Back-surface recombination, electron reflectors, and paths to 28% efficiency for thin-film photovoltaics: A CdTe case study

doi:10.1063/1.5063799

This content will become publicly available on February 1, 2020

Title: Back-surface recombination, electron reflectors, and paths to 28% efficiency for thin-film photovoltaics: A CdTe case study

As thin-film and silicon solar technologies mature, questions emerge about the upper bounds of thin-film solar performance and realistic experimental paths to reach them. Directions include increasing absorber hole density and bulk lifetime, improving the junction interface, reducing back-surface recombination, and implementing a back-surface electron reflector. Textbook solutions of idealized p-n junctions create a powerful conceptualization of solar cells as predominantly minority-carrier-driven devices. We demonstrate that thin films are distinct, and models often fail to capture the important role of majority-carrier lifetime, leading to contradictions with lifetime measurements and overestimates of potential device improvement from back-surface passivation and/or reflectors. Furthermore, we identify methods to probe majority-carrier lifetime and re-examine the degree to which back-surface passivation and electron reflectors can increase efficiency for a range of common thin-film interface and absorber properties, using current and emerging CdTe technology as an example. Here, the results indicate that a practical approach is to focus first on improving front-interface recombination velocity and the absorber properties, and then on implementing the back-surface passivation or reflector, which can ultimately allow thin-film solar technology to reach 28% efficiency.

Authors:

Duenow, Joel N. ^[1] ; Metzger, Wyatt K. ^[1]

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

Publication Date:: 2019-02-01

Report Number(s):: NREL/JA-5K00-73045
Journal ID: ISSN 0021-8979

Grant/Contract Number:: AC36-08GO28308

Type:: Accepted Manuscript

Journal Name:: Journal of Applied Physics

Additional Journal Information:: Journal Volume: 125; Journal Issue: 5; Journal ID: ISSN 0021-8979

Publisher:: American Institute of Physics (AIP)

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)

Country of Publication:: United States

Language:: English

Subject:: 14 SOLAR ENERGY; 36 MATERIALS SCIENCE; CdTe; lifetime; back surface recombination; electron reflector

OSTI Identifier:: 1494117


                    Duenow, Joel N., and Metzger, Wyatt K.. Back-surface recombination, electron reflectors, and paths to 28% efficiency for thin-film photovoltaics: A CdTe case study.  United States: N. p.,  
        Web.  doi:10.1063/1.5063799.

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                    Duenow, Joel N., & Metzger, Wyatt K.. Back-surface recombination, electron reflectors, and paths to 28% efficiency for thin-film photovoltaics: A CdTe case study.  United States.  doi:10.1063/1.5063799.

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                    Duenow, Joel N., and Metzger, Wyatt K.. 2019.  
        "Back-surface recombination, electron reflectors, and paths to 28% efficiency for thin-film photovoltaics: A CdTe case study".  United States.  
        doi:10.1063/1.5063799.

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@article{osti_1494117,

  title        = {Back-surface recombination, electron reflectors, and paths to 28% efficiency for thin-film photovoltaics: A CdTe case study},

  author       = {Duenow, Joel N. and Metzger, Wyatt K.},

  abstractNote = {As thin-film and silicon solar technologies mature, questions emerge about the upper bounds of thin-film solar performance and realistic experimental paths to reach them. Directions include increasing absorber hole density and bulk lifetime, improving the junction interface, reducing back-surface recombination, and implementing a back-surface electron reflector. Textbook solutions of idealized p-n junctions create a powerful conceptualization of solar cells as predominantly minority-carrier-driven devices. We demonstrate that thin films are distinct, and models often fail to capture the important role of majority-carrier lifetime, leading to contradictions with lifetime measurements and overestimates of potential device improvement from back-surface passivation and/or reflectors. Furthermore, we identify methods to probe majority-carrier lifetime and re-examine the degree to which back-surface passivation and electron reflectors can increase efficiency for a range of common thin-film interface and absorber properties, using current and emerging CdTe technology as an example. Here, the results indicate that a practical approach is to focus first on improving front-interface recombination velocity and the absorber properties, and then on implementing the back-surface passivation or reflector, which can ultimately allow thin-film solar technology to reach 28% efficiency.},

  doi          = {10.1063/1.5063799},

  journal      = {Journal of Applied Physics},

  number       = 5,

  volume       = 125,

  place        = {United States},

  year         = {2019},

  month        = {2}

}

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Free Publicly Accessible Full Text
This content will become publicly available on February 1, 2020
Publisher's Version of Record
10.1063/1.5063799
https://doi.org/10.1063/1.5063799

Works referenced in this record:

Strategies to increase CdTe solar-cell voltage
journal, May 2007

Sites, James; Pan, Jun
Thin Solid Films, Vol. 515, Issue 15, p. 6099-6102
DOI: 10.1016/j.tsf.2006.12.147

Time-resolved photoluminescence studies of CdTe solar cells
journal, September 2003

Metzger, W. K.; Albin, D.; Levi, D.
Journal of Applied Physics, Vol. 94, Issue 5, p. 3549-3555
DOI: 10.1063/1.1597974

Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber
journal, October 2013

Stranks, S. D.; Eperon, G. E.; Grancini, G.
Science, Vol. 342, Issue 6156, p. 341-344
DOI: 10.1126/science.1243982

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Title: Back-surface recombination, electron reflectors, and paths to 28% efficiency for thin-film photovoltaics: A CdTe case study

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