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Title: Internal Resistive Barriers Related to Zinc Diffusion During the Growth of Inverted Metamorphic Multijunction Solar Cells

Abstract

Majority carrier barriers at heterointerfaces are a common source of non-linear resistance that hinders concentrator solar cell performance. The source of a particular barrier is often unclear in a multijunction device with numerous heterointerfaces. In this work, we demonstrate Zn-dopant diffusion during inverted metamorphic multijunction (IMM) device growth to be one key cause of internal barrier formation. Using an inverted GaAs/GaAs tandem solar cell with a high temperature annealing layer grown in between each subcell, we simulate the annealing conditions of a multijunction growth in a simplified structure. Through analysis of the device by secondary ion mass spectrometry (SIMS) and electrochemical capacitance-voltage profiling, we show that annealing causes Zn to diffuse out of the top cell Ga 0.5 In 0.5 P back surface field (BSF) and accumulate in the GaAs base. Through equilibrium band modeling, we show that the resultant doping profile forms an energetic barrier to hole flow in the valence band, which correlates with fill factor losses in the current-voltage curves measured under concentration. When we, instead, employ a C-doped Al 0.2 Ga 0.8 As BSF layer in the top cell, we do not observe evidence of a heterojunction barrier. We attribute this difference to the reduced diffusivitymore » of carbon, confirmed by SIMS, as well as more favorable valence band offsets between GaAs and Al 0.2 Ga 0.8 As. Finally, we compare 5-junction IMM cells with Al 0.2 Ga 0.8 As:C and Ga 0.5 In 0.5 P:Zn BSF layers in the GaAs third junction, respectively, and show a significantly improved concentrator device performance when Al 0.2 Ga 0.8 As:C is employed. Lastly, we demonstrate the importance of designing annealing tolerance into multijunction structures that are subjected to extended annealing during growth.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. National Renewable Energy Laboratory (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:
1485558
Report Number(s):
NREL/JA-5900-70828
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: 9; Journal Issue: 1; Journal ID: ISSN 2156-3381
Publisher:
IEEE
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; gallium arsenide; zinc; junctions; annealing; photovoltaic cells; photonic band gap; current measurement

Citation Formats

Schulte, Kevin L., Steiner, Myles A., Young, Matthew R., and Geisz, John F. Internal Resistive Barriers Related to Zinc Diffusion During the Growth of Inverted Metamorphic Multijunction Solar Cells. United States: N. p., 2018. Web. doi:10.1109/JPHOTOV.2018.2878317.
Schulte, Kevin L., Steiner, Myles A., Young, Matthew R., & Geisz, John F. Internal Resistive Barriers Related to Zinc Diffusion During the Growth of Inverted Metamorphic Multijunction Solar Cells. United States. doi:10.1109/JPHOTOV.2018.2878317.
Schulte, Kevin L., Steiner, Myles A., Young, Matthew R., and Geisz, John F. Mon . "Internal Resistive Barriers Related to Zinc Diffusion During the Growth of Inverted Metamorphic Multijunction Solar Cells". United States. doi:10.1109/JPHOTOV.2018.2878317.
@article{osti_1485558,
title = {Internal Resistive Barriers Related to Zinc Diffusion During the Growth of Inverted Metamorphic Multijunction Solar Cells},
author = {Schulte, Kevin L. and Steiner, Myles A. and Young, Matthew R. and Geisz, John F.},
abstractNote = {Majority carrier barriers at heterointerfaces are a common source of non-linear resistance that hinders concentrator solar cell performance. The source of a particular barrier is often unclear in a multijunction device with numerous heterointerfaces. In this work, we demonstrate Zn-dopant diffusion during inverted metamorphic multijunction (IMM) device growth to be one key cause of internal barrier formation. Using an inverted GaAs/GaAs tandem solar cell with a high temperature annealing layer grown in between each subcell, we simulate the annealing conditions of a multijunction growth in a simplified structure. Through analysis of the device by secondary ion mass spectrometry (SIMS) and electrochemical capacitance-voltage profiling, we show that annealing causes Zn to diffuse out of the top cell Ga 0.5 In 0.5 P back surface field (BSF) and accumulate in the GaAs base. Through equilibrium band modeling, we show that the resultant doping profile forms an energetic barrier to hole flow in the valence band, which correlates with fill factor losses in the current-voltage curves measured under concentration. When we, instead, employ a C-doped Al 0.2 Ga 0.8 As BSF layer in the top cell, we do not observe evidence of a heterojunction barrier. We attribute this difference to the reduced diffusivity of carbon, confirmed by SIMS, as well as more favorable valence band offsets between GaAs and Al 0.2 Ga 0.8 As. Finally, we compare 5-junction IMM cells with Al 0.2 Ga 0.8 As:C and Ga 0.5 In 0.5 P:Zn BSF layers in the GaAs third junction, respectively, and show a significantly improved concentrator device performance when Al 0.2 Ga 0.8 As:C is employed. Lastly, we demonstrate the importance of designing annealing tolerance into multijunction structures that are subjected to extended annealing during growth.},
doi = {10.1109/JPHOTOV.2018.2878317},
journal = {IEEE Journal of Photovoltaics},
number = 1,
volume = 9,
place = {United States},
year = {2018},
month = {11}
}

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