Multilayer-Grown Ultrathin Nanostructured GaAs Solar Cells

We present multilayer-grown ultrathin singlejunction GaAs solar cells with uniform photovoltaic performance. Triple-stack ultrathin GaAs solar cells were grown by molecular beam epitaxy (MBE) using beryllium as a p-type dopant. Microscale solar cells with a vertical contact configuration exhibited excellent uniformity (<;3%) of performance among top, middle, and bottom device layers due to the suppressed diffusion of p-type impurity and reduced time for epitaxial growth. Microcells implemented with hexagonally periodic TiO2 nanoposts and metal reflector provided significantly improved performance owing to the optimized bifacial photon management, where 20.8% efficiency was obtained from 420-nm thick GaAs solar cells.