Simulation of a through cell via contacts architecture for HCPV multi-junction solar cells

Abstract

In this study we quantify the possible gains in cell performance obtained with an architecture based on through-cell via contacts (TCVC). We review how the front metallization of solar cells introduces a compromise between shadowing and resistive losses. The work models the trade-offs that directly impacts the device efficiency. Gains at the cell level are important because they are highly leveraged in HCPV systems. For a very high illumination flux, a standard cell optimization leads to a large metallized area for finger grid designs. Our modeling shows that the back-contact architectures can offer an interesting alternative. The TCVCs were evaluated using a multijunction InGaP/InGaAs/Ge solar cell (MJSC). The proposed architecture is modeled and compared with a conventional grid design. The absolute efficiencies of the different solar cells were calculated to quantify their shadowing and resistive losses. A combination of finite-element modeling and equivalent-circuit calculations were used. Our study finds that an absolute efficiency improvement of 1.8% could be obtained over a conventional MJSC design by using a basic via contact design for a light concentration of 2000 suns. This gain attains 3.0% when cross-fingers are added to the design. Furthermore, we show that the TCVCs are expected to be a cost-effective solution because the removal of bus bars area improves significantly the wafer utilization. The latter improvement is estimated to result in an increase in power generation of about 20% per wafer.