Transfer Of Power By Photons In HCPV Triple-Junction Cells

摘要

We report the results on measurements of electroluminescence and photocurrent, arising due to photoexitation of the top sub-cell of an InGaP/GaAs/Ge solar cells by focused light from the green laser (X=532 nm). The excitation intensity was chosen in such a way, that it would produce the photocurrent equal to that flowing through the top p-n junction under conditions of 500x-concentrated sunlight illumination and connection to the optimum external load (5÷10% of short-circuit current value). There existed two luminescent signal: first one due to photoluminescence (PL) at recombination of photogenerated charge carriers not collected by the p-n junction; second one due to electroluminescence (EL) at recombination of carriers, collected by the p-n junction, and injected backward under open-circuit conditions. They could be measured separately owing to difference in the spatial distribution along the cell surface. Photocurrent, induced in the middle GaAs sub-cell by the top sub-cell EL was measured by comparison of their IR signal with a similar signal arising at passing the forward current through a triple-junction cell. The photocurrent, induced by transfer of EL from the GaAs sub-cell to the bottom Ge sub-cell was measured as the short-circuit current of a triple-junction cell. It was found that, in operational conditions of the HCPV InGaP/GaAs/Ge solar cells, transfer of the excitation power from top to middle and from middle to bottom sub-cells takes place at a level of about 5%. This process results in corresponding increase in excitation intensity of two latter sub-cells in comparison with the conditions expected from sun spectrum intervals, suitable for the materials of these sub-cells.