Eugene A. Katz, Ph.D. Department of Solar Energy & Environmental Physics and Ilse-Katz Institute for Nanoscale Science & Technology, Ben-Gurion University of the Negev, Israel
With today’s ultra-efficient photovoltaics (PV) having attained close to their basic limit for current generation and fill factor, the path to higher efficiency - approaching and even surpassing the Shockley-Queisser limit - is via enhancing open-circuit voltage Voc. Two strategies for improving ultra-efficient PV performance via Vocenhancement are: (1) optical concentration of sunlight – a key rationale for concentrator PV (CPV), and (2) external photon recycling.
In the first part of the talk, I will review our experimental results on operation of CPV cells under ultra-high concentration of sunlight (up to 10,000 suns) . Although this strategy has been successfully realized, an equally potent alternative is decreasing the cell’s recombination current – an aim that can be achieved by externally recycling cell photon emission. While the theory for the potential benefit of photon recycling has recently been elucidated, experimental proof-of-concept had proven elusive - requiring a photovoltaic device possessing a high external luminescent efficiency combined with efficient light recycling optics. I will report experimental evidence of enhancing the performance of today’s champion single-junction commercial GaAs cells  by external recycling of photon emission from the cell’s front surface . Possibility for using this approach for solar cells based on such a novel highly luminescent semiconductor as halide perovskite will be discussed as well. Finally, prospects and open challenging problems for both approaches (solar concentration vs photon recycling) will be compared.