Oriented graphite layer formation in Ti/C and TiC/C multilayers deposited by high current pulsed cathodic arc

Persson, Per; Ryves, L.; Tucker, Mark; McKenzie, David R.; Bilek, M.M.M.

doi:10.1063/1.2959835

Cited by 9 publications

(11 citation statements)

References 31 publications

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“…The fi rst observation of note is that the pure-Cu kesterite is p-type whereas the pure-Ag material is n-type. This is consistent with theoretical predictions [ 18 ] as well as previous experiments. [ 19 ] Increasing the Ag/ (Ag + Cu) ratio decreases the hole density (Figure 4 a) of the kesterite material and simultaneously increases the mobility (Figure 4 b).…”

Section: Wileyonlinelibrarycomsupporting

confidence: 93%

“…Despite CZTSe containing a free hole concentration of ≈10 16 cm −3 , the Fermi level is consistently measured to be ≈0.4 eV from the valence edge. [ 14,16 ] This is in contrast to the position of 0.1 eV that is be predicted from classical semiconductor theory [ 23 ] (using effective masses of ≈0.3 and 0.08 [ 18 ] for holes and electrons, respectively, and a dielectric constant of 8.5 [ 19 ] ). This discrepancy has been associated with the extreme band tailing and compensation in CZTSSe.…”

Section: Wileyonlinelibrarycommentioning

confidence: 99%

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Photovoltaic Materials and Devices Based on the Alloyed Kesterite Absorber (Ag_xCu_1–_x)₂ZnSnSe₄

Gershon

Lee

Antunez

et al. 2016

Advanced Energy Materials

250

220

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narrows the CZTSSe band gap. The low energy barrier to Cu/Zn antisite formation is related to the similarity between the covalent radii of Cu and Zn. [ 4 ] The elevated processing temperatures (550-600 °C) needed to form large-grained CZTSSe fi lms (and peak device effi ciencies) provide the required thermal energy to randomize Cu and Zn in the unit cell, leading to a high density of antisite defects. [ 5 ] If disorder is the primary cause of performance loss in CZTSSe, then suppressing or eliminating it might offer a path to effi ciencies that compete with Cu(In,Ga)Se 2 (CIGS) technology.Ag is an interesting candidate for replacement of Cu since, in addition to belonging to the same chemical group as Cu, it possesses an atomic radius roughly 16% larger. This leads to the intriguing possibility that antisites can be suppressed by increasing the strain required to accommodate each defect (due to larger dissimilarity in radius). Ab initio calculations predict that substitution of Cu with Ag more than doubles the formation energy for antisites, which should result in an order of magnitude lower density of defects for equivalent processing. [ 6 ] Previous studies have examined the optical and crystallographic properties of the mixed Cu-Ag kesterite [ 7 ] and found that introducing 10% or 5% Ag into the CZTS(Se) layer gave 4.4% [ 8 ] or 7.1% [ 9 ] effi ciencies, respectively. These effi ciencies were shown to be an improvement over the baseline pure-Cu material; however, few direct measurements have been made to demonstrate how this substitution impacts the fundamental properties of the material.In this study, we have prepared thin fi lms of the mixed alloy (Ag x ,Cu 1x ) 2 ZnSnSe 4 (ACZTSe) across the full range of Ag/(Ag + Cu) ratios. We show, using Hall effect measurements, that while the pure-Cu kesterite compound is p-type, the carrier density decreases with increasing Ag content. For the highest values of Ag content (>50%), the material inverts to n-type. We also show, using femtosecond ultraviolet photoelectron spectroscopy (fs-UPS) measurements, that unlike in CZTSSe the Fermi level of AZTSe is not pinned near the center of the band gap, indicating that AZTSe does not suffer from the same degree of heavy compensation. Additionally, the energetic difference between the measured band gap and the photoluminescence (PL) peak position approaches zero for the pure-Ag compound. These results imply that the magnitude The photovoltaic absorber Cu 2 ZnSn(S x Se 1-x ) 4 (CZTSSe) has attracted interest in recent years due to the earth-abundance of its constituents and the realization of high performance (12.6% effi ciency). The open-circuit voltage in CZTSSe devices is believed to be limited by absorber band tailing caused by the exceptionally high density of Cu/Zn antisites. By replacing Cu in CZTSSe with Ag, whose covalent radius is ≈15% larger than that of Cu and Zn, the density of I-II antisite defects is predicted to drop. The fundamental properties of the mixed Ag-Cu kesterite compound are reported as a function of ...

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Section: Wileyonlinelibrarycomsupporting

confidence: 93%

Section: Wileyonlinelibrarycommentioning

confidence: 99%

Photovoltaic Materials and Devices Based on the Alloyed Kesterite Absorber (Ag_xCu_1–_x)₂ZnSnSe₄

Gershon

Lee

Antunez

et al. 2016

Advanced Energy Materials

250

220

View full text Add to dashboard Cite

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“…Table 1 taken for all crystals at T ¼ 220 C. ¼ 0.4 m 0 . Calculated effective hole mass for the top of the valence band exhibit strong anisotropy [9] and the range is consistent with values derived from our measurements. Crystals with elevated copper concentration, Cu/(Zn þ Sn) > 0.9, exhibit higher density of states, N V ¼ 3 Â 10 19 cm À3 and hole effective mass μ h Ã ¼ 0.9 m 0 .…”

Section: Resultssupporting

confidence: 88%

Majority Carrier Properties of Single Crystal Cu_2−xZnSnSe₄ with Varying Copper Composition

McCandless

Bishop

Lloyd

2019

Physica Status Solidi (b)

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The dependence of carrier concentration on copper content in Cu2−xZnSnSe4 single crystals, grown without fluxing agents, is presented over the composition range Cu/(Zn + Sn) of 0.77–0.93 and Zn/Sn from 1.3 (low Cu content) to 1.3 (high Cu content). Single phase mono‐crystals with facets up to 5 mm are synthesized from high‐purity elements and validated using Laue diffraction. A direct optical band gap of 0.98 eV is observed for a crystal with Cu/(Zn + Sn) = 0.85. Van der Pauw–Hall resistance analysis shows decreasing hole concentration, from 1019 cm−3 to 2 × 1015 cm−3, with decreasing copper content over the composition range. Hole mobility varies from 50 cm2 V−1 s−1 to 160 cm2 V−1 s−1, with no dependence on copper concentration. A linear temperature dependence of the Seebeck coefficient is found for all crystals. The Seebeck coefficient–carrier concentration dependence is used to determine the valence band density of states, NV, and corresponding effective mass, μh*. Crystals with Cu/(Zn + Sn) < 0.9 have NV = 4 × 1018 cm−3 and μh* = 0.4 m0 while crystals with elevated copper concentration, Cu/(Zn + Sn) > 0.9, exhibit higher density of states, NV = 3 × 1019 cm−3 and hole effective mass μh* = 0.9 m0. The increased valence band density of states at elevated copper composition is consistent with more Cu–Zn exchange sites contributing to bulk defects and band edge fluctuations. Temperature‐dependent conductivity measurements indicate a transition from metallic‐type to semiconductor‐type conduction at Cu/(Zn + Sn) < 0.9. At lower copper content, for a crystal with Cu/(Zn + Sn) = 0.83 and p = 1017 cm−3 the activation energy for intrinsic conduction is 60 meV. This behavior is attributed to the copper vacancy defect, VCu, and is comparable to reported values obtained in thin films and by first‐principles predictions.

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“…We start the discussion about the influence of absorber thickness on light absorption in CZTS TFSCs. There is a large spread in reported absorption coefficients in the literature [3,29,30], but an absorption coefficient of around 10 4 cm À1 above the absorption edge, increasing to 10 5 cm À1 for short wavelengths (above about 2.5 eV) is reasonable. This means, when comparing to Fig.…”

Section: Discussionmentioning

confidence: 97%

Influence of the Cu₂ZnSnS₄ absorber thickness on thin film solar cells

Ren

Scragg

Frisk

et al. 2015

Physica Status Solidi (a)

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In this study, we investigate the influence of absorber thickness on Cu 2 ZnSnS 4 (CZTS) solar cells, ranging from 500 to 2000 nm, with nearly constant metallic composition. Despite the observed ZnS and SnS phases on the surface and backside of all absorber films, scanning electron microscopy, Raman scattering, and X-ray diffraction show no large variations in material quality for the different thicknesses. The open-circuit voltage (V oc ), short-circuit current and overall power conversion efficiency of the fabricated devices show an initial improvement as the absorber thickness increases but saturate when the thickness exceeds 750 nm. External quantum efficiency (EQE) measurements suggest that the current is mainly limited by collection losses. This can result from nonoptimal bulk quality of the CZTS absorber (including the presence of secondary phases), which is apparently further reduced for the thinnest devices. The observed saturation of V oc agrees with the expected influence from strong interface recombination. Finally, an effective collection depth of 750-1000 nm for the minority carriers generated in the absorber can be estimated from EQE, indicating that the proper absorber thickness for our device process is approximately 1000 nm. Performance could be improved for thicker films, if the collection depth can be increased.

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Oriented graphite layer formation in Ti/C and TiC/C multilayers deposited by high current pulsed cathodic arc

Abstract: Articles you may be interested inPlasma-assisted atomic layer deposition of nanolaminates for gate dielectric applications

Cited by 9 publications

References 31 publications

Photovoltaic Materials and Devices Based on the Alloyed Kesterite Absorber (Ag_xCu_1–_x)₂ZnSnSe₄

Photovoltaic Materials and Devices Based on the Alloyed Kesterite Absorber (Ag_xCu_1–_x)₂ZnSnSe₄

Majority Carrier Properties of Single Crystal Cu_2−xZnSnSe₄ with Varying Copper Composition

Influence of the Cu₂ZnSnS₄ absorber thickness on thin film solar cells

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Oriented graphite layer formation in Ti/C and TiC/C multilayers deposited by high current pulsed cathodic arc

Abstract: Articles you may be interested inPlasma-assisted atomic layer deposition of nanolaminates for gate dielectric applications

Cited by 9 publications

References 31 publications

Photovoltaic Materials and Devices Based on the Alloyed Kesterite Absorber (AgxCu1–x)2ZnSnSe4

Photovoltaic Materials and Devices Based on the Alloyed Kesterite Absorber (AgxCu1–x)2ZnSnSe4

Majority Carrier Properties of Single Crystal Cu2−xZnSnSe4 with Varying Copper Composition

Influence of the Cu2ZnSnS4 absorber thickness on thin film solar cells

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Photovoltaic Materials and Devices Based on the Alloyed Kesterite Absorber (Ag_xCu_1–_x)₂ZnSnSe₄

Photovoltaic Materials and Devices Based on the Alloyed Kesterite Absorber (Ag_xCu_1–_x)₂ZnSnSe₄

Majority Carrier Properties of Single Crystal Cu_2−xZnSnSe₄ with Varying Copper Composition

Influence of the Cu₂ZnSnS₄ absorber thickness on thin film solar cells