Transport Evidence for Sulfur Vacancies as the Origin of Unintentional n-Type Doping in Pyrite FeS 2

Bryan Voigt, William Moore, Michael A Manno, Jeff Walter, Jeff D. Jeremiason, Eray S. Aydil, Chris Leighton

Research output: Contribution to journalArticle

Abstract

Pyrite FeS 2 has long been considered a potential earth-abundant low-cost photovoltaic material for thin-film solar cells but has been plagued by low power conversion efficiencies and open-circuit voltages. Recent efforts have identified a lack of understanding and control of doping, as well as uncontrolled surface conduction, as key roadblocks to the development of pyrite photovoltaics. In particular, while n-type bulk behavior in unintentionally doped single crystals and thin films is speculated to arise from sulfur vacancies (V S ), proof remains elusive. Here, we provide strong evidence, from extensive electronic transport measurements on high-quality crystals, that V S are deep donors in bulk pyrite. Otherwise identical crystals grown via chemical vapor transport under varied S vapor pressures are thoroughly characterized structurally and chemically, and shown to exhibit systematically different electronic transport. Decreased S vapor pressure during growth leads to reduced bulk resistivity, increased bulk Hall electron density, reduced transport activation energy, onset of positive temperature coefficient of resistivity, and approach to an insulator-metal transition, all as would be expected from increased V S donor density. Impurity analyses show that these trends are uncorrelated with metal impurity concentration and that extracted donor densities significantly exceed total impurity concentrations, directly evidencing a native defect. Well-controlled, wide-range n-doping of pyrite is thus achieved via the control of V S concentration, with substantial implications for photovoltaic and other applications. The location of the V S state within the gap, the influence of specific impurities, unusual aspects to the insulator-metal transition, and the influence of doping on surface conduction are also discussed.

Original languageEnglish (US)
Pages (from-to)15552-15563
Number of pages12
JournalACS Applied Materials and Interfaces
Volume11
Issue number17
DOIs
StatePublished - May 1 2019

Fingerprint

Pyrites
Sulfur
Vacancies
Doping (additives)
Impurities
Metal insulator transition
Vapor pressure
Positive temperature coefficient
Crystals
Open circuit voltage
Conversion efficiency
Carrier concentration
Activation energy
Metals
Earth (planet)
Vapors
pyrite
Single crystals
Thin films
Defects

Keywords

  • crystal growth
  • defects
  • doping
  • electronic transport
  • insulator-metal transition
  • photovoltaic absorbers
  • semiconductors
  • solar cells
  • sulfur vacancies

How much support was provided by MRSEC?

  • Partial

Reporting period for MRSEC

  • Period 6

PubMed: MeSH publication types

  • Journal Article

Cite this

Transport Evidence for Sulfur Vacancies as the Origin of Unintentional n-Type Doping in Pyrite FeS 2. / Voigt, Bryan; Moore, William; Manno, Michael A; Walter, Jeff; Jeremiason, Jeff D.; Aydil, Eray S.; Leighton, Chris.

In: ACS Applied Materials and Interfaces, Vol. 11, No. 17, 01.05.2019, p. 15552-15563.

Research output: Contribution to journalArticle

@article{485d8c85cb5646b89a69d7976e9f6770,
title = "Transport Evidence for Sulfur Vacancies as the Origin of Unintentional n-Type Doping in Pyrite FeS 2",
abstract = "Pyrite FeS 2 has long been considered a potential earth-abundant low-cost photovoltaic material for thin-film solar cells but has been plagued by low power conversion efficiencies and open-circuit voltages. Recent efforts have identified a lack of understanding and control of doping, as well as uncontrolled surface conduction, as key roadblocks to the development of pyrite photovoltaics. In particular, while n-type bulk behavior in unintentionally doped single crystals and thin films is speculated to arise from sulfur vacancies (V S ), proof remains elusive. Here, we provide strong evidence, from extensive electronic transport measurements on high-quality crystals, that V S are deep donors in bulk pyrite. Otherwise identical crystals grown via chemical vapor transport under varied S vapor pressures are thoroughly characterized structurally and chemically, and shown to exhibit systematically different electronic transport. Decreased S vapor pressure during growth leads to reduced bulk resistivity, increased bulk Hall electron density, reduced transport activation energy, onset of positive temperature coefficient of resistivity, and approach to an insulator-metal transition, all as would be expected from increased V S donor density. Impurity analyses show that these trends are uncorrelated with metal impurity concentration and that extracted donor densities significantly exceed total impurity concentrations, directly evidencing a native defect. Well-controlled, wide-range n-doping of pyrite is thus achieved via the control of V S concentration, with substantial implications for photovoltaic and other applications. The location of the V S state within the gap, the influence of specific impurities, unusual aspects to the insulator-metal transition, and the influence of doping on surface conduction are also discussed.",
keywords = "crystal growth, defects, doping, electronic transport, insulator-metal transition, photovoltaic absorbers, semiconductors, solar cells, sulfur vacancies",
author = "Bryan Voigt and William Moore and Manno, {Michael A} and Jeff Walter and Jeremiason, {Jeff D.} and Aydil, {Eray S.} and Chris Leighton",
year = "2019",
month = "5",
day = "1",
doi = "10.1021/acsami.9b01335",
language = "English (US)",
volume = "11",
pages = "15552--15563",
journal = "ACS applied materials & interfaces",
issn = "1944-8244",
publisher = "American Chemical Society",
number = "17",

}

TY - JOUR

T1 - Transport Evidence for Sulfur Vacancies as the Origin of Unintentional n-Type Doping in Pyrite FeS 2

AU - Voigt, Bryan

AU - Moore, William

AU - Manno, Michael A

AU - Walter, Jeff

AU - Jeremiason, Jeff D.

AU - Aydil, Eray S.

AU - Leighton, Chris

PY - 2019/5/1

Y1 - 2019/5/1

N2 - Pyrite FeS 2 has long been considered a potential earth-abundant low-cost photovoltaic material for thin-film solar cells but has been plagued by low power conversion efficiencies and open-circuit voltages. Recent efforts have identified a lack of understanding and control of doping, as well as uncontrolled surface conduction, as key roadblocks to the development of pyrite photovoltaics. In particular, while n-type bulk behavior in unintentionally doped single crystals and thin films is speculated to arise from sulfur vacancies (V S ), proof remains elusive. Here, we provide strong evidence, from extensive electronic transport measurements on high-quality crystals, that V S are deep donors in bulk pyrite. Otherwise identical crystals grown via chemical vapor transport under varied S vapor pressures are thoroughly characterized structurally and chemically, and shown to exhibit systematically different electronic transport. Decreased S vapor pressure during growth leads to reduced bulk resistivity, increased bulk Hall electron density, reduced transport activation energy, onset of positive temperature coefficient of resistivity, and approach to an insulator-metal transition, all as would be expected from increased V S donor density. Impurity analyses show that these trends are uncorrelated with metal impurity concentration and that extracted donor densities significantly exceed total impurity concentrations, directly evidencing a native defect. Well-controlled, wide-range n-doping of pyrite is thus achieved via the control of V S concentration, with substantial implications for photovoltaic and other applications. The location of the V S state within the gap, the influence of specific impurities, unusual aspects to the insulator-metal transition, and the influence of doping on surface conduction are also discussed.

AB - Pyrite FeS 2 has long been considered a potential earth-abundant low-cost photovoltaic material for thin-film solar cells but has been plagued by low power conversion efficiencies and open-circuit voltages. Recent efforts have identified a lack of understanding and control of doping, as well as uncontrolled surface conduction, as key roadblocks to the development of pyrite photovoltaics. In particular, while n-type bulk behavior in unintentionally doped single crystals and thin films is speculated to arise from sulfur vacancies (V S ), proof remains elusive. Here, we provide strong evidence, from extensive electronic transport measurements on high-quality crystals, that V S are deep donors in bulk pyrite. Otherwise identical crystals grown via chemical vapor transport under varied S vapor pressures are thoroughly characterized structurally and chemically, and shown to exhibit systematically different electronic transport. Decreased S vapor pressure during growth leads to reduced bulk resistivity, increased bulk Hall electron density, reduced transport activation energy, onset of positive temperature coefficient of resistivity, and approach to an insulator-metal transition, all as would be expected from increased V S donor density. Impurity analyses show that these trends are uncorrelated with metal impurity concentration and that extracted donor densities significantly exceed total impurity concentrations, directly evidencing a native defect. Well-controlled, wide-range n-doping of pyrite is thus achieved via the control of V S concentration, with substantial implications for photovoltaic and other applications. The location of the V S state within the gap, the influence of specific impurities, unusual aspects to the insulator-metal transition, and the influence of doping on surface conduction are also discussed.

KW - crystal growth

KW - defects

KW - doping

KW - electronic transport

KW - insulator-metal transition

KW - photovoltaic absorbers

KW - semiconductors

KW - solar cells

KW - sulfur vacancies

UR - http://www.scopus.com/inward/record.url?scp=85065134544&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85065134544&partnerID=8YFLogxK

U2 - 10.1021/acsami.9b01335

DO - 10.1021/acsami.9b01335

M3 - Article

VL - 11

SP - 15552

EP - 15563

JO - ACS applied materials & interfaces

JF - ACS applied materials & interfaces

SN - 1944-8244

IS - 17

ER -