High-perfomance patterned arrays of core-shell GaAs nanopillar solar cells with in-situ ingap passivation layer

In this work, we present nanostructured core-shell solar cells based on patterned GaAs nanopillars grown by MOCVD. [1] The patterns are photolithographically defined and center-to-center pitch, hole size and mask arrangement can be pre-determined at nanometric resolution. The inherently catalyst-free growth mode eliminates any metal (i.e. Au) diffusion into the nanopillars that could hinder the electron-hole pair extraction. The lattice-matched growth capability also avoids threading dislocations that normally act as recombination centers, worsening the leakage current in pn-junction based devices. Radial-junction-based photovoltaic devices are being actively studied due to the fact that the light absorption (vertical direction) is decoupled from the carrier collection (radial direction), relaxing carrier diffusion length constraints. [2-4] The cylindrical junction area in the nanopillar is increased by several times compared to the equivalent planar footprint counterpart. Furthermore, the periodic arrangement of nanostructures results in greatly enhanced optical absorption. [5] This study aims at evaluating the effect of InGaP as a high-bandgap material to cap GaAs core-shell p-n junctions grown as patterned nanopillar arrays to mitigate any carrier surface recombination. Device characterization is carried out in terms of photocurrent density-voltage (JV) characteristics (under dark and standard AM 1.5 conditions) and external quantum efficiency measurements.