system can prepare OFET devices with stable electrochemical characteristics. Common donor molecules with strong π-π interactions such as thiophene ring system and polycyclic aromatic hydrocarbons. Various structures and multi-position modifications can effectively modify semiconductor materials to obtain OFET devices with excellent performance.
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