Sustainable Semiconductors Made From Birch Leaves
Nanoparticles made from pressure-cooked leaves could replace rare elements used in organic semiconductors.
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By pressure-cooking birch leaves, researchers can produce quantum dots with favorable enough optical properties to replace some of the rarer elements used in semiconductors for optoelectronics, a new study suggests.
The new pressure-cooking method, developed by physicists at Umeå University, Sweden, in collaboration with researchers in Denmark and China, can break down plant biomass starting material into nano-sized carbon particles, called carbon quantum dots.
The researchers also report having succeeded in producing a bio-based semiconductor material that makes use of the carbon dots derived from birch leaves. The research is published in the Royal Society of Chemistry journal, Green Chemistry.
Sustainability in semiconductors
Organic semiconductors are one of the most important functional materials being used in electronics. Within optoelectronics, such semiconductors are most notable for powering organic light-emitting diodes (OLEDs), which are used in ultra-thin and bright television and mobile phone screens.
But the increased demand for organic semiconductor technology comes with a big problem – they are mainly produced from petrochemical compounds using unsustainable feedstocks and from rare elements, such as platinum, indium and phosphorus, that require extensive mining operations to source. Neither of these sources for so-called “critical raw materials” are particularly kind to the environment.
To improve the sustainability of the semiconductor industry, researchers are beginning to investigate alternative feedstocks that could be used in place of these critical raw materials.
"The essence of our research is to harness nearby renewable resources for producing organic semiconductor materials," said study author Jia Wang, research fellow in the Umeå University Department of Physics.
In the new study, Wang and her colleagues report the successful creation of a semiconductor that uses bio-based carbon dots as its sole raw material.
From a humble leaf to a quantum material
The synthesis of this new semiconductor is remarkably simple. After picking leaves from the birch trees that grow on the Umeå University campus, the researchers effectively pressure-cooked the leaves in a solvothermal reaction process using ethanol solution.
Drying and extracting this solution yielded “carbon dots” – quantum dots made up of carbon nanomaterials – roughly two nanometers in size. When dissolved in fresh ethanol solution, the carbon dots emitted a narrow-band deep red light.
What is a quantum dot?
Quantum dots are semiconducting particles measuring less than 10 nanometers in size, made up of just a few thousand atoms in total. Due to their small size, their electrons can be affected by strange quantum phenomena, which affects how the particles absorb and release light.
The researchers were able to use the carbon dots in the fabrication of a new light-emitting electrochemical device, capable of generating brightness up to 100 candela per meter squared (cd/m2). This is equivalent to the light intensity given off by an average computer screen.
“It is important to note that our method is not limited to birch leaves” added Wang. "We tested different plant leaves with the same pressure cooking method, and all of them produced similar red-emitting carbon dots. This versatility suggests that the transformation process can be used in different locations.”
Unlike other comparable commercial quantum dots that can be used for semiconductor materials, the new bio-based carbon dots contain no petrochemical compounds, heavy metals or critical raw materials.
“This result shows that it is possible to transition from depleting petroleum compounds to regenerating biomass as a raw material for organic semiconductors,” Wang said.
The team also believe that their bio-based carbon dots could have wider application beyond light-emitting devices.
“Carbon dots are promising across various applications, from bioimaging and sensing to anti-counterfeiting,” Wang said. “We're open to collaborations and eager to explore more exciting uses for these emissive and sustainable carbon dots.”
Reference: Tang S, Liu Y, Opoku H, et al. Fluorescent carbon dots from birch leaves for sustainable electroluminescent devices. Green Chem. 2023;25(23):9884-9895. doi: 10.1039/D3GC03827K
This article is a rework of a press release issued by Umeå University. Material has been edited for length and content.