The Innovation Factory has a patent portfolio available for technology which reduces the band gap of benzothiadiazole-based polymers via a synthetic route.
In this synthetic route, the band gap is reduced firstly by adding a boron group to the benzothiadiazole acceptor unit. The boron is then reacted with the adjacent polymer unit, creating a rigid structure that increases conjugation. After these two stages, bulky groups can be added to the boron groups to reduce reactivity with water.
Semiconductors can be described as the foundation of modern electronics and are present in many electronic devices such as transistors, solar cells and light-emitting diodes (LEDs). A semiconductor is a material that is able to conduct an electric current between a conductor and an insulator. Semiconducting polymers are made up of alternating acceptor and donor molecules, allowing electrons to travel via conjugation of alternating single and double bonds. The band gap of a semiconductor is a crucial feature. In semiconductors with a low band gap, the energy needed to excite an electron from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) is small. Low band gap semiconductors are more effective and are able to interact with light in the visible or near-infrared region of the spectrum.
Previous efforts have focused on reducing the band gap of semiconductors. It has been reported that the band gap can be reduced by bonding a boron species to the nitrogen of benzothiadiazole acceptor units. The boron is able to accept an electron pair from the nitrogen, lowering the LUMO, and decreasing the band gap. This does however carry limitations, as the boron centre can be unstable and react easily with water. Bulky groups can be used to block reactions with the boron, however this can be unsuccessful. The band gap has also been shown to decrease when the polymer background is fused between the donor and acceptor. This increases conjugation and enhances electrical communication between the donor and acceptor units. Until now, there have been no reports of using these methods simultaneously.
- Reduces the band gap of benzothiadiazole-based polymers.
- Bridges the band gap into the visible/ near infra-red region- allowing interaction with light in this region.
- Boron groups can be modified to increase stability with water.
- Semiconducting polymers are cheaper and easier to process in comparison with silicon-based semiconductors.
- Photovoltaic devices- a small band gap would allow light to excite electrons in order to generate an electric current. Benzothiadiazole-based polymers modified by this technology could be used to harvest light from the optical region.
- Photosensitiser in dye-sensitised solar cells – the small band gap in the optical region could allow light to be harvested.
- Organic light emitting diodes- this technology could be used for LEDs with low band gaps, for example blue light LEDs. Efficient and cost-effective inorganic light emitting diodes of this type are difficult to create.
- Organic field effect transistors- this technology would create a rigid and orderly packed conducting polymer which would enhance movement of electrons along the structure.
- Conductive ink/printer electronics- the small band gap of modified polymers could allow higher conductivity at lower applied voltages. This would increase power efficiency.
- Flexible/wearable electronics.
- Antistatic coatings.
To acquire the full patent portfolio for the technology (‘20130234’).
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