In order to achieve high efficiency of solar cells, solar spectrum-splitting technique was suggested. On the basis of a previous work of a-Si:H//CIGS splitting solar cells with 22% efficiency, we tried to demonstrate InGaP//CIGS 4-terminal spectrum-splitting structure to reinforce top cell performance instead of using the a-Si:H. After the spectrum-splitting at 620 nm, the InGaP//CIGS 4-terminal cells exhibited an efficiency of 27.4%. With an extension up to a 3-junction by employing a GaAs solar cells as a middle cell, InGaP//GaAs//CIGS spectrum-splitting solar cells were realized and measured by a new current–voltage measurement system using two optical splitters of which splitting wavelengths correspond to 645 and 875 nm. By applying those configurations, the InGaP//GaAs//CIGS solar cells showed 28.9% efficiency after the splitting, and the final efficiency higher than 31.0% was also demonstrated under relatively low-concentration ratio about 10 suns. These results indicate that our spectrum-splitting approach can open promising opportunities to achieve the high efficiency (>30%) with an additional merit of flexible employment of each solar cell without process limitation.
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