Analysis of defects and impurities in new (In)GaAsN materials for concentrator multi-junction solar cells

Abstract

Target of the Japanese Innovative Photovoltaics R&D Program started from fiscal year 2008 is to develop high efficiency solar cells with conversion efficiency of more than 40% and low electricity cost of less than 7 JPY/kWh until 2050. In this program, concentrator III–V compound multi-junction (MJ) tandem solar cells have great potential for high efficiencies of over 50% and low cost of less than 30JPY/W. InGaAsN material is good candidate for 4–6 junction solar cells. In our preliminary stage of our project, 2% and 11.3% efficiencies have been obtained with GaAsN p-n and InGaAsN p-i-n single-junction solar cells. In order to increase efficiency of single and 4-junction solar cells, it is very important to understand and reduce defects and impurities in the grown films. In this paper, characterization of the CBE (Chemical Beam Epitaxy)-grown GaAsN films by Hall effect and DLTS (Deep Level Transient Spectroscopy) measurements is presented.