GaAs/AlGaAs Nanowire Array Solar Cell Grown on Si with Ultrahigh Power-per-Weight Ratio

Anjan Mukherjee,Helge Weman,Bjørn-Ove Fimland,Dingding Ren,Junghwan Huh,Per-Erik Vullum

doi:10.1021/acsphotonics.1c00527

Anjan Mukherjee, Helge Weman + Show 4 more

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https://doi.org/10.1021/acsphotonics.1c00527

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Abstract

Here we demonstrate a more effective use of III–V photoconversion material to achieve an ultrahigh power-per-weight ratio from a solar cell utilizing an axial p-i-n junction GaAs/AlGaAs nanowire (NW) array grown by molecular beam epitaxy on a Si substrate. By analyzing single NW multicontact devices, we first show that an n-GaAs shell is self-formed radially outside the axial p- and i-core of the GaAs NW during n-core growth, which significantly deteriorates the rectification property of the NWs in the axial direction. When employing a selective-area ex situ etching process for the n-GaAs shell, a clear rectification of the axial NW p-i-n junction with a high on/off ratio was revealed. Such a controlled etching process of the self-formed n-GaAs shell was further introduced to fabricate axial p-i-n junction GaAs NW array solar cells. Employing this method, a GaAs NW array solar cell with only ∼1.3% areal coverage of the NWs shows a photoconversion efficiency of ∼7.7% under 1 Sun intensity (AM 1.5G), which is the highest achieved efficiency from any single junction GaAs NW solar cell grown on a Si substrate so far. This corresponds to a power-per-weight ratio of the active III–V photoconversion material as high as 560 W/g, showing great promise for high-efficiency and low-cost III–V NW solar cells and III–V NW/Si tandem solar cells.

Highlights

We demonstrate a more effective use of III−V photoconversion material to achieve an ultrahigh power-per-weight ratio from a solar cell utilizing an axial p-i-n junction GaAs/AlGaAs nanowire (NW) array grown by molecular beam epitaxy on a Si substrate
We present an ex situ radial shell-etching process applied to axial p-i-n junction GaAs/AlGaAs NWs grown by molecular beam epitaxy (MBE), leading to clear rectification behavior with high on/off ratio in both single NW and NW array solar cell devices
A highly controlled and homogeneous shell etching along the NW length can be observed in a symmetrically shell-etched type I single NW using a multicontact single NW device (see Figure S1(a, b) in the Supporting Information), in which the hexagonal morphology of the NW is found to be intact throughout the shell-etched region

Summary

Introduction

We demonstrate a more effective use of III−V photoconversion material to achieve an ultrahigh power-per-weight ratio from a solar cell utilizing an axial p-i-n junction GaAs/AlGaAs nanowire (NW) array grown by molecular beam epitaxy on a Si substrate. NW interaction can be controlled by both the NW geometry and the pitch of the NW array in order to enhance the solar cell efficiency beyond the Shockley−Queisser theoretical limit from a single planar junction solar cell.[2−6] In addition, the nanoscale footprints of NWs can accommodate lattice mismatch efficiently, resulting in a superior quality of the interface for heteroepitaxial integration and, for example, allow for high-performance III−V semiconductors on a Si platform.[7−9] Since the first demonstrations of self-catalyzed GaAs NW growth by molecular beam epitaxy (MBE)[10−13] with high crystal phase purity through catalyst contact angle engineering[14,15] and compositional modulation,[16,17] significant efforts have been made to achieve high GaAs NW solar cell efficiencies on Si substrates.[18−20] MBE has shown an excellent capability for both high-efficiency solar cells in thin-film architecture with an axial p-i-n junction and monolithic integration of III−V NWs on Si, most of the reported NW solar cells grown on Si using MBE have radial p− n junctions.[18−22] Considering the state-of-the-art axial junction GaAs NW devices[23,24] and their flexibility in forming a dualjunction tandem structure monolithically on a Si solar cell, the highest solar cell performance is most likely to be achieved if the GaAs NWs are realized through self-catalyzed MBE growth due to the very high structural quality of the NWs with this method

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