Improving the Open-Circuit Voltage of III-V Layer-Filtered Si Subcells for Monolithic III-V/Si Tandem Solar Cells

Abstract

Monolithically integrated III-V/Si multijunction solar cells are promising for highly reliable, scalable, and efficient photovoltaic cells. However, growth of III-V materials at high temperatures degrades the open-circuit voltage of Si subcells primarily due to reduced Si bulk minority carrier lifetimes. Here, we report a systematic study of open-circuit voltage improvements from 0.505 to 0.539 V in 2 mu m thick GaAs layer-filtered Si subcells by employing SiO2/SiNx protection layers during III-V molecular beam epitaxy (MBE) growth and by serving them as surface passivation. Cells with the protection layers exhibit a Si bulk minority carrier lifetime of 180 mu s after III-V MBE growth, which is about 9 times higher than those (21 mu s) without protection layers. A 1.65 eV, Al0.18Ga0.82As buffer-filtered Si subcell reveals 0.548 V and is compared with those of previous III-V/Si tandem studies. This study presents a practical approach to realizing high-performance Si subcells for monolithically integrated high-efficiency III-V/Si tandem solar cells.