One of the most promising emerging solar cell technologies has seen a huge boost in efficiency. Engineers at UNIST in South Korea have created a quantum dot solar cell with a world record efficiency of 18.1%. Quantum dots are essentially just tiny, round semiconductor crystals that absorb and emit light with astonishing efficiency. By changing the size of quantum dots, you can set the color of the light that interacts with them, making them useful in display technology or sensors.
However, they may ultimately find their greatest use in solar cells. Most commercial solar cells use a bulk material as the light-collecting layer, meaning the entire surface absorbs the same wavelengths. But quantum dots can come in a variety of sizes, focusing on different parts of the spectrum, increasing potential efficiency. Additionally, quantum dots are cheap and easy to manufacture and can even be made into spray solutions.
In the new study, researchers at the Ulsan Institute of Science and Technology (UNIST) made some adjustments to the recipe to improve the technology. Quantum dot solar cells made from organic materials are theoretically the most efficient, but unfortunately they have the drawback of being less stable in sunlight and weather conditions, which is not ideal for devices designed to be exposed to sunlight throughout the day. To solve this problem, these solar cells are often replaced with inorganic materials, but this also limits their efficiency.
The UNIST team made quantum dots from organic peroxides and developed a new method of anchoring the quantum dots to the substrate, allowing them to move closer together. This increased efficiency to a record 18.1% from 16.6% in 2020. This record was independently recognized by the US National Renewable Energy Laboratory (NREL).
Even better, the new solar cells are much more stable. Under normal conditions, they can maintain full power for 1,200 hours, and under high temperatures of 80°C (176°F), they can maintain efficiency for 300 hours. They performed equally well after two years in storage.
Quantum dot solar cells still have a long way to go before they can catch up with the silicon solar cells used every day, for which research and development have been half a century ahead and are rapidly approaching their theoretical maximum efficiency. At the same time, quantum dots only really entered the laboratory around 2010, and their efficiency at that time was less than 4%. While improving efficiency, cheap and simple manufacturing processes can help scale the technology to create a wider range of photovoltaic surfaces.
The research was published in the journal Nature Energy.