What is it about?
We show a procedure to increase the reproducibility of multi-junction solar cell production. This is achieved by applying a systematic offset to room-temperature photoluminescence measurements to match the required band gap for obtaining current match as simulated by optical modelling. We found that the difference in band gap extracted from photoluminescence and external quantum efficiency respectively is systematic and depends on the material system under investigation. With the help of this procedure, we modelled and built a 4-junction solar cell that reaches a power conversion efficiency of 43.6 % under the AM1.5d solar spectrum that was 710-fold concentrated.
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Why is it important?
Multi-junction solar cells are very susceptible to changes of the subcell photocurrents. If these are not matched the overall current will be reduced and some of the solar resource is wasted. Hence, it is vital to tune the band gap and thickness of all involved absorber materials, both of which determine absorption and thus the subcell photocurrent, very carefully using simple test structures prior to epitaxial growth of a multi-junction solar cell.
Perspectives
I am convinced that we need high-efficiency solar cells in order to obtain a sustainable energy supply system. I believe that concentrating photovoltaics using multi-junction solar cells is the technology with the lowest environmental footprint thanks to the low area and resource demand. We are committed to bringing the costs further down for this technology so that it is not only ecologically but also economically viable. I hope this article will be useful for everybody who is concerned with epitaxial growth of solar cells with multiple absorbers.
Patrick Schygulla
Fraunhofer ISE
Read the Original
This page is a summary of: Increasing transferability between design and epitaxial growth of multi-junction solar cells, January 2022, American Institute of Physics,
DOI: 10.1063/5.0099724.
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