Inert gas cluster formation in sputter-deposited thin film CdTe solar cells

Hatton, P. D.; Goddard, Pooja; Smith, Roger; Abbas, Ali; Potamialis, Christos; Greenhalgh, Rachael; Walls, John M.

doi:10.1016/j.tsf.2019.137614

Cited by 6 publications

(6 citation statements)

References 12 publications

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“…This is due to a low barrier of 0.2 eV for a di-interstitial to form providing two Ar/Xe atoms are in adjacent interstitial sites. The elevated reverse barrier of 0.9 eV for the dissipation of the di-interstitial also contributes to the large number of these defects [34]. Moreover, energy barriers and pathways for di-interstitial Ar diffusion were also determined.…”

Section: Resultsmentioning

confidence: 99%

“…If sputter-deposited thin films of CdTe are to be used for solar applications, it is essential that the inclusion of inert gas is minimized since it leads to the formation of voids and surface blistering. In addition, it has also been observed that delamination at the CdTe/CdS interface can occur due to large-scale agglommeration there of the inert gas [34].…”

Section: Discussionmentioning

confidence: 99%

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Inert gas bubble formation in magnetron sputtered thin-film CdTe solar cells

et al. 2020

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Cadmium telluride (CdTe) solar cells are deposited in current production using evaporation-based tech- niques. Fabricating CdTe solar cells using magnetron sputtering would have the advantage of being more cost-efficient. Here, we show that such deposition results in the incorporation of the magnetron working gas Ar, within the films. Post deposition processing with CdCl 2 improves cell efficiency and during which stacking faults are removed. The Ar then accumulates into clusters leading to the creation of voids and blisters on the surface. Using molecular dynamics, the penetration threshold energies are determined for both Ar and Xe, with CdTe in both zinc-blende and wurtzite phases. These calculations show that more Ar than Xe can penetrate into the growing film with most penetration across the (111) surface. The mechanisms and energy barriers for interstitial Ar and Xe diffusion in zinc-blende are determined. Barriers are reduced near existing clusters, increasing the probability of capture-based cluster growth. Barriers in wurtzite are higher with non-Arrhenius behaviour observed. This provides an explanation for the increase in the size of voids observed after stacking fault removal. Blister exfoliation was also modelled, showing the formation of shallow craters with a raised rim.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Inert gas bubble formation in magnetron sputtered thin-film CdTe solar cells

et al. 2020

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“…However, due to the low barriers, arsenic can be expected to conduct this motion ≃300 times before a 'down' transition in the neutral charge state, again calculated at 1100 K with Arrhenius' equation and assuming comparable prefactors between the two mechanisms. Therefore, wurtzite structured layers in CdTe could allow for fast migration of As atoms 'across' the (111) plane, in stark contrast to previous work for inert gas diffusion [18,28].…”

Section: Arsenic Stable Sites and Diffusion In Bulk Cdtementioning

confidence: 89%

“…Migrating interstitials in CdTe have previously been shown to cluster, inhibiting their diffusivity even with small cluster of two atoms [28]. An arsenic di-interstitial in an otherwise clean CdTe structure forms a tri-interstitial with Te, seen in figure 2(a).…”

Section: Arsenic Stable Sites and Diffusion In Bulk Cdtementioning

confidence: 99%

Arsenic doping and diffusion in CdTe: a DFT study of bulk and grain boundaries

Hatton

Watts

Zhou

et al. 2022

J. Phys.: Condens. Matter

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The doping of CdTe with As is a method which is thought to increase cell eﬃciency by increasing electron hole concentrations. This doping relies on the diﬀusion of As through CdTe resulting in AsTe substitution. The potential eﬀectiveness of this is considered through kinetic and electronic properties calculations in both bulk and Σ3 and Σ9 grain boundaries using Density Functional Theory. In bulk zinc-blende CdTe, isolated As diﬀuses with barriers < 0.5 eV and with similar barriers through wurtzite structured CdTe, generated by stacking faults, suggesting that As will not be trapped at the stacking faults and hence the transport of isolated As will be unhindered in bulk CdTe. Substitutional arsenic in bulk CdTe has little eﬀect on the band gap except when it is positively charged in the AX-centre position or occurring as a di-interstitial. However in contrast to the case of chlorine, arsenic present in the grain boundaries introduces defect states into the band gap. This suggests that a doping strategy whereby the grain boundaries are ﬁrst saturated with chlorine, before single arsenic atoms are introduced, might be more beneﬁcial.

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“…Examples of blistering during annealing of single layers deposited by such technique are described in [7][8][9]. One recent and detailed study is that of Hatton et al [10] on Ar and Xe clustering in cadmium telluride deposited by pulsed MS, where blisters appear during an activation annealing at 400 • C. In such a case, the question arises whether blistering is initiated by stress-induced cracking, or gas accumulation, or a synergistic combination of both.…”

Section: Introductionmentioning

confidence: 99%

Ar transport and blister growth kinetics in titania-doped germania-based optical coatings

Lalande,

Davenport,

Marchand

et al. 2024

Class. Quantum Grav.

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Blistering is a phenomenon sometimes observed in sputtered-deposited thin films but seldom investigated in detail. Here, we consider the case of titania-doped germania (TGO)/silica multi-layers deposited by ion beam sputtering. TGO is a candidate as high refractive index material in the Bragg mirrors for the next iteration of gravitational waves detectors. It needs to be annealed at 600°C for 100h in order to reach the desired relaxation state. However under some growth conditions, in 52-layer TGO/silica stacks, blistering occurs upon annealing at a temperature near 500°C, which corresponds to the temperature where Ar desorbs from TGO. In order to better understand the blistering phenomenon, we measure the Ar transport in single layers of TGO and silica. In the case of <1 μm-thick TGO layers, the Ar desorption is mainly limited by detrapping. The transport model also correctly predicts the evolution of the total amount of Ar in a 8.5 μm stack of TGO and silica layers annealed at 450°C, but in that case, the process is mainly limited by diffusion. Since Ar diffusion is an order of magnitude slower in TGO compared to silica, we observe a correspondingly strong accumulation of Ar in TGO. The Ar transport model is used to explain some regimes of the blisters growth, and we find indications that Ar accumulation is a driver for their growth in general, but the blisters nucleation remains a complex phenomenon influenced by several other factors including stress, substrate roughness, and impurities.

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Inert gas cluster formation in sputter-deposited thin film CdTe solar cells

Cited by 6 publications

References 12 publications

Inert gas bubble formation in magnetron sputtered thin-film CdTe solar cells

Inert gas bubble formation in magnetron sputtered thin-film CdTe solar cells

Arsenic doping and diffusion in CdTe: a DFT study of bulk and grain boundaries

Ar transport and blister growth kinetics in titania-doped germania-based optical coatings

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