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Title:
 
The Effects of Short-Range Alloy Disorder on the Potential Voltage Performance in GaAsBi Based Solar Cells
 
Author(s):
 
T. Wilson, A. Mellor, N.P. Hylton, N.J. Ekins-Daukes
 
Keywords:
 
High Efficiency Solar Cells, Multijunction, Alloy Disorder, GaAsBi
 
Topic:
 
Concentrator and Space Photovoltaics
Subtopic: III-V-Based Devices for Terrestrial and Space Applications
Event: 33rd European Photovoltaic Solar Energy Conference and Exhibition
Session: 4CV.4.11
 
Pages:
 
1257 - 1263
ISBN: 3-936338-47-7
Paper DOI: 10.4229/EUPVSEC20172017-4CV.4.11
 
Price:
 
 
0,00 EUR
 
Document(s): paper
 

Abstract/Summary:


The large band-gap bowing induced by the incorporation of Bi allows GaAsBi to achieve direct gap energies around 1.0 eV for relatively dilute quantities of Bi, which makes the material attractive as a potential middle sub-cell for future multi-junction solar cells. However, the presence of band-tail states due to inherent short-range alloy disorder may have an adverse effect on voltage performance and optimum sub-cell energies. In this work a range of GaAsBi samples are examined with varying Bi fractions between 0 and 9.7%. A broadening of the fundamental critical point is observed for Bi fractions up to 5.5%, indicative of short-range alloy disorder induced by increased Bi incorporation. Open-circuit voltage performance is observed to degrade in GaAsBi samples with Bi in excess of 4%, which corresponds to band-gap energies in the vicinity of 1.0 eV. Detailed balance calculations incorporating a broadened absorption edge indicate a reduction in maximum efficiency and a blue-shift of the optimum band-gap energy in both single and quad-junction devices. The subsequent blue-shift of optimum bottom cell energy with increased lower-middle cell broadening highlights the potential influence of disordered alloys on optimum multijunction solar cell design.