Comprehensive Electrical Loss Analysis of Monolithic Interconnected Multi-Segment Laser Power Converters

A method for distributed electrical modeling of complete photovoltaic monolithic interconnected modules (MIMs) with complex geometrical and electrical features is developed and applied to study electrical power losses of a six-segment GaAs-based MIM laser power converter (LPC). The model considers spatial dependence of resistive and recombination losses of all epitaxial layers and explicitly takes into account perimeter recombination and the photo-induced leakage current through the semi-insulating GaAs substrate. The investigated specimen was fully parametrized to obtain the model's input parameters which were verified by a comparison of a variety of simulated and measured specimen's electrical characteristics. Based on simulations, we show that distributed series resistance effects, mainly caused by Joule heating in the lateral conduction layer (LCL), limit the efficiency of MIM LPCs under a high irradiance illumination, whereas for a low irradiance illumination perimeter recombination is identified as the limiting factor. Additionally, photo-induced conductivity leads to a reciprocal relationship between irradiance and substrate resistivity, which results in a parasitic shunting between segments and reduces the device efficiency. We present mitigation strategies for the outlined major loss mechanisms and propose a thin-film cell employing a metal back mirror that exploits photon recycling and mitigates LCL losses. With such MIM LPC design, conversion efficiencies above 60% can be reached for a broad irradiance range.