Researchers from Australia’s Griffith University have discovered a new mechanism for improving the light harvesting properties of certain nanomaterials.
It’s a breakthrough they say could herald a new class of composite materials for enhanced solar absorption and optoelectronics.
The researchers have shown for the first time that a phenomenon known as “quantum-confined bandgap narrowing” enables UV solar energy absorption of titanium oxide (TiO2) and graphene quantum dots to easily extend into the visible light range.
This makes a big difference in terms of energy output, as visible light makes up 43 percent of solar energy compared to only 5 percent emitted by UV light.
According to Dr Qin Li, Associate Professor in the Environmental Engineering & Queensland Micro- and Nanotechnology Centre, potential real-life applications of this would be the production of high-efficiency paint-on solar cells and solar-powered water purification.
“Wherever there is abundant sun we can brush on this nanomaterial to harvest solar energy to create clean water,” Dr Qin Li says.
“This mechanism can be extremely significant for light harvesting. What’s more important is we’ve come up with an easy way to achieve that, to make a UV absorbing material to become a visible light absorber by narrowing the bandgap.”
Titanium oxide nanoparticles are used in the production of dye-sensitised solar cells. Also known as titania, the material is cheap and abundant, and in larger forms is the primary pigment in white paint.
Major efforts have been made to improve the ability of titania to absorb visible light, including metal ion doping, carbon doping, nitrogen doping and hydrogenation; all methods that require extreme temperatures and pressures.
In research published in Chemical Communications, a Royal Society of Chemistry journal, the Griffith Uni team found that mixing titania particles with graphene quantum dots produced a composite material capable of absorbing visible light by a quantum confined bandgap narrowing mechanism.
“We were really excited to discover this: when two UV absorbing materials, namely TiO2 and graphene quantum dots, were mixed together, they started to absorb in the visible range, more significantly, the bandgap can be tuned by the size of graphene quantum dots,” says Dr Li.
“We named the phenomenon ‘quantum-confined bandgap narrowing’ and this mechanism may be applicable to all semiconductors, when they are linked with graphene quantum dots. Flexible tuning of bandgap is extremely desirable in semiconductor-based devices.”