Cheaper and more efficient metal-based solar cells to aid wider adoption of alternative sources of energy are coming soon, say Rice University researchers from the Laboratory for Nanophotonics (LANP). Their new solution proposes the use of surface plasmons to increase the potency of photovoltaic devices by bolstering light-matter interactions. This could hugely impact how sunlight is transformed into fuel or electricity.
Plasmons are quantizations of plasma oscillations or Langmuir waves. They refer to rapid oscillations of the electron density in conducting materials such as plasmas or metals. The Rice University team suggests utilizing charge density oscillations of conduction electrons of metallic nanostructures in order to deliver less expensive, but more efficient metal-based solar cells for obtaining green energy.
Published in Nature Communications early this month, the study talks about a new way in which light-capturing nanomaterials can be integrated within solar panels. When light is shone on a metallic nanoparticle or nanostructure, some subset of electrons in the metal are excited to a much higher energy level. The hot carriers or hot electrons could show great potential in solar-energy applications because they can help build devices which produce direct current.
Hot carriers may also come in handy for inducing chemical reactions on otherwise inert metal surfaces. Currently, even the most efficient photovoltaic cells depend on a combination of semiconductors made from rare and expensive elements such as gallium and indium. Plasmonic nanostructures with low-cost semiconductors like metal oxides might be able to offer a cheaper alternative and their optical properties can be controlled with great accuracy.
LANP graduate student Bob Zheng, experimented with two types of devices, each with a plasmonic gold nanowire seated on top of a semiconducting layer of titanium dioxide. A layer of pure titanium was inserted between the gold and the titanium dioxide, in one case. The other model had the gold and the semiconductor in direct contact. Only hot electrons were allowed to pass in the second mentioned example, while all electrons were able to go through, in the first.
This proved that hot electrons were not correlated with total absorption, and were driven by another plasmonic mechanism called field-intensity enhancement. According to the researchers, the finding holds hope of a method to boost the efficiency of plasmonic hot carrier devices, which should ultimately assist in harvesting solar energy for usable electricity.