Photovoltaic energy is commonly known to work within solar panel technology through the generation of power. Devices such as social cells are utilized, which absorb energy from the sun and subsequently convert it into electrical energy using semiconductive materials. The use of photovoltaic technology has provided a sustainable solution for a more renewable source of energy. However, introducing carbon nanotubes to this field could be revolutionary.
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This article provides an overview of research into carbon nanotube use within photovoltaics and how this may affect future directions of this sector within sustainable energy.
The Benefits of Carbon Nanotubes
Carbon nanotubes (CNTs) refer to cylindrical molecules comprised of rolled-up sheets of a single layer of graphene carbon atoms. These molecules can either be single-walled (SWCNT) with less than 1 nm in diameter or multi-walled (MWCNT), possessing several interlinked nanotubes reaching more than 100 nm in diameter. The chemical bonds between CNTs are extremely strong, making them a significant contender for use within novel materials.
With promising characteristics such as high strength and low weight, along with highly conductive and thermal properties, this nanotechnology has become popular for use within structural reinforcement. Their use extends to polymers, enhancing conductivity or as a method to control it, such as within anti-static packaging. CNTs are also used in bulk composite materials and thin films.
SWCNTs have shown great potential to be used for next-generation technology due to benefits like flexibility and the potential to be made entirely from carbon. As a result, sustainable disposal at the end of a product’s life cycle would be enabled, allowing the progression of green initiatives within companies.
While the applications of SWCNTs are varied, ranging across photonics, telecommunications, batteries, memory devices, and cancer research, there has been further research into its use within photovoltaic technology.
Carbon Nanotubes for Photovoltaic Technology
Carbon nanotubes can be used as a versatile material within photovoltaic technology, particularly throughout different components of solar cells, such as light-sensitive components and carrier-sensitive contacts. Applications also extend to replacing layers used for passivation, which renders metals inert through a thin coating on the surface.
Transparent conducting films can also be replaced by CNTs as they usually require materials that enable electrical conductivity. Furthermore, the optical transparency and versatility of CNTs evidence their suitability as an effective alternative.
The chemical stability and conductivity of CNTs, especially SWCNTs, increase their suitability for generating novel solar cells and light-sensitive elements. However, its use within the commercial solar market is complex, requiring further research before being a viable option.
Research into areas such as separation, purification, and enrichment of CNTs, as well as integration into photosensitive elements for use as organic solar cells or silicon solar cells as a hole-sensitive contact, would be beneficial for their introduction into the commercial industry. For this to occur, industrial discussions around cost would have to be influenced, which would cause significant changes to production lines.
It is still impossible for researchers to selectively create SWCNTs of an arbitrary chirality level that depends on asymmetry. After all, their atomic structure is determined by their chirality and ability to “roll up” their graphene lattice structure.
Research towards achieving chiral-specific growth is still being undertaken, including methods like metal-catalyst-free nanotubes cloning of single chirality seeds, and using bimetallic solid alloy catalysts.
The separation, purification, and enrichment of CNTs are necessary for photovoltaic applications. They are advanced processing procedures that ensure the yield and chirality of pure CNTs are of a more optimum level. However, the high cost of these pure CNTs, regardless of the separation method, is still disadvantageous for companies that may already benefit from the current low-cost alternatives.
The Future of CNTs in Photovoltaics
Moving CNT photovoltaics into industry requires further effort to upscale their purification.
Post-synthesis purification techniques may have progressed to the capability of sorting a 2:1 mixture of CNT soot according to diameter, length, and other variables, yet this process still suffers from limitations such as low yield and high expense. Although scaled production would likely offset high costs, it may not be as economical as traditional organic photovoltaic materials like polythiophenes.
While these research areas have seen developments in the last 20 years, with high-performance silicon-based cells almost comparable to industrial production lines, there are still significant steps to be taken before commercial use of CNTs in the solar market.
Challenges, including the limited device area of technology derived from SWCNTs, price, and yield, illustrate the need for further research in this field. If so, CNTs could be an effective alternative for sustainable energy, reducing global pollution and the need for non-renewable energy sources.
Working through current obstacles of CNTs within photovoltaics, improvements in areas like increased light absorption and novel material combinations could impact industrial practice for many sectors, paving the way for a more sustainable future.
Further Reading and References
Eatemadi, A., et al. (2014) Carbon nanotubes: properties, synthesis, purification, and medical applications. Nanoscale Research Letters, 9(1), p.393. Available at: https://doi.org/10.1186/1556-276X-9-393 [Accessed August 2021].
Shakouri, M., Ebadi, H. and Gorjian, S., (2020) Solar photovoltaic thermal (PVT) module technologies. Photovoltaic Solar Energy Conversion, pp.79-116. Available at: https://doi.org/10.1016/B978-0-12-819610-6.00004-1 [Accessed August 2021].
Wieland, L., Li, H., Rust, C., Chen, J. and Flavel, B., 2020. Carbon Nanotubes for Photovoltaics: From Lab to Industry. Advanced Energy Materials, 11(3), p.2002880. Available at: https://doi.org/10.1002/aenm.202002880 [Accessed August 2021].