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perfectly reflecting (minority carrier) contacts. The magnitude of these non-radiative recombination losses can be characterized by the internal fluorescence efficiency  * reflections from the front surface (non-ideal ARC): For ideal materials the burden of high open- circuit voltage, and thereby high efficiency, lies with optical design: The solar cell must be designed for optimal light extraction under open-circuit conditions. (Physics required to approach SQ)  * non-ideal back contact reflection (<100%): The Shockley- Queisser limit gets a significant boost from the perfect photon recycling that occurs in an ideal system. Unfortunately, for most materials, their relatively low internal fluorescence yields mean that the upper bounds on their efficiencies are much lower than the Shockley-Queisser limit. For the few material systems that are nearly ideal, such as GaAs, there is still a tremendous burden on the optical design of the solar cell. A very good rear mirror, for example, is of the utmost importance. In addition, it becomes clear that realistic material radiative efficiencies must be included in a credible assessment of any materials‟ prospects as a solar cell technology. (Physics required to approach SQ) The escape of photons through the front surface is an impor-tant loss mechanism in these cells. The escape cone depends onthe ambient index,n, but diffraction effects in the ARC are ex-pected to increase the escape cone somewhat. Photon transportthrough the ARC is not treated. Instead, we use an ambient in-dex ofn=1.35 in an attempt to mimic transmission through thestack of GaAs/ARC (160 nm)/Air by making the front escapecone slightly larger than that of air/GaAs interface. ("Design Solar Cell Close to QS" page 739) The escape of photons through the front surface is an impor-tant loss mechanism in these cells. The escape cone depends onthe ambient index,n, but diffraction effects in the ARC are ex-pected to increase the escape cone somewhat. Photon transportthrough the ARC is not treated. Instead, we use an ambient in-dex ofn=1.35 in an attempt to mimic transmission through thestack of GaAs/ARC (160 nm)/Air by making the front escapecone slightly larger than that of air/GaAs interface. ("Design Solar Cell Close to QS" page 741)  * incomplete absorption (realistic refractive index)  * contact shadowing  * temperature: In the case of low-bandgap solar cells designed for one-sun illumination, particular care should be brought towards(1) minimizing non-radiative recombination losses, whichcan be achieved by advanced growth processes, for example,and (2) ensuring efficient cooling of the cell (solar cell tem-perature can potentially reach tens of degrees above the am-bient temperature under one-sun illumination, a temperaturelevel already high enough to cause a significant degradationin the ability of the cell to reach its theoretical limit accord-ing to our calculations). In contrast, cell over-heating doesnot appear to be a major limiting factor under moderate orhigh illumination levels, the degradation of the SQ indexbecause of temperature being mitigated by sunlight concen-tration. These conclusions emphasize the counter-intuitivefact that the temperature of the cell should particularly be aconcern for “one-sun solar cell” manufacturers.(SQ Limit JAP2015.PDF- in discussion section)