Rubidium segregation at random grain boundaries in Cu(In,Ga)Se2 absorbers

Schöppe, Philipp; Schönherr, Sven; Wuerz, Roland; Wisniewski, Wolfgang; Martı́nez-Criado, Gema; Ritzer, Maurizio; Ritter, Konrad; Ronning, Carsten; Schnohr, Claudia

doi:10.1016/j.nanoen.2017.10.063

Cited by 77 publications

(68 citation statements)

References 30 publications

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“…Concerning absorber elements, in both cases, Cu depletion and In enrichment are observed at the grain boundary, the latter being slightly more pronounced when the RbF‐PDT is applied. Accumulation of Rb at grain boundaries and dislocation cores has also been observed by TEM and X‐ray fluorescence investigations of RbF‐treated Cu(In,Ga)Se 2 absorbers and has been proposed as the cause of reduced bulk recombination …”

Section: Effects Of Post‐deposition Treatment With Heavy Alkalismentioning

confidence: 81%

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

Siebentritt

Avancini

Bär

et al. 2020

Advanced Energy Materials

125

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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Section: Effects Of Post‐deposition Treatment With Heavy Alkalismentioning

confidence: 81%

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

Siebentritt

Avancini

Bär

et al. 2020

Advanced Energy Materials

125

195

View full text Add to dashboard Cite

show abstract

“…33 Recent experimental results suggest that the heavy alkali metal (like Rb) segregates at GBs, at dislocation cores, and at the interface between CIGS/MoSe 2 layer. [33][34][35] Cs, which has a significantly larger ionic radii than Rb is more favorable to segregate at these regions. This is also supported by our SEM photograph (see Figure S1),…”

Section: Sims Analysis Of Csf-treated Cigs Solar Cells Before and Amentioning

confidence: 99%

Effect of heat‐bias soaking on cesium fluoride‐treated CIGS thin film solar cells

Khatri

Matsuura

Sugiyama

et al. 2018

Progress in Photovoltaics

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The combined effect of heating and forward bias voltage, that is, heat‐bias soaking (HBS) on cesium fluoride (CsF)‐free and CsF‐treated Cu(In1‐xGax)Se2 (CIGS) solar cells using chemical bath deposition‐cadmium sulfide (CBD‐CdS) buffer layer was investigated with varying the heating temperature, bias voltage, and biasing time. Heat bias soaking followed by heat soaking (HS) (ie, HBS/HS) treatments improved the open‐circuit voltage (VOC) and conversion efficiency for the CsF‐treated CIGS solar cell, whereas such a beneficial effect was not observed for CsF‐free CIGS solar cells. Capacitance‐voltage measurement confirmed the significantly increased carrier concentration (NCV) after HBS for the CsF‐CIGS solar cell, which is one of the possible reasons for the increased VOC. Because of the extremely high NCV, the short‐circuit current density (JSC) decreased owing to the narrower depletion width. However, the high NCV could be tuned to an appropriate value via a subsequent moderate heating procedure without biasing. As a result, the JSC loss was reduced, thereby improving the cell efficiency. These results open a new route to improve the efficiency of alkali‐treated CIGS solar cells.

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“…Regarding Cu(In 1−x ,Ga x )Se 2 (CIGS) thin film solar cells fabricated onto sodium‐free substrates such as polyimide, the beneficial effects of sodium fluoride post‐deposition treatment (NaF‐PDT) was initially discovered by the Swiss Federal Laboratories for Materials Science and Technology (EMPA) group. Since this discovery, several works have been carried out on alkali‐metal (Na, K, Rb, Cs) PDT to achieve high‐efficiency CIGS solar cells. In recent years, the alkali‐metal PDT technology dramatically improved the conversion efficiency of CIGS‐based solar cells and modules, which was 22.6 and 22.9% for small‐area cells and 19.2% for 30 × 30 cm 2 submodules.…”

Section: Basic Cell Parameters Of the Naf‐free And Naf‐treated Cigs Smentioning

confidence: 99%

Tunable Carrier Concentration of NaF‐Treated CIGS Solar Cells Using Heat–Light Soaking and Subsequent Heating

Matsuura

Shudo

Khatri

et al. 2018

Physica Rapid Research Ltrs

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The combined effect of the heat–light soaking (HLS) and subsequent heat‐soaking (HS) processes is investigated on NaF‐free and NaF‐treated CIGS solar cells with CdS buffer layer. The HLS treatment improves cell efficiency slightly with increased open‐circuit voltage for NaF‐treated CIGS solar cells, whereas the cell efficiency deteriorates for NaF‐free CIGS solar cells. The different behaviors between both types of solar cells may be due to a Na‐containing new layer, which is formed at the CIGS surface region by NaF‐treatment. On the other hand, the short‐circuit current density (JSC) decreases for both types of solar cells after HLS treatment, which is attributed to the extremely high carrier concentration (NCV), leading to a narrower space charge region. However, it is found that the large NCV can be tuned to an appropriate value using the subsequent HS technique. As a result, the JSC loss is successfully reduced, therefore improving cell efficiency. The details of this improved efficiency are discussed with respect to the change of NCV in CIGS solar cells by the HLS and HS processes.

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Rubidium segregation at random grain boundaries in Cu(In,Ga)Se2 absorbers

Cited by 77 publications

References 30 publications

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

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

Effect of heat‐bias soaking on cesium fluoride‐treated CIGS thin film solar cells

Tunable Carrier Concentration of NaF‐Treated CIGS Solar Cells Using Heat–Light Soaking and Subsequent Heating

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Rubidium segregation at random grain boundaries in Cu(In,Ga)Se2 absorbers

Cited by 77 publications

References 30 publications

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

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

Effect of heat‐bias soaking on cesium fluoride‐treated CIGS thin film solar cells

Tunable Carrier Concentration of NaF‐Treated CIGS Solar Cells Using Heat–Light Soaking and Subsequent Heating

Contact Info

Product

Resources

About

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

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