Siloles For Semiconductors

Silole is a compound formed by replacing the bridgehead carbon atoms in cyclopentadiene with silicon atoms. In the silole structure, the σ bond of the outer ring of the silicon atom and the π bond of the cyclopentadiene form a σ-π conjugation, so that the lowest unoccupied orbital (LUMO) energy of the silole molecule is much lower than five-membered ring structures such as of pyrrole, furan, thiophene and pyrimidine. This property of silole makes it have strong electron affinity and high electron mobility, which plays an important role in the field of optoelectronic materials. For the functionalization of silole, the main purpose is to tune the electronic structure and luminescence properties of silole. The electronic structure of silole is largely affected by the substituents on the silole ring, especially the structural modification at positions 2 and 5 has the greatest impact on the LUMO energy level. In addition, the silicon atom of the silole unit adopts sp³ hybridization, and the introduction of two flexible chain substituents on the silicon atom can improve the solubility of the compound. In siloles small molecule semiconductor materials, in addition to directly modifying the simplest silole ring, structures such as silicon-bridged π-conjugated fused rings, bisilole thiophene, and spiro silole can also be formed. The unique electronic structures of silole derivatives makes them have excellent performance and unique photophysical properties, and are widely used in the fields of solar cells and organic optoelectronic materials.

Figure 1. Simple chemical structures of silole

Electroluminescent material: In organic electroluminescent devices (OLEDs), siloles small molecule semiconductor materials can be used as both electron transport materials and light emitting materials. As an electron transport material, the low LUMO energy level of siloles organic small molecules makes it have good electron transport properties. Therefore, OLEDs with silole derivatives site transport materials have excellent photoelectric conversion efficiency. As light-emitting materials, silole derivatives generally have stable blue light emission with high color purity. Through chemical modification, the silole derivatives also have a unique aggregation-induced fluorescence behavior, and the fluorescence is sharply enhanced in the aggregation state. The application of such materials improves the thermal stability and quantum efficiency of OLEDs and prolongs the service life of OLEDs.
Photovoltaic devices: The high electron affinity of siloles enables it to be used as an electron acceptor to prepare D-A (donor-acceptor) transport materials for photovoltaic applications. Such materials can stably migrate the holes and electrons separated from the respective donor and acceptor regions to the corresponding electrodes along the fake surface, complete the photovoltaic process from light to electricity, and improve the photoelectric conversion efficiency of the device.

Reference

Yuanjing Cai, Anjun Qin, Ben Zhong Tang. Siloles in optoelectronic devices [J]. J. Mater. Chem. C, 2017, 5, 7375-7389.

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