A comparative simulation study of InGaP/GaAs multi-junction solar cells in two-, three-, and four-terminal configurations

This study presents a comparative computational analysis of four-terminal (4T), two-terminal (2T), and three-terminal bipolar transistor (3T) InGaP/GaAs multijunction solar cells under a unified simulation framework with standard one-sun illumination (AM1.5 G, 300 K). Layer thickness variations are systematically optimized to evaluate their impact on performance. The 4T configuration achieves the highest efficiency (37.40%) with window/Back-Surface Field layers under the idealized assumption of zero surface reflection, benefiting from decoupled sub-cell operation. The 2 T tandem reaches 36.38% but is constrained by current matching, while the 3T-heterojunction bipolar transistor solar cell attains 31.06% with simplified epitaxy. The 2T configuration exhibits the largest absolute efficiency gain (+11.48%) from passivation due to relaxation of the current-matching constraint. These results quantify the trade-offs between efficiency, complexity, and design flexibility, providing guidance for architectural selection in advanced photovoltaics.