Optimizing multijunction photonic power converter design with measured radiative efficiency

Photonic power converters (PPCs) are multijunction photovoltaic devices that convert monochromatic light to electricity. We measure the current-density-dependent external radiative efficiency of representative single-junction GaAs PPCs and use the results in a multijunction detailed balance model to predict attainable device efficiencies in multi-junction GaAs PPCs. For fixed input optical power density, we determine the number of junctions that maximizes efficiency, including effects of luminescent coupling and series resistance. The optimal number of junctions ensures that the device operates close to its maximum radiative efficiency.