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Organic Field Effect Transistor (OFET) Materials
Introduction
Organic field-effect transistor (OFET) is one of field-effect transistor which uses organic semiconductor to compose carrier transmission, and plays an important role in the rectifier, amplifier and so on. It is a typical three-terminal structure (figure 1), in which three sections are source/drain power supply and gate, There is a dielectric layer and an organic semiconductor layer respectively between the electrodes. The dielectric layer is usually made of silicon dioxide or other insulating polymers, while the gate is usually made of metal or conductive polymers.
Fig. 1 The structure of OFET
When OFET works, the gate electrode will apply a voltage, and the charge will be induced between the semiconductor layer and the insulation layer, forming a conductive channel. Meanwhile, the carriers in the channel will be injected from the source electrode and migrate from the source electrode to the leakage electrode under the action of the electric field, thus forming a current.
According to the transport properties of carriers, it can be divided into three categories:
- One is a hole-dominated carrier device, that is, p-type OFET
- One is the electronic as the majority carrier of the device, that is, n-type OFET
- Another OFET device in which the number of holes and electrons is of the same order of magnitude or similar is bipolar OFET.
Materials
Based on the above three types of FET, they can be divided into small molecule semiconductor and polymer semiconductor according to the distinguish of organic layer. The commonly used organic semiconductor materials are as follows (Table 1)
Table 1 Materials used for different types of OFET[1-2]
| semiconductor | organic | Materials | |
| p-type | small molecule | Rhofluorene, Benzene and their derivatives | |
| polymer | Polythiophene, Pyrrole diketones and their derivatives | ||
| n-type | small molecule | Fullerene, Naphthalene carbodiimide | |
| polymer | Aromatic imides, Oligomers thiophene and derivatives | ||
Applications
OFET can be used in many fields such as flat panel display, sensor and radio frequency identification, and its application in sensor field is especially extensive. Therefore, the application of OFET in different types of sensors is mainly introduced below.
With the continuous exploration of physical parameter sensing, the application of OFET sensors is constantly expanding, and it can be divided into the following categories according to different principles:
- Gas sensor. Based on the ability of redox gas to lose and gain electrons, it is easy to compete for interface charge when contacting with materials, thus causing voltage changes of OFET devices, so as to detect different gas.
- Pressure sensor: The main strategy to construct OFET pressure sensor is to integrate OFET and pressure sensitive element, and give full play to the signal amplification function of transistor.
- Optical sensor: The use of photosensitive semiconductor materials, multi-component integration and the introduction of photosensitive interface modification layer can be effective methods to construct OFET optical sensor.
- Other sensors: In addition to pressure and light detection, magnetic field, temperature and other physical parameters also have a wide range of application prospects.
References
- H. Li, W. Shi, J. Song, et al. Chemical and biomolecule sensing with organic field-effect transistors[J]. Chemical Reviews, 2019, 119(1): 3-35.
- A. N. Sokolov, B. C. Tee, C. J. Bettinger, et al. Chemical and engineering approaches to enable organic field-effect transistors for electronic skin applications[J]. Accounts of Chemical Research, 2011, 45(3): 361-371.
