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Title: Strategies for Thinning Graded Buffer Regions in Metamorphic Solar Cells and Performance Tradeoffs

Abstract

Compositionally graded buffers (CGBs) have enabled the development of inverted metamorphic (IMM) multijunction solar cells that contain three or more junctions and exhibit record efficiencies. Typically, the CGB is grown thick with a constant grading rate, because this is the most straightforward way to minimize the threading dislocation density (TDD) in device active regions. The CGB growth represents a significant expense, in terms of materials consumption and capital cost, however, hampering the economic viability of metamorphic devices. This work explores strategies for thinning Ga1-xInxP CGBs from GaAs to InP while minimizing performance loss, as evaluated by the open-circuit voltage (VOC) of ~0.74 eV Ga0.47In0.53As solar cells. Using the Ga1-xInxP CGB as a model, we demonstrate that slower grading is necessary in certain regions of the grade where dislocation nucleation rates are higher. Grading must be more gradual in these regions to suppress threading dislocation density. Grading rates can be increased in non-critical areas where dislocation nucleation is lower, permitting a thinner buffer. We demonstrate the relationship between VOC and TDD, establishing tradeoffs between thickness and performance. Through careful design, we demonstrate a CGB with a 40% thickness reduction (2 im) achieved with a VOC decrease of only 6.3% (21 mV).

Authors:
 [1];  [1];  [1];  [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
OSTI Identifier:
1461854
Report Number(s):
NREL/JA-5900-70796
Journal ID: ISSN 2156-3381
Grant/Contract Number:  
AC36-08GO28308
Resource Type:
Accepted Manuscript
Journal Name:
IEEE Journal of Photovoltaics
Additional Journal Information:
Journal Volume: 8; Journal Issue: 5; Journal ID: ISSN 2156-3381
Publisher:
IEEE
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; strain; III-V semiconductor materials; indium phosphide; lattices; gallium arsenide; photovoltaic cells; switches

Citation Formats

Schulte, Kevin L., France, Ryan M., Guthrey, Harvey L., and Geisz, John F. Strategies for Thinning Graded Buffer Regions in Metamorphic Solar Cells and Performance Tradeoffs. United States: N. p., 2018. Web. doi:10.1109/JPHOTOV.2018.2841499.
Schulte, Kevin L., France, Ryan M., Guthrey, Harvey L., & Geisz, John F. Strategies for Thinning Graded Buffer Regions in Metamorphic Solar Cells and Performance Tradeoffs. United States. doi:10.1109/JPHOTOV.2018.2841499.
Schulte, Kevin L., France, Ryan M., Guthrey, Harvey L., and Geisz, John F. Fri . "Strategies for Thinning Graded Buffer Regions in Metamorphic Solar Cells and Performance Tradeoffs". United States. doi:10.1109/JPHOTOV.2018.2841499. https://www.osti.gov/servlets/purl/1461854.
@article{osti_1461854,
title = {Strategies for Thinning Graded Buffer Regions in Metamorphic Solar Cells and Performance Tradeoffs},
author = {Schulte, Kevin L. and France, Ryan M. and Guthrey, Harvey L. and Geisz, John F.},
abstractNote = {Compositionally graded buffers (CGBs) have enabled the development of inverted metamorphic (IMM) multijunction solar cells that contain three or more junctions and exhibit record efficiencies. Typically, the CGB is grown thick with a constant grading rate, because this is the most straightforward way to minimize the threading dislocation density (TDD) in device active regions. The CGB growth represents a significant expense, in terms of materials consumption and capital cost, however, hampering the economic viability of metamorphic devices. This work explores strategies for thinning Ga1-xInxP CGBs from GaAs to InP while minimizing performance loss, as evaluated by the open-circuit voltage (VOC) of ~0.74 eV Ga0.47In0.53As solar cells. Using the Ga1-xInxP CGB as a model, we demonstrate that slower grading is necessary in certain regions of the grade where dislocation nucleation rates are higher. Grading must be more gradual in these regions to suppress threading dislocation density. Grading rates can be increased in non-critical areas where dislocation nucleation is lower, permitting a thinner buffer. We demonstrate the relationship between VOC and TDD, establishing tradeoffs between thickness and performance. Through careful design, we demonstrate a CGB with a 40% thickness reduction (2 im) achieved with a VOC decrease of only 6.3% (21 mV).},
doi = {10.1109/JPHOTOV.2018.2841499},
journal = {IEEE Journal of Photovoltaics},
number = 5,
volume = 8,
place = {United States},
year = {2018},
month = {6}
}

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