n-Type Organic Semiconductors
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Introduction
N-type semiconductor materials are to point to materials that regard electrons as carriers for transport in the ion domain band. To improve the stability and mobility of n-type organic semiconductor materials, the lowest unoccupied molecular orbitals (LUMO) energy level can usually be lowered by adjusting the electron affinity, such as the introduction of strong electron-absorbing groups -CN, -NO, or -F, etc., which makes the injection and transport of electrons possible, which is the main way to obtain efficient N-channel semiconductor materials or adding a passivation layer on its surface or completely wrapping the package to achieve. Since n-type semiconductor materials are less and less stable than required, but it is an important part of the bipolar transistor, so the development of stable and high-performance n-type organic semiconductor materials is of great importance. There are several materials that are detailed.
- Siloles
Siloles (silacyclopentadienes, Fig. 1) have recently attracted attention as semiconductor materials for organic electronics since they may exhibit high electron mobilities and high photoluminescence quantum yields. Silicon is a relative electropositive atom and therefore is inductively electron donating with the bonding σ -framework. However, through mixing of the π∗orbital of the diene with relatively low-lying set of σ∗ orbitals of the out of plane substitutents on the silicon atom, an orbital that has π∗–σ∗ conjugation can be created. Through this π∗–σ∗conjugation, the LUMO is somewhat lowered in energy and consequently the molecules can be reduced at potentials accessible for some organic electronic applications, in particular in OLEDs and allowing them to be used as electron transport materials.
Fig. 1 Chemical structure of bipyridine-substituted silole (a) and 1,1-bis(pentafl uorophenyl)-2,3,4,5-tetraphenylsiloles(b).
- Rylene diimides
Rylene diimides can exhibit relatively high electron affinities, high electron mobilities, and excellent chemical, thermal, and photochemical stabilities. These materials are electron deficient due to the substitution of an aromatic core with two sets of π-accepting imides groups that are mutually conjugated. Rylene diimide derivatives have been used not only as building blocks for electronic devices such as OLEDs, dye lasers, optical switches, and photodetectors,but also as electron acceptors in conjunction with electron donors for studying photoinduced energy- and electron-transfer processes. The widely used rylene diimides include both polymers and small molecules, and some specific chemical structures are shown in the fig. 2 and fig. 3.
Fig. 2 Chemical structure of some rylene diimide small molecules.
Fig. 3 Chemical structure of some rylene diimide polymers
Application
N-type organic semiconductor materials for organic electronic applications have a variety of design requirements that are application specific. Thus, it can be used in devices such as organic light emitting diodes (OLEDs), organic photovoltaics (OPVs) and organic field effect transistors (OFETs) depending on their different characteristics. Not only will the optimal material itself be application specific, but in many (most) cases the choice of material will be system specific, i.e., the organic semiconductor will be working in a system of materials and it will be necessary to match various materials parameters of the n-type material according to its ability to interact and function properly with the other materials in the system.
References
- ANTHONY, John E., et al. n-Type organic semiconductors in organic electronics. Advanced Materials, 2010, 22.34: 3876-3892.
- OKAMOTO, Toshihiro, et al. Robust, high-performance n-type organic semiconductors. Science advances, 2020, 6.18: eaaz0632.