Energy level alignment of 
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 absorber compounds with 
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Ghorbani, Elaheh; Erhart, Paul; Albe, Karsten

doi:10.1103/physrevmaterials.3.075401

Cited by 20 publications

(8 citation statements)

References 56 publications

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“…In contrast, Karthikeyan et al reported an opposite trend as found for their In x S y deposited by pulsed direct magnetron sputtering [23]. From theoretical density calculations there is only a very small difference between direct and indirect transitions in β-In 2 S 3 [29,30].…”

Section: Discussionmentioning

confidence: 87%

Influence of Substrate Temperature during InxSy Sputtering on Cu(In,Ga)Se2/Buffer Interface Properties and Solar Cell Performance

et al. 2020

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Indium sulfide (InxSy)—besides CdS and Zn(O,S)—is already used as a buffer layer in chalcopyrite-type thin-film solar cells and modules. We discuss the influence of the substrate temperature during very fast magnetron sputtering of InxSy buffer layers on the interface formation and the performance of Cu(In,Ga)Se2 solar cells. The substrate temperature was increased from room temperature up to 240 °C, and the highest power conversion efficiencies were obtained at a temperature plateau around 200 °C, with the best values around 15.3%. Industrially relevant in-line co-evaporated polycrystalline Cu(In,Ga)Se2 absorber layers were used, which yield solar cell efficiencies of up to 17.1% in combination with a solution-grown CdS buffer. The chemical composition of the InxSy buffer as well as of the Cu(In,Ga)Se2/InxSy interface was analyzed by time-of-flight secondary ion mass spectrometry. Changes from homogenous and stoichiometric In2S3 layers deposited at RT to inhomogenous and more sulfur-rich and indium-deficient compositions for higher temperatures were observed. This finding is accompanied with a pronounced copper depletion at the Cu(In,Ga)Se2 absorber surface, and a sodium accumulation in the InxSy buffer and at the absorber/buffer interface. These last two features seem to be the origin for achieving the highest conversion efficiencies at substrate temperatures around 200 °C.

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Section: Discussionmentioning

confidence: 87%

Influence of Substrate Temperature during InxSy Sputtering on Cu(In,Ga)Se2/Buffer Interface Properties and Solar Cell Performance

et al. 2020

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“…For instance, the VBM of ZnSe is 0.52 eV higher than that of ZnS [30]. In CBCs, similar to chalcopyrites [31] and Kesterites [32], the valence band offset between selenides and sulfides is small. This feature is attributed to existence of p−d repulsion in these materials.…”

Section: Resultsmentioning

confidence: 98%

On efficiency of earth-abundant chalcogenide photovoltaic materials buffered with CdS: the limiting effect of band alignment

Ghorbani

2020

J. Phys. Energy

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Earth-abundant and environmentally-friendly Cu 2 -II-IV-VI 4 (II=Sr, Ba; IV=Ge, Sn; VI=S,Se) are considered materials for the absorber layers in thin film solar cells. Attempts to understand and improve optoelectronic properties of these newly emerged absorbers resulted in an efficiency of 5.2% in less than two years. However, the energy band alignment at the buffer/absorber interface has not been studied yet; an information which is of crucial importance for designing high performance devices. Therefore, current study focuses on the band offsets between these materials and the CdS buffer. Using first-principles calculations, band discontinuities are calculated at the buffer/absorber interface. The results yield a type-II band alignment between all Cu 2 -II-IV-VI 4 absorbers and CdS, hence a negative DE c . Adoption of a negative DE c (cliff-like conduction band offset) at the buffer/ absorber interface, however, gives rise to low open circuit voltage and high interface-related recombinations. Therefore, it is necessary to search for an alternative buffer material that forms a type-I band alignment with these absorbers, where the conduction band minimum and the valence band maximum are both localized on the absorber side.

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“…However, our DFT modeling of band offsets for idealized model interfaces between CuInSe 2 and KInSe 2 , RbInSe 2 , and CsInSe 2 shows actually downward shifts of the conduction band edge, see Figure S2 in the Supporting Information. The recent DFT modeling by Ghorbani et al predicts that Cu deficiency shifts the conduction band of CuInSe 2 downward but this cannot totally cancel the computed downward shift of the conduction band from CuInSe 2 to alkali secondary phases (Figure S2, Supporting Information), even in the case of the smallest shift for KInSe 2 . Resolution for this discrepancy between experimental and theoretical findings remains a topic of future research.…”

Section: Effects Of Post‐deposition Treatment With Heavy Alkalismentioning

confidence: 92%

Heavy Alkali Treatment of Cu(In,Ga)Se₂Solar Cells: Surface versus Bulk Effects

Siebentritt

Avancini

Bär

et al. 2020

Advanced Energy Materials

122

195

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Chalcopyrite solar cells achieve efficiencies above 23%. The latest improvements are due to post‐deposition treatments (PDT) with heavy alkalis. This study provides a comprehensive description of the effect of PDT on the chemical and electronic structure of surface and bulk of Cu(In,Ga)Se2. Chemical changes at the surface appear similar, independent of absorber or alkali. However, the effect on the surface electronic structure differs with absorber or type of treatment, although the improvement of the solar cell efficiency is the same. Thus, changes at the surface cannot be the only effect of the PDT treatment. The main effect of PDT with heavy alkalis concerns bulk recombination. The reduction in bulk recombination goes along with a reduced density of electronic tail states. Improvements in open‐circuit voltage appear together with reduced band bending at grain boundaries. Heavy alkalis accumulate at grain boundaries and are not detected in the grains. This behavior is understood by the energetics of the formation of single‐phase Cu‐alkali compounds. Thus, the efficiency improvement with heavy alkali PDT can be attributed to reduced band bending at grain boundaries, which reduces tail states and nonradiative recombination and is caused by accumulation of heavy alkalis at grain boundaries.

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Energy level alignment of Cu(In,Ga)(S,Se)2 absorber compounds with

Cited by 20 publications

References 56 publications

Influence of Substrate Temperature during InxSy Sputtering on Cu(In,Ga)Se2/Buffer Interface Properties and Solar Cell Performance

Influence of Substrate Temperature during InxSy Sputtering on Cu(In,Ga)Se2/Buffer Interface Properties and Solar Cell Performance

On efficiency of earth-abundant chalcogenide photovoltaic materials buffered with CdS: the limiting effect of band alignment

Heavy Alkali Treatment of Cu(In,Ga)Se₂Solar Cells: Surface versus Bulk Effects

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Energy level alignment of Cu(In,Ga)(S,Se)2 absorber compounds with

Cited by 20 publications

References 56 publications

Influence of Substrate Temperature during InxSy Sputtering on Cu(In,Ga)Se2/Buffer Interface Properties and Solar Cell Performance

Influence of Substrate Temperature during InxSy Sputtering on Cu(In,Ga)Se2/Buffer Interface Properties and Solar Cell Performance

On efficiency of earth-abundant chalcogenide photovoltaic materials buffered with CdS: the limiting effect of band alignment

Heavy Alkali Treatment of Cu(In,Ga)Se2Solar Cells: Surface versus Bulk Effects

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Heavy Alkali Treatment of Cu(In,Ga)Se₂Solar Cells: Surface versus Bulk Effects