The competing roles of i-ZnO in Cu(ln,Ga)Se¬2 solar cells

B.L. Williams, V. Zardetto, B.J. Kniknie, M.A. Verheijen, W.M.M. Kessels, M. Creatore

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The electrical role of the highly resistive and transparent (HRT) i-ZnO layer in Cu(In, Ga)Se2(CIGS) solar cells is investigated. By tuning the resistivity of atomic layer deposited (ALD) i-ZnO through the use of post-growth O2-plasma treatments, it is shown that low i-ZnO carrier densities (i.e. high resistivities) actually restrict the performance of CIGS solar cells by reducing the extent of band-bending of the CdS/CIGS junction (the effect of series resistance is ruled out as the origin of any observed differences). This is the first evidence that i-ZnO has a negative electrical effect in CIGS solar cells (alongside the positive effect of shunt mitigation), and based on these results, attempts to maximise resistivity of the i-ZnO (typically sought-after for this HRT layer) are not recommended. Device efficiencies of 12.5% were obtained when using low resistivity as-grown ALD i-ZnO (resistivity, ρ=0.6 Ω cm, carrier density, n=3.5·1018 cm−3, and work function, Φ=4.06 eV), but this decreased to 11.5% when using high resistivity, plasma-treated ALD i-ZnO (ρ=134 Ω cm, n=0.2·1018 cm−3, and Φ=4.21 eV). SCAPS modelling revealed the reason for the difference to be the effect that the i-ZnO work function (controlled by carrier density) has on the band-bending and built-in voltage, Vbi, of the main junction. Capacitance-voltage experiments confirmed that the Vbi is lower (∆Vbi~0.1 V) when using low carrier density, high resistivity i-ZnO. This general effect was also found when using RF-sputtered i-ZnO, whereby the inclusion of high resistivity i-ZnO similarly generated lower efficiencies (15.0%) than low resistivity i-ZnO (15.9%).
Originele taal-2Engels
Pagina's (van-tot)798-807
TijdschriftSolar Energy Materials and Solar Cells
Volume157
Nummer van het tijdschriftDecember 2016
DOI's
StatusGepubliceerd - 2016

Vingerafdruk

Carrier concentration
Solar cells
Plasmas
Electric potential
Capacitance
Tuning
Experiments

Citeer dit

Williams, B.L. ; Zardetto, V. ; Kniknie, B.J. ; Verheijen, M.A. ; Kessels, W.M.M. ; Creatore, M. / The competing roles of i-ZnO in Cu(ln,Ga)Se¬2 solar cells. In: Solar Energy Materials and Solar Cells. 2016 ; Vol. 157, Nr. December 2016. blz. 798-807.
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title = "The competing roles of i-ZnO in Cu(ln,Ga)Se¬2 solar cells",
abstract = "The electrical role of the highly resistive and transparent (HRT) i-ZnO layer in Cu(In, Ga)Se2(CIGS) solar cells is investigated. By tuning the resistivity of atomic layer deposited (ALD) i-ZnO through the use of post-growth O2-plasma treatments, it is shown that low i-ZnO carrier densities (i.e. high resistivities) actually restrict the performance of CIGS solar cells by reducing the extent of band-bending of the CdS/CIGS junction (the effect of series resistance is ruled out as the origin of any observed differences). This is the first evidence that i-ZnO has a negative electrical effect in CIGS solar cells (alongside the positive effect of shunt mitigation), and based on these results, attempts to maximise resistivity of the i-ZnO (typically sought-after for this HRT layer) are not recommended. Device efficiencies of 12.5{\%} were obtained when using low resistivity as-grown ALD i-ZnO (resistivity, ρ=0.6 Ω cm, carrier density, n=3.5·1018 cm−3, and work function, Φ=4.06 eV), but this decreased to 11.5{\%} when using high resistivity, plasma-treated ALD i-ZnO (ρ=134 Ω cm, n=0.2·1018 cm−3, and Φ=4.21 eV). SCAPS modelling revealed the reason for the difference to be the effect that the i-ZnO work function (controlled by carrier density) has on the band-bending and built-in voltage, Vbi, of the main junction. Capacitance-voltage experiments confirmed that the Vbi is lower (∆Vbi~0.1 V) when using low carrier density, high resistivity i-ZnO. This general effect was also found when using RF-sputtered i-ZnO, whereby the inclusion of high resistivity i-ZnO similarly generated lower efficiencies (15.0{\%}) than low resistivity i-ZnO (15.9{\%}).",
author = "B.L. Williams and V. Zardetto and B.J. Kniknie and M.A. Verheijen and W.M.M. Kessels and M. Creatore",
year = "2016",
doi = "10.1016/j.solmat.2016.07.049",
language = "English",
volume = "157",
pages = "798--807",
journal = "Solar Energy Materials and Solar Cells",
issn = "0927-0248",
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The competing roles of i-ZnO in Cu(ln,Ga)Se¬2 solar cells. / Williams, B.L.; Zardetto, V.; Kniknie, B.J.; Verheijen, M.A.; Kessels, W.M.M.; Creatore, M.

In: Solar Energy Materials and Solar Cells, Vol. 157, Nr. December 2016, 2016, blz. 798-807.

Onderzoeksoutput: Bijdrage aan tijdschriftTijdschriftartikelAcademicpeer review

TY - JOUR

T1 - The competing roles of i-ZnO in Cu(ln,Ga)Se¬2 solar cells

AU - Williams, B.L.

AU - Zardetto, V.

AU - Kniknie, B.J.

AU - Verheijen, M.A.

AU - Kessels, W.M.M.

AU - Creatore, M.

PY - 2016

Y1 - 2016

N2 - The electrical role of the highly resistive and transparent (HRT) i-ZnO layer in Cu(In, Ga)Se2(CIGS) solar cells is investigated. By tuning the resistivity of atomic layer deposited (ALD) i-ZnO through the use of post-growth O2-plasma treatments, it is shown that low i-ZnO carrier densities (i.e. high resistivities) actually restrict the performance of CIGS solar cells by reducing the extent of band-bending of the CdS/CIGS junction (the effect of series resistance is ruled out as the origin of any observed differences). This is the first evidence that i-ZnO has a negative electrical effect in CIGS solar cells (alongside the positive effect of shunt mitigation), and based on these results, attempts to maximise resistivity of the i-ZnO (typically sought-after for this HRT layer) are not recommended. Device efficiencies of 12.5% were obtained when using low resistivity as-grown ALD i-ZnO (resistivity, ρ=0.6 Ω cm, carrier density, n=3.5·1018 cm−3, and work function, Φ=4.06 eV), but this decreased to 11.5% when using high resistivity, plasma-treated ALD i-ZnO (ρ=134 Ω cm, n=0.2·1018 cm−3, and Φ=4.21 eV). SCAPS modelling revealed the reason for the difference to be the effect that the i-ZnO work function (controlled by carrier density) has on the band-bending and built-in voltage, Vbi, of the main junction. Capacitance-voltage experiments confirmed that the Vbi is lower (∆Vbi~0.1 V) when using low carrier density, high resistivity i-ZnO. This general effect was also found when using RF-sputtered i-ZnO, whereby the inclusion of high resistivity i-ZnO similarly generated lower efficiencies (15.0%) than low resistivity i-ZnO (15.9%).

AB - The electrical role of the highly resistive and transparent (HRT) i-ZnO layer in Cu(In, Ga)Se2(CIGS) solar cells is investigated. By tuning the resistivity of atomic layer deposited (ALD) i-ZnO through the use of post-growth O2-plasma treatments, it is shown that low i-ZnO carrier densities (i.e. high resistivities) actually restrict the performance of CIGS solar cells by reducing the extent of band-bending of the CdS/CIGS junction (the effect of series resistance is ruled out as the origin of any observed differences). This is the first evidence that i-ZnO has a negative electrical effect in CIGS solar cells (alongside the positive effect of shunt mitigation), and based on these results, attempts to maximise resistivity of the i-ZnO (typically sought-after for this HRT layer) are not recommended. Device efficiencies of 12.5% were obtained when using low resistivity as-grown ALD i-ZnO (resistivity, ρ=0.6 Ω cm, carrier density, n=3.5·1018 cm−3, and work function, Φ=4.06 eV), but this decreased to 11.5% when using high resistivity, plasma-treated ALD i-ZnO (ρ=134 Ω cm, n=0.2·1018 cm−3, and Φ=4.21 eV). SCAPS modelling revealed the reason for the difference to be the effect that the i-ZnO work function (controlled by carrier density) has on the band-bending and built-in voltage, Vbi, of the main junction. Capacitance-voltage experiments confirmed that the Vbi is lower (∆Vbi~0.1 V) when using low carrier density, high resistivity i-ZnO. This general effect was also found when using RF-sputtered i-ZnO, whereby the inclusion of high resistivity i-ZnO similarly generated lower efficiencies (15.0%) than low resistivity i-ZnO (15.9%).

U2 - 10.1016/j.solmat.2016.07.049

DO - 10.1016/j.solmat.2016.07.049

M3 - Article

VL - 157

SP - 798

EP - 807

JO - Solar Energy Materials and Solar Cells

JF - Solar Energy Materials and Solar Cells

SN - 0927-0248

IS - December 2016

ER -