Increased efficiency in multijunction solar cells through the incorporation of semimetallic ErAs nanoparticles into the tunnel junction

Abstract

We report the molecular beam epitaxy growth of Al0.3Ga0.7As∕GaAs multijunction solar cells with epitaxial, semimetallic ErAs nanoparticles at the interface of the tunnel junction. The states provided by these nanoparticles reduce the bias required to pass current through the tunnel junction by three orders of magnitude, and therefore drastically reduce the voltage losses in the tunnel junction. We have measured open-circuit voltages which are 97% of the sum of the constituent cells, which result in nearly double the efficiency of our multijunction cell with a conventional tunnel junction.

Cross-sectional scanning tunneling microscopy and spectroscopy of semimetallic ErAs nanostructures embedded in GaAs

“…4 Among such structures, ErAs nanoparticles embedded within GaAs are one of the most widely studied.…”

High‐performance nanoparticle‐enhanced tunnel junctions for photonic devices

“…They have enhanced the performance of AlGaAs/GaAs tandem solar cells [10]. The performance of the top (AlGaAs) cell indicates that high-quality III-V material may be grown over ErAs; however this has not been directly investigated.…”

Effects of nanoscale embedded Schottky barriers on carrier dynamics in ErAs:GaAs composite systems

“…The composite systems display tunable photo-carrier relaxation with ultrashort relaxation times spanning two orders of magnitude 3,6 , while achieving greater film quality 1,7-9 and transport characteristics than low temperature grown GaAs 1,10-16 . These features have made the ErAs:GaAs system highly promising for integration into GaAs-based opto-electronic devices 6,14,[17][18][19][20][21] . However, the fundamental relaxation phenomena of these systems must be fully characterized before such applications can be realized.…”

“…The slope of the band tails is also observed to increase with ErAs volume fraction (a figure of the band tail slopes can be found in the Supplemental Material), indicating an increase in the density of interface states with ErAs incorporation. The interface between metallic ErAs and semiconducting systems are known to create localized traps, or Schottky barriers 14,21,25,26 , with different barrier heights depending on the crystallographic directions of the interface 27 . The interface states are partiality occupied and extend into the GaAs matrix 13,22 , providing a route for the carriers to move from the interface into the GaAs host.…”