A novel method developed in Tokyo, Japan, allows a nitride crystal to grow, which can function as both an n- and p-type conductor. The material can replace cadmium-telluride (CdTe) in thin films, and make such solar cells more environmentally friendly, while enabling greater efficiencies, the researchers claim.
Researchers from the Tokyo Institute of Technology have shown that copper nitride acts an n-type semiconductor, while fluorine doping provides p-type conduction, according to the institute’s announcement.
A group of researchers led by head researcher, Matsuzaki set out to find new materials for the production of n-type and p-type conductors used in thin film solar cells. During the process, it created a copper nitride crystal, which functions as an n-type conductor. By using a nitriding technique suitable for mass production, this technology could scale at low cost, the team states.
The process is comprised of a computational search for doping elements, atomically resolved microscopy, and electronic structure analysis using synchrotron radiation.
The new material is a compound – copper nitride – which, the researchers say is environmentally friendly. Usually occurring difficulties that occur when attempting to grow nitride crystals were reportedly addressed as the team used a novel catalytic reaction route, which employed ammonia and oxidant gas.
The compound creates an n-type conductor with excess electrons. If this compound is then treated with a fluorine element, it can transform into a p-type conductor. The process was previously established in theoretical calculations, and has now been proven via the use of atomically resolved microscopy.
Solar cells need an n-type and p-type partner, and the configuration of the two has been the subject of solar cell research, the institute claims in its announcement. By sourcing both conductors from the same material, the team alleges that more efficient solar cells can be produced with this type of conductor.
Thin film production has been overshadowed by its use of cadmium, as the material is categorized as highly toxic and any contamination with the environment must be avoided.
In 2010, the material was banned under the EU’s RoHS regulation, though an exemption for solar cells was made. The exemption has garnered a lot of criticism from institutes and renowned researchers, who insist it cannot be fully ruled out that trace amounts of the material can exit the panels and contaminate the environment.
Since then, research institutes and solar cell developers have sought to establish new materials to be used and n- and p-type conductors in thin film solar cells.
Source PV Magazine