Sulfur passivation and contact methods for GaAs nanowire solar cells

Abstract

The effect of sulfur passivation on core-shell p-n junction GaAs nanowire (NW) solar cells has been investigated. Devices of two types were investigated, consisting of indium tin oxide contact dots or opaque Au finger electrodes. Lateral carrier transport from the NWs to the contact fingers was achieved via a p-doped GaAs surface conduction layer. NWs between the opaque contact fingers had sidewall surfaces exposed for passivation by sulfur. The relative cell efficiency increased by 19% upon passivation. The contribution of the thin film grown between the NWs to the total cell efficiency was estimated by removing the NWs using a sonication procedure. Mechanisms of carrier transport and photovoltaic effects are discussed on the basis of spatially resolved laser scanning measurements.

GaAs nanopillar-array solar cells employing in situ surface passivation

“…Conversely, rectifying contacts resulting from parasitic Schottky barriers can create wide depletion regions, forcing the carriers to overcome the potential barrier by thermionic emission42. Despite fundamental, these transport properties at the electrode interface have been so far overlooked, and only a few theoretical reports discuss these effects in GaAs nanowire-based solar cells43. With metals, Ti/gold ohmic contacts to p-GaAs are routinely achieved with very low resistance44, without requiring any thermal annealing step.…”

Strong surface passivation of GaAs nanowires with ultrathin InP and GaP capping layers

“…The shell growth can be avoided by passivating the surface with sulfur, but that method has been reported to suffer from stability issues. 12 We report here an alternative, simple passivation method for GaAs nanowires based on an in-situ grown ultrathin InP or GaP capping layer. We show that already a few-monolayer (ML) thick capping layer provides efficient passivation without need to grow shells with a thickness of several nanometers.…”

Raman spectroscopy of GaP/GaNP core/shell nanowires

“…[1][2][3][4] Recent advances in growth techniques have made it possible to vary chemical compositions either axially along the NW's length or radially, i.e., by growing surrounding shells of different materials resulting in core/shell NW structures. [5][6][7] The latter approach is very promising for fabrication of photovoltaic devices, since it can improve the efficiency of optical absorption and charge collection in vertically aligned NW arrays.…”