Design and characterization of multijunction photovoltaic laser power converters for nonuniform irradiance light profiles

Nonuniform irradiance profiles of lasers used in power-by-light systems deteriorate the efficiency of photovoltaic laser power converters. We analyze three approaches to deal with this efficiency loss: (1) to design the power converter front grid for the nonuniform light received from the power-by-light system; (2) to strengthen the peak current and decrease the series resistance of tunnel junctions; and (3) to homogenize the light spot impinging the power converter by simply distancing it from the laser fiber. In the context of these approaches, this paper tackles the optimization of multijunction photovoltaic laser power converters to achieve their maximum efficiency under nonuniform irradiance profiles, without using any optical element to homogenize them and, this way, reproducing realistic operating conditions. As a direct application of the design shown in this paper, we have increased the experimental efficiency of our GaAs devices by up to 3% absolute for a nominal laser wavelength of 857 nm.