Investigation of the potassium fluoride post deposition treatment on the CIGSe/CdS interface using hard X-ray photoemission spectroscopy – a comparative study

Ümsür, Bünyamin; Calvet, Wolfram; Steigert, Alexander; Lauermann, Iver; Gorgoi, Mihaela; Prietzel, Karsten; Greiner, D.; Kaufmann, Christian A.; Unold, Thomas; Lux‐Steiner, Martha Ch.

doi:10.1039/c6cp00260a

Cited by 26 publications

(10 citation statements)

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“…Different from the behavior of Ga, In, and Se, we find a strong reduction of the Cu 2p signal on the ZSW absorber surface after RbF PDT. This is in accordance with other studies observing such a reduction in Cu content at the CIGSSe surface after KF PDT, but in contrast to studies suggesting a complete KF PDT‐induced removal of Cu from the surface . Besides these changes of the surface stoichiometry, K or (in the ZSW case) Rb is observed on the absorber surface after PDT, while a reduction of Na occurs (see Figure and refs.…”

Section: The Chemical Structure Of Thin‐film Solar Cell Surfaces and supporting

confidence: 92%

Surface and Interface Properties in Thin‐Film Solar Cells: Using Soft X‐rays and Electrons to Unravel the Electronic and Chemical Structure

2019

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Thin‐film solar cells have great potential to overtake the currently dominant silicon‐based solar cell technologies in a strongly growing market. Such thin‐film devices consist of a multilayer structure, for which charge‐carrier transport across interfaces plays a crucial role in minimizing the associated recombination losses and achieving high solar conversion efficiencies. Further development can strongly profit from a high‐level characterization that gives a local, electronic, and chemical picture of the interface properties, which allows for an insight‐driven optimization. Herein, the authors' recent progress of applying a “toolbox” of high‐level laboratory‐ and synchrotron‐based electron and soft X‐ray spectroscopies to characterize the chemical and electronic properties of such applied interfaces is provided. With this toolbox in hand, the activities are paired with those of experts in thin‐film solar cell preparation at the cutting edge of current developments to obtain a deeper understanding of the recent improvements in the field, e.g., by studying the influence of so‐called “post‐deposition treatments”, as well as characterizing the properties of interfaces with alternative buffer layer materials that give superior efficiencies on large, module‐sized areas.

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Section: The Chemical Structure Of Thin‐film Solar Cell Surfaces and supporting

confidence: 92%

Surface and Interface Properties in Thin‐Film Solar Cells: Using Soft X‐rays and Electrons to Unravel the Electronic and Chemical Structure

2019

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“…In this context, the postdeposition processes involving KF have been shown to cause a Cu-and Ga-depleted surface region [3], [6]. The surface region is thought to facilitate the in-diffusion of cadmium and consequently the formation of Cd Cu donor levels during the deposition of CdS [3], [7], [8]. Furthermore, the NaF + KF PDT also induces a band gap widening at the absorber surface [6], [9].…”

Section: Influence Of Sodium and Rubidium Postdeposition Treatment Onmentioning

confidence: 99%

Influence of Sodium and Rubidium Postdeposition Treatment on the Quasi-Fermi Level Splitting of Cu(In,Ga)Se₂Thin Films

Wolter

Bissig

Avancini

et al. 2018

IEEE J. Photovoltaics

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The influence of sodium and rubidium postdeposition treatment on the quality of Cu(In,Ga)Se 2 thin-film absorbers is investigated. The quasi-Fermi level splitting (QFLS), measured via photoluminescence (PL), is used as the metric of quality of the absorber. To evaluate the QFLS values in the graded absorber of state-of-the-art devices, it is necessary to know at which location the luminescence is generated. Here we show, by measuring the PL in different geometries, that the photons originate from the global band gap minimum inside the bulk. We use this knowledge to compare the QFLS in different absorbers, where our results show that the QFLS is higher in absorbers that were treated with NaF + RbF than in absorbers that were only treated with NaF or not treated at all. We attribute this increase to a reduced nonradiative recombination, even before cadmium sulfide deposition. A decreased difference between QFLS and open-circuit voltage in the corresponding finished solar cells also reveals an improved CdS/CIGS interface. Both effects ultimately lead to a higher efficiency. I. INTRODUCTION T HE beneficial effects of alkali elements, especially sodium, on the performance of chalcopyrite solar cells based on Cu(In,Ga)Se 2 (CIGS) absorbers were discovered more than 20 years ago [1]. It was found that Na naturally diffuses from the alkali containing soda lime glass (SLG) substrate into the absorber during the high-temperature growth process. In solar cells grown on alkali-free substrates, such as the flexible polyimide films, the alkali elements would need to be added extrinsically in order

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“…Studies concerning the electronic structure of the CIGS surface and CIGS/CdS interface using ultraviolet photoelectron spectroscopy (UPS) and X‐ray photoelectron spectroscopy (XPS) as well as inverse photoemission spectroscopy (IPES) measurements have been given as a result of the downward shift of the valence band maximum (VBM) at the absorber surface after PDT . Contradictory results were also reported; in the case of KF, an upward shift of the VBM was derived from hard X‐ray photoelectron spectroscopy (HAXPES). Similar discrepancy has also occurred while comparing the conduction band minimum (CBM) between untreated/treated PDT samples .…”

Section: Introductionmentioning

confidence: 99%

Limitation of Current Transport across the Heterojunction in Cu(In,Ga)Se₂Solar Cells Prepared with Alkali Fluoride Postdeposition Treatment

et al. 2020

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Postdeposition treatments (PDTs) of chalcopyrite absorbers with alkali fluorides have contributed to improving the efficiency of corresponding solar cell devices. However, cells prepared with PDTs also tend to exhibit nonideal current–voltage (J–V) characteristics especially at low temperatures. These include blocking of the forward diode current, saturation of the open‐circuit voltage with respect to temperature, a discrepancy between dark and Jsc (Voc) characteristics, and a crossover between dark and light J–V curves. These are typical observations while measuring the temperature‐dependent J–V characteristics. Herein, the influence of electronic material parameters on the blocking of the current across the heterojunction in numerical simulations is reported. It is shown that a low‐doped ZnO window layer, acceptor defects at the CdS/ZnO interface, or a high band offset at that interface lead to similar nonideal J–V characteristics, suggesting that the carrier density in the buffer layer is a crucial parameter for the current limitation. Connections between the effects of PDT previously reported in literature and the electronic material parameters considered in the numerical model are discussed to explain the nonideal J–V characteristics caused by the PDTs.

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Investigation of the potassium fluoride post deposition treatment on the CIGSe/CdS interface using hard X-ray photoemission spectroscopy – a comparative study

Abstract: Modifications at the CIGSe/CdS interface due to KF-PDT are studied using synchrotron radiation.

Cited by 26 publications

References 33 publications

Surface and Interface Properties in Thin‐Film Solar Cells: Using Soft X‐rays and Electrons to Unravel the Electronic and Chemical Structure

Surface and Interface Properties in Thin‐Film Solar Cells: Using Soft X‐rays and Electrons to Unravel the Electronic and Chemical Structure

Influence of Sodium and Rubidium Postdeposition Treatment on the Quasi-Fermi Level Splitting of Cu(In,Ga)Se₂Thin Films

Limitation of Current Transport across the Heterojunction in Cu(In,Ga)Se₂Solar Cells Prepared with Alkali Fluoride Postdeposition Treatment

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Investigation of the potassium fluoride post deposition treatment on the CIGSe/CdS interface using hard X-ray photoemission spectroscopy – a comparative study

Abstract: Modifications at the CIGSe/CdS interface due to KF-PDT are studied using synchrotron radiation.

Cited by 26 publications

References 33 publications

Surface and Interface Properties in Thin‐Film Solar Cells: Using Soft X‐rays and Electrons to Unravel the Electronic and Chemical Structure

Surface and Interface Properties in Thin‐Film Solar Cells: Using Soft X‐rays and Electrons to Unravel the Electronic and Chemical Structure

Influence of Sodium and Rubidium Postdeposition Treatment on the Quasi-Fermi Level Splitting of Cu(In,Ga)Se2Thin Films

Limitation of Current Transport across the Heterojunction in Cu(In,Ga)Se2Solar Cells Prepared with Alkali Fluoride Postdeposition Treatment

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Product

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Influence of Sodium and Rubidium Postdeposition Treatment on the Quasi-Fermi Level Splitting of Cu(In,Ga)Se₂Thin Films

Limitation of Current Transport across the Heterojunction in Cu(In,Ga)Se₂Solar Cells Prepared with Alkali Fluoride Postdeposition Treatment