Investigation on the conversion efficiency of InGaN solar cells fabricated on GaN and ZnO substrates

By the use of a device simulator that takes the quantum effect into account, we have investigated the characteristics of InGaN solar cells stacked coherently on GaN or ZnO substrates. We have found that it is necessary to fabricate nonpolar cells, N-polar cells with p-i-n structures, or III-polar cells with n-i-p structures in order to achieve high conversion efficiency. InGaN solar cells grown on GaN substrates and on ZnO substrates exhibit almost the same conversion efficiencies, in spite of the difference in the intensities of the strains in the InGaN films. Taking the smaller lattice mismatch between InGaN and ZnO into account, we conclude that the use of ZnO substrates, which makes the growth of thick InGaN films with high In concentrations simpler to achieve, is advantageous in the fabrication of high conversion efficiency InGaN solar cells. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim