Comparative operando XPS studies of quasi-Fermi level splitting and open-circuit voltage in CZTSe/CdS and CIGS/CdS junctions and device structures

Teeter, Glenn R.; Harvey, Steven P.; Perkins, Craig; Ramanathan, Kannan; Repins, Ingrid L.

doi:10.1116/1.5090345

Title: Comparative operando XPS studies of quasi-Fermi level splitting and open-circuit voltage in CZTSe/CdS and CIGS/CdS junctions and device structures

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Abstract

This contribution describes operando x-ray photoelectron spectroscopy (opXPS) studies of Cu(In,Ga)Se₂ (CIGS) and Cu₂ZnSnSe₄ (CZTSe) absorber layers and device structures. X-ray-excited valence-band and core-level spectra were acquired on bare absorber surfaces and after CdS and ZnO:Al depositions in standard absorber/CdS/ZnO/ZnO:Al device stacks. OpXPS data sets were acquired at various x-ray fluxes, with and without white-light illumination. From these measurements, quasi-Fermi level splitting (ΔE_F) values in the absorber/CdS junctions were measured directly as a function of excitation conditions. For both CIGS and CZTSe, results show that ..delta..EF proportional to the full open-circuit voltage (V_OC) of the completed devices is present after the deposition of the CdS layer - i.e., E_F = qV_OC - demonstrating that the so-called V_OC deficit in CZTSe solar cells is also present at this stage of processing. The authors find that photoexcitation due to x-rays or stray visible light during XPS or similar measurements can produce measurable photovoltages in materials, absorber/CdS junctions, and finished devices. In situ current density versus voltage measurements on a typical CIGS device reveal that x-ray-induced photoexcitation associated with typical XPS measurement conditions is equivalent to ~3 x 10^-3 suns, which in this study produced V_OC = 440 mV. These findings demonstrate thatmore »« less

Authors:

Teeter, Glenn R. ^[1];

^[1]; Perkins, Craig ^[1]; Ramanathan, Kannan ^[2]; Repins, Ingrid L. ^[1]

National Renewable Energy Lab. (NREL), Golden, CO (United States)
Stion Corporation, San Jose, CA (United States)

Publication Date:: Mon May 06 00:00:00 EDT 2019

Research Org.:: National Renewable Energy Lab. (NREL), Golden, CO (United States)

Sponsoring Org.:: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office

OSTI Identifier:: 1515765

Alternate Identifier(s):: OSTI ID: 1510830

Report Number(s):: NREL/JA-5K00-63930
Journal ID: ISSN 0734-2101

Grant/Contract Number:: AC36-08GO28308

Resource Type:: Accepted Manuscript

Journal Name:: Journal of Vacuum Science and Technology A

Additional Journal Information:: Journal Volume: 37; Journal Issue: 3; Journal ID: ISSN 0734-2101

Publisher:: American Vacuum Society

Country of Publication:: United States

Language:: English

Subject:: 36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; X-ray photoelectron spectroscopy; transition metal chalcogenides; electronic bandstructure; photoexcitations; electrical properties and parameters

Citation Formats


                    Teeter, Glenn R., Harvey, Steven P., Perkins, Craig, Ramanathan, Kannan, and Repins, Ingrid L. Comparative operando XPS studies of quasi-Fermi level splitting and open-circuit voltage in CZTSe/CdS and CIGS/CdS junctions and device structures.  United States: N. p., 2019. 
Web.  doi:10.1116/1.5090345.

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                    Teeter, Glenn R., Harvey, Steven P., Perkins, Craig, Ramanathan, Kannan, & Repins, Ingrid L. Comparative operando XPS studies of quasi-Fermi level splitting and open-circuit voltage in CZTSe/CdS and CIGS/CdS junctions and device structures.  United States.  https://doi.org/10.1116/1.5090345

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                    Teeter, Glenn R., Harvey, Steven P., Perkins, Craig, Ramanathan, Kannan, and Repins, Ingrid L. Mon .  
"Comparative operando XPS studies of quasi-Fermi level splitting and open-circuit voltage in CZTSe/CdS and CIGS/CdS junctions and device structures".  United States.  https://doi.org/10.1116/1.5090345.  https://www.osti.gov/servlets/purl/1515765.

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@article{osti_1515765,

  title        = {Comparative operando XPS studies of quasi-Fermi level splitting and open-circuit voltage in CZTSe/CdS and CIGS/CdS junctions and device structures},

  author       = {Teeter, Glenn R. and Harvey, Steven P. and Perkins, Craig and Ramanathan, Kannan and Repins, Ingrid L.},

  abstractNote = {This contribution describes operando x-ray photoelectron spectroscopy (opXPS) studies of Cu(In,Ga)Se2 (CIGS) and Cu2ZnSnSe4 (CZTSe) absorber layers and device structures. X-ray-excited valence-band and core-level spectra were acquired on bare absorber surfaces and after CdS and ZnO:Al depositions in standard absorber/CdS/ZnO/ZnO:Al device stacks. OpXPS data sets were acquired at various x-ray fluxes, with and without white-light illumination. From these measurements, quasi-Fermi level splitting (ΔEF) values in the absorber/CdS junctions were measured directly as a function of excitation conditions. For both CIGS and CZTSe, results show that ..delta..EF proportional to the full open-circuit voltage (VOC) of the completed devices is present after the deposition of the CdS layer - i.e., EF = qVOC - demonstrating that the so-called VOC deficit in CZTSe solar cells is also present at this stage of processing. The authors find that photoexcitation due to x-rays or stray visible light during XPS or similar measurements can produce measurable photovoltages in materials, absorber/CdS junctions, and finished devices. In situ current density versus voltage measurements on a typical CIGS device reveal that x-ray-induced photoexcitation associated with typical XPS measurement conditions is equivalent to ~3 x 10-3 suns, which in this study produced VOC = 440 mV. These findings demonstrate that accounting for photoexcitation conditions during XPS or similar measurements can improve band-offset determinations and produce more reliable values for the junction built-in voltage. The implications of the study findings on the CZTSe VOC deficit and device performance are discussed.},

  doi          = {10.1116/1.5090345},

  journal      = {Journal of Vacuum Science and Technology A},

  number       = 3,

  volume       = 37,

  place        = {United States},

  year         = {Mon May 06 00:00:00 EDT 2019},

  month        = {Mon May 06 00:00:00 EDT 2019}

}

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