Fundamentals and recent results of super high-efficiency solar cells

摘要

Ⅲ-Ⅴ compound multi-junction (MJ) solar cells have great potential for space and terrestrial applications because they have high efficiency potential of more than 50% and superior radiation-resistance. Recently, more than 40% efficiency cells were reported by Fraunhofer ISE, Spectrolab, Sharp and others. Concentrator 4-junction or 5-junction solar cells have great potential for realizing super high-efficiency of over 50%. In order to realize super high-efficiency of more than 50%, it is substantially important to understand and reduce several losses of solar cells. This paper reviews loss mechanism for Ⅲ-Ⅴ compound solar cells and MJ solar cells. In addition, recent results under the EU-Japan Collaborative Research on Concentrator Photovoltaics are also presented. The conversion efficiency of inverted epitaxially grown InGaP/GaAs/InGaAs triple-junction solar cells has been improved to 37.9% (1-sun, AM1.5G) and 44.4% (250- 300 suns) as a result of proposing double-hetero structure wide-band-gap tunnel junctions, and inverted epitaxial growth.