We developed a straightforward method based on detailed balance relations to analyze individual subcells in multi-junction solar cells via measuring absolute electroluminescence quantum yields. This method was applied to characterization of a InGaP/GaAs/Ge 3-junction solar cell for satellite use. In addition to subcell I-V characteristics and internal luminescence yields, we derived balance sheets of energy and carriers, which revealed respective subcell contributions of radiative and nonradiative recombination losses, junction loss, and luminescence coupling. These results provide important diagnosis and feedback to fabrications. We calculated conversion-efficiency limit and optimized bandgap energy in 2-, 3-, and 4-junction tandem solar cells, including finite values of sub-cell internal luminescence quantum yields to account for realistic material qualities in sub-cells. With reference to the measured internal luminescence quantum yields, the theoretical results provide realistic targets of efficiency limits and improved design principles of practical tandem solar cells.

Date Published: 16 March 2015
PDF: 8 pages
Proc. SPIE 9358, Physics, Simulation, and Photonic Engineering of Photovoltaic Devices IV, 93580B (16 March 2015); doi: 10.1117/12.2175825

Published in SPIE Proceedings Vol. 9358:
Physics, Simulation, and Photonic Engineering of Photovoltaic Devices IV
Alexandre Freundlich; Jean-François Guillemoles; Masakazu Sugiyama, Editor(s)