Formation of Cu(In,Ga)S2 chalcopyrite thin films following a 3-stage co-evaporation process

Thomere, Angélica; Barreau, Nicolas; Stéphant, Nicolas; Guillot‐Deudon, Catherine; Gautron, Éric; Caldés, Maria Teresa; Lafond, A.

doi:10.1016/j.solmat.2021.111563

Cited by 12 publications

(11 citation statements)

References 21 publications

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“…Indeed, three-stage coevaporation has been recently demonstrated to yield devices with 14-15.5% efficiency [9], [85]. At the same time, Thomere et al described an unexpected bilayer morphology of the absorbers stemming from segregation of spinel CuIn5S8-like and Cu-poor tetragonal Cu(In,Ga)S2 phases during the second deposition stage [86]. The root cause of this behaviour is the narrow single-phase region of CH-CIS, which is further complicated by the introduction of gallium.…”

Section: Discussionmentioning

confidence: 99%

Experimental and Theoretical Study of Stable and Metastable Phases in Sputtered CuInS₂

et al. 2022

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The chalcopyrite Cu(In,Ga)S2 has gained renewed interest in recent years due to the potential application in tandem solar cells. In this contribution, a combined theoretical and experimental approach is applied to investigate stable and metastable phases forming in CuInS2 (CIS) thin films. Ab initio calculations are performed to obtain formation energies, Xray diffraction patterns, and Raman spectra of CIS polytypes and related compounds. Multiple CIS structures with zinc-blende and wurtzite-derived lattices are identified and their XRD/Raman patterns are shown to contain overlapping features, which could lead to misidentification. Thin films with compositions from Cu-rich to Cu-poor are synthesized with a two-step approach based on sputtering from binary targets followed by high-temperature sulfurization. It is discovered that several CIS polymorphs are formed when growing the material with this approach. In the Cu-poor material, wurtzite CIS is observed for the first time in sputtered thin films along with chalcopyrite CIS and CuAu-ordered CIS. Once the wurtzite CIS phase has formed, it is difficult to convert into the stable chalcopyrite polymorph. CuIn5S8 and NaInS2 accommodating In-excess are found alongside the CIS polymorphs. It is argued that the metastable polymorphs are stabilized by off-stoichiometry of the precursors, hence tight composition control is required.

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Section: Discussionmentioning

confidence: 99%

Experimental and Theoretical Study of Stable and Metastable Phases in Sputtered CuInS₂

et al. 2022

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“…[ 117,118 ] As discussed in Section 4.3, the control of the Ga gradient might be more difficult in sulfides, because of its phase diagram (Figure 8). [ 91 ] However, the positive effect of Ga addition, obvious in Figure 7, could also be due to the larger existence region of Cu‐poor Cu(In,Ga)S 2 with higher Ga, as discussed earlier (Figure 8). With the currently available data, it is clear that the addition of Ga improves the absorber quality, but the exact reason cannot be discerned, yet.…”

Section: Comparison Of Loss Mechanisms In Solar Cellsmentioning

confidence: 73%

“…Interestingly, the phase segregation does not occur in a homogeneous distribution of small grains but as a layered structure. [ 91 ] Segregation into Ga‐rich and In‐rich phases is, however, not limited to three‐stage coevaporation processes, it was also observed in sequential processes that start with a metallic precursor, even in Cu‐rich films. [ 92 ] The segregation leads to layers inside the absorber with a low Ga content and thus a low bandgap.…”

Section: Cu‐rich Versus Cu‐poormentioning

confidence: 99%

“…Since the absorption edge depends on the lowest bandgap, this segregation is detrimental for high open‐circuit voltages and for high bandgaps. [ 91 ] It appears, that overall lower Ga contents, leading to an absorption edge up to about 1.7 eV, and higher temperatures allow a better control of the Ga profile throughout the absorber depth. [ 18,19,21 ]…”

Section: Cu‐rich Versus Cu‐poormentioning

confidence: 99%

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Sulfide Chalcopyrite Solar Cells––Are They the Same as Selenides with a Wider Bandgap?

Siebentritt

Lomuscio

Adeleye

et al. 2022

Physica Rapid Research Ltrs

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Sulfide chalcopyrite solar cells are receiving renewed interest since they have reached a certified efficiency above 15%. Due to their wider bandgap, they are interesting candidates for top cells in tandem applications. They share many properties with the much deeper studied selenide chalcopyrites, but also some important differences. While the structure of shallow and deep defects appears very similar, the phase diagram is different with a much smaller existence range of Cu‐poor CuInS2. The problematic character of the surface of material grown under Cu excess is present in both sulfides and selenides. Both materials show increased tail states when grown Cu‐poor. To achieve sufficient bulk quality of sulfide absorbers, higher growth temperatures and a higher supply of sodium appear to be necessary.

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“…So far, the co-evaporation process leading to the best performance is the sequential 3-stage process. However, as recently reported [6,11] its implementation can result in the formation of bi-layered films corresponding to two different indium and gallium contents. In fact, a major part of the gallium is found at the half-rear part of the film (i.e.…”

Section: Introductionmentioning

confidence: 82%

Investigation of co-evaporated polycrystalline Cu(In,Ga)S₂thin film yielding 16.0 % efficiency solar cell

et al. 2022

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The interest for pure sulfide Cu(In,Ga)S2 chalcopyrite thin films is increasing again because their optical properties make them relevant candidates to be applied as top cell absorbers in tandem structures. Nonetheless, their use as so is still hindered by the level of single-junction cells performance achieved so far, which are far below those demonstrated by selenide absorbers. Amongst the reasons at the origin of the limited efficiency of Cu(In,Ga)S2-based solar devices, one can mention the poor tolerance of S-chalcopyrite to Cu deficiency. In fact, Cu-poor Cu(In,Ga)S2 films contain CuIn5S8 thiospinel secondary phase which is harmful for device performance. In the present work, we investigate Cu(In,Ga)S2 thin films grown by a modified three-stage process making use of graded indium and gallium fluxes during the first stage. The resulting absorbers are single phase and made of large grains extended throughout the entire film thickness. We propose that such a morphology is a proof of the recrystallization of the entire film during the synthesis. Devices prepared from those films and buffered with bath deposited CdS demonstrate outstanding efficiency of 16.0%. Replacing CdS by Zn(O,S) buffer layer leads to increased open circuit voltage and short circuit current; however, performance become limited by lowered fill factor.

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Formation of Cu(In,Ga)S2 chalcopyrite thin films following a 3-stage co-evaporation process

Cited by 12 publications

References 21 publications

Experimental and Theoretical Study of Stable and Metastable Phases in Sputtered CuInS₂

Experimental and Theoretical Study of Stable and Metastable Phases in Sputtered CuInS₂

Sulfide Chalcopyrite Solar Cells––Are They the Same as Selenides with a Wider Bandgap?

Investigation of co-evaporated polycrystalline Cu(In,Ga)S₂thin film yielding 16.0 % efficiency solar cell

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Formation of Cu(In,Ga)S2 chalcopyrite thin films following a 3-stage co-evaporation process

Cited by 12 publications

References 21 publications

Experimental and Theoretical Study of Stable and Metastable Phases in Sputtered CuInS2

Experimental and Theoretical Study of Stable and Metastable Phases in Sputtered CuInS2

Sulfide Chalcopyrite Solar Cells––Are They the Same as Selenides with a Wider Bandgap?

Investigation of co-evaporated polycrystalline Cu(In,Ga)S2thin film yielding 16.0 % efficiency solar cell

Contact Info

Product

Resources

About

Experimental and Theoretical Study of Stable and Metastable Phases in Sputtered CuInS₂

Experimental and Theoretical Study of Stable and Metastable Phases in Sputtered CuInS₂

Investigation of co-evaporated polycrystalline Cu(In,Ga)S₂thin film yielding 16.0 % efficiency solar cell