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 μm thick GaAs layer-filtered Si subcells by employing SiO₂/SiN_x 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 μs after III–V MBE growth, which is about 9 times higher than those (21 μs) without protection layers. A 1.65 eV, Al_0.18Ga_0.82As 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.