Organic Field Effect Transistor (OFET) Materials

Since the organic field effect transistor (OFET) was firstly reported in 1986, related researches have been developed rapidly and made great breakthroughs. With the advantages of wide material source, compatible with flexible substrate, low temperature processing, organic field effect transistors (OFET) have been applied in many fields. Organic field effect transistor (OFET) materials need to meet some requirements. First, the LUMO or HOMO of a single molecule is favorable for electron or hole injection. Second, the solid crystal structure should provide sufficient molecular orbital overlap to ensure that there are no excessive energy barriers when the charge moves between adjacent molecules. Third, the size range of the single crystal should be continuously across the contact point of source and drain poles, and the orientation of the single crystal should make the direction of high mobility parallel to the direction of current.

Applications:

• Display field: The organic field effect transistor (OFET) has the advantages of high speed, high energy amplification and stable performance, which can be used as drivers in the display field. Organic field effect transistor (OFET) has been successfully used in polymer distributed liquid crystal displays, electronic ink displays, organic light-emitting diodes and others.

Figure 1. An example of organic field effect transistor (OFET) applied in display field.

• Sensor field: Organic field effect transistor (OFET) can be prepared as a gas sensor, and its core component is organic semiconductor. Organic semiconductors react directly with gas molecules with high selectivity, and the gas is analyzed qualitatively and quantitatively by changing transistor current-voltage characteristic parameters. In addition, organic field effect transistor can also be used as sensors for ion detection and biological detection.

Figure 2. An example of organic field effect transistor (OFET) applied as a sensor.

• The others: Organic field effect transistor (OFET) has many other applications, such as large-scale integrated circuits, organic lasers, and superconducting material preparation.

Classification:

Depending on the carrier, organic field effect transistor (OFET) materials can be divided into p-channel organic semiconductor material and n-channel organic semiconductor material.

• P-channel organic semiconductor material: According to the molecular weight, p-channel organic semiconductor materials can be classified into polymers, oligomers and organic small molecules. As for polymer, the film formation of polymer by solution method has good continuity, but the solubility and order are poor, and the field effect mobility is low. With regard to oligomers, the molecular orbital energy levels can be adjusted by flexibly changing the length of molecular chains and introducing functional groups to control and improve the transport of carriers. The typical representative materials are thiophene and its derivatives. Furthermore, compared with polymers, small organic molecules are easy to be purified, which can reduce the damage of impurity to crystal integrity and facilitate the carrier migration speed.

Figure 3. Typical molecular structure of p-channel organic semiconductor materials.

• N-channel organic semiconductor material: Most n-channel organic semiconductor compounds are sensitive to oxygen and humidity, and organic anions react easily with oxygen, resulting in low field effect mobility and unstable transistor performance. According to the molecular weight, n-channel organic semiconductor material also can be divided into polymers, oligomers and organic small molecules. Among them, organic small molecules are the most widely studied.

Figure 4. Typical molecular structure of n-channel organic semiconductor materials.

Reference:

1. Kim, Zin-Sig, Chul. Biotin-Functionalized Semiconducting Polymer in an Organic Field Effect Transistor and Application as a Biosensor.[J]. Sensors, 2012.