Improved photovoltaic efficiencies by incorporating an internal front reflector in addition to an ideal back reflector is limited to devices with absorber bandgaps below ~1.34 eV due to the availability of AM1.5G photons above the reflector energy-cutoff, i.e. reflector bandgap. However, energy-selective front reflectors especially benefit photovoltaic devices under monochromatic illumination, i.e. laser power converters (LPCs). The efficiency improvements with and without a front reflector as a function of solar cell bandgap are compared under AM1.5G versus monochromatic light at the reflector bandgap. For a GaAs solar cell, where front reflectance enhancements are negligible, over 5% absolute efficiency increase is predicted in a GaAs LPC with a front reflector (605 nm illumination). Bandgap reduction further increases the efficiency enhancement under monochromatic illumination, where up to 60% relative efficiency increase can be achieved at Eg =0.5 eV with E_laser = 1.467 eV.
Silicon solar cells benefit from an internal Lambertian light distribution achieved through texturing, while the performance of direct-bandgap materials can be lower with an internal Lambertian light distribution than the light distribution of a planar cell. A novel analytic expression is derived for the emittance of cells with a Lambertian light distribution and partial rear reflectance. This expression enables comparison of Si, GaAs, CdTe, and CIS cells under planar and Lambertian light distributions with varying rear reflectance in the Auger limit. A Lambertian light distribution is shown to be particularly beneficial to thinner material with higher rear reflectance due to absorptance enhancement. It is found that a Lambertian light distribution increases radiative recombination in most absorbers but can reduce radiative recombination in some CIS material.
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