Quantum dots (QDs) are already revolutionising consumer technologies. From enabling real-time health tracking in smart watches, to boosting the performance of home security systems, these nanoscale light-sensitive particles provide astounding benefits for short-wave infrared light sensing and imaging.
However, as QD synthesis processes advance, this technology will also start benefitting the systems that we use to combat climate change.
The sustainability industry is a hotbed of innovation. Exciting new developments are emerging each year that help us gather one of the most important sustainability tools: renewable energy.
Solar energy is one of the most abundant resources we have. Every second, 173,000 terawatts of energy from the sun hits the Earth’s surface, which can be collected by solar panels to produce clean, renewable power. In 2020, the world harvested just 716.2 gigawatts of this, which equates to around 0.0004%.
For context, humanity currently consumes less than 24,000 terawatt hours of power each year. In the UK, around 8% of all energy consumed comes from solar power, and that’s from one of the leading players in the solar energy field.
The untapped potential here is huge.
There are a few reasons for this limited usage of solar power, among which are the cost and availability of panels, and the comparative recency of solar cell development. However, current solar cell technology is also hindered by inherent limitations to is efficiency – and this is where QDs can help.
Solar cell technology depends on the ability of devices to generate ‘excitons’ – a bound electron-hole pair. Traditional solar cells only generate one exciton per incoming photon. This has limited their maximum attainable efficiency at around 32-33%, which is known as the Shockley-Queisser limit.
QDs demonstrate far improved optoelectronic properties, lending them tremendous potential in the field of solar energy capture. QD solar cells use QDs as their photovoltaic material, replacing traditional materials like silicon or copper indium gallium selenide. This enables them to convert light that would otherwise be ‘wasted’ into current through light fusion, using a photo sensitiser and emitter to change photons of a lower energy than the solar cell’s bandgap.
In essence, this allows QD solar cells to generate multiple excitons per photon.
This process is possible because QDs have high photo-stability and tuneable band gaps, meaning by changing their size, they can respond to different wavelengths of light. Smaller QDs are more responsive to shorter wavelengths, with smaller QDs experiencing larger shifts towards the blue end of the light spectrum.
Using QDs significantly improves the amount of light that solar cells can use, potentially hitting an efficiency peak of 66%, and meaning that any solar panels installed using this technology are able to convert more light into energy. This will increase the amount of renewable energy on the grid, helping to cut carbon emissions and aiding us in transitioning to a greener way of living.
Although QD-based solar cells feature higher efficiency, they have been hindered by stability of the materials. This is due to defects occurring during the QD synthesis process, which restrict the resulting power conversion efficiency of any solar cell that materials are used in. The high cost and low throughput of QD development presents another barrier.
Quantum Science’s innovative synthesis process overcomes both these issues. By creating QDs in the form of stable colloidal inks, INFIQ® technology can be deposited in a single step instead of 14-16, removing the need for wasteful chemical processing and standardising production. This method is significantly faster and less labour intensive, allowing for production of QD materials at unprecedented scale.
There are some safety issues to bear in mind when considering QDs for solar cell applications. Most QDs contain heavy metals like lead, which limits their use due to the inherent toxicity of this material. Thankfully, Quantum Science is capable of manufacturing lead-free QDs with market-leading performance. These lead-free QDs can be tuned from absorption wavelengths from 800nm to 1,500nm, and are both safer to handle and better for the environment.
With solar cell technology struggling to push into the next generation of performance, QDs promise to overcome existing issues, and significantly increase our ability to turn sunlight into clean, renewable energy.