Solar energy is present in abundance around us. The problem is how to harness a substantial portion of it for human use. How to raise the efficiency bar of solar conversion into electricity? Scientists are continuously engaged in finding a way out for this problem. Recently scientists at the Kyoto Institute of Technology have deviated from the normal path and tried to trap the visible as well as invisible rays of sun for electricity. They tried to create a new photovoltaic cell that can capture visible, infrared and ultraviolet light of the sun. The team now thinks that this photovoltaic will be highly efficient for solar power conversion.
In March, 2010 a meeting was held by the Japan Society of Applied Physics. In this meeting a research group from the Kyoto Institute of Technology talked about their new photovoltaic cell that is capable of generating electricity not only from visible light, but from ultraviolet and infrared light as well. The research group is headed by the associate professor Saki Sonoda. The research group delivered a 90-minute lecture on the cell under the title “Nitride Semiconductor Added With Transition Metals as a Photoelectric Conversion Material for Ultraviolet, Visible and Infrared Lights ~ In the Aim of Realizing the Next-generation Super-efficient PV Cell With a Simple Element Structure.”
Saki Sonoda is quite optimistic that his team’s work would lead towards a more efficient PV cell that can be single-junction rather than the more conventional multi-junction. A multi-junction PV cell has multiple thin films of varying absorption capabilities. This will help in capturing the entire spectrum of light. But with a single-junction cell all that light can be absorbed using a single junction cell.
These new PV cells were made up of gallium nitride (GaN) semiconductor. This new photovoltaic cell is created by ‘doping’ a wide bandgap transparent composite semiconductor i.e. gallium nitride (GaN) with a 3d transition metal such as manganese. Gallium belongs to the family of scandium, titanium, vanadium, chrome, iron, cobalt, nickel, copper, and zinc. Sonoda explained that his team has gone for those additive elements. He said that even aluminum nitride (AlN), which has a very large bandgap, can possibly have an absorbing region in the visible light range,
If we look at the stats we can see that the short-circuit current density of the PV cell is about 10?A/cm2, which is about 1/1,000 that of a normal crystalline silicon PV cell. Sonoda explained that normally the cell and electrodes are separated, therefore the electric resistance of the p-type GaN connecting them is very large. Now we can hope that the findings of the research group are expected to pave the way to a GaN-based PV cell with a totally different mechanism.
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