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See detailThe impact of Kelvin probe force microscopy operation modes and environment on grain boundary band bending in perovskite and Cu(In,Ga)Se2 solar cells
Martin Lanzoni, Evandro UL; Gallet, Thibaut UL; Spindler, Conrad UL et al

in Nano Energy (2021), 88

An in-depth understanding of the electronic properties of grain boundaries (GBs) in polycrystalline semiconductor absorbers is of high importance since their charge carrier recombination rates may be very ... [more ▼]

An in-depth understanding of the electronic properties of grain boundaries (GBs) in polycrystalline semiconductor absorbers is of high importance since their charge carrier recombination rates may be very high and hence limit the solar cell device performance. Kelvin Probe Force Microscopy (KPFM) is the method of choice to investigate GB band bending on the nanometer scale and thereby helps to develop passivation strategies. Here, it is shown that the workfunction, measured with amplitude modulation (AM)-KPFM, which is by far the most common KPFM measurement mode, is prone to exhibit measurement artifacts at grain boundaries on typical solar cell absorbers such as Cu(In,Ga)Se2 and CH3NH3PbI3. This is a direct consequence of a change in the cantilever–sample distance that varies on rough samples. Furthermore, we critically discuss the impact of different environments (air versus vacuum) and show that air exposure alters the GB and facet contrast, which leads to erroneous interpretations of the GB physics. Frequency modulation (FM)-KPFM measurements on non-air-exposed CIGSe and perovskite absorbers show that the amount of band bending measured at the GB is negligible and that the electronic landscape of the semiconductor surface is dominated by facet-related contrast due to the polycrystalline nature of the absorbers. [less ▲]

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See detailThe effect of KF post-deposition treatments on the optoelectronic properties of Cu(In,Ga)Se2 single crystals
Ramirez Sanchez, Omar UL; Bertrand, Maud; Debot, Alice UL et al

in Solar RRL (2021)

The power conversion efficiency boost of Cu(In,Ga)Se2 in the past years has been possible due to the incorporation of heavy alkali atoms. Their addition through post-deposition treatments results in an ... [more ▼]

The power conversion efficiency boost of Cu(In,Ga)Se2 in the past years has been possible due to the incorporation of heavy alkali atoms. Their addition through post-deposition treatments results in an improvement of the open-circuit voltage, which origin has been associated with grain boundaries. The present work discusses the effect of potassium fluoride post-deposition treatments on the optoelectronic properties of a series of sodium-free Cu(In,Ga)Se2 single crystals with varying Cu and Ga content. Results suggest that improvement of the quasi-Fermi level splitting can be achieved despite the absence of grain boundaries, being greater in low-gallium Cu-poor absorbers. Secondary ion mass spectrometry reveals the presence of potassium inside the bulk of the films, suggesting that transport of potassium can occur through grain interiors. In addition, a type inversion from n to p in KF-treated low-gallium Cu(In,Ga)Se2 is observed, which along a carrier lifetime study demonstrates that potassium can act as a dopant. The fact that potassium by its own can alter the optoelectronic properties of Cu(In,Ga)Se2 single crystals demonstrates that the effect of post-deposition treatments goes beyond grain boundary passivation. [less ▲]

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See detailHow band tail recombination influences the open-circuit voltage of solar cells.
Wolter, Max UL; Carron, Romain; Avancini, Enrico et al

in Progress in Photovoltaics (2021)

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See detailAbsorber composition: A critical parameter for the effectiveness of heat treatments in chalcopyrite solar cells
Sood, Mohit UL; Elanzeery, Hossam UL; Adeleye, Damilola UL et al

in Progress in Photovoltaics (2020)

Post-device heat treatment (HT) in chalcopyrite [Cu(In,Ga)(S,Se)2] solar cells is known to improve the performance of the devices. However, this HT is only beneficial for devices made with absorbers grown ... [more ▼]

Post-device heat treatment (HT) in chalcopyrite [Cu(In,Ga)(S,Se)2] solar cells is known to improve the performance of the devices. However, this HT is only beneficial for devices made with absorbers grown under Cu-poor conditions but not under Cu excess.. We present a systematic study to understand the effects of HT on CuInSe2 and CuInS2 solar cells. The study is performed for CuInSe2 solar cells grown under Cu-rich and Cu-poor chemical potential prepared with both CdS and Zn(O,S) buffer layers. In addition, we also study Cu-rich CuInS2 solar cells prepared with the suitable Zn(O,S) buffer layer. For Cu-poor selenide device low-temperature HT leads to passivation of bulk, whereas in Cu-rich devices no such passivation was observed. The Cu-rich devices are hampered by a large shunt. The HT decreases shunt resistance in Cu-rich selenides, whereas it increases shunt resistance in Cu-rich sulfides.. The origin of these changes in device performance was investigated with capacitance-voltage measurement which shows the considerable decrease in carrier concentration with HT in Cu-poor CuInSe2, and temperature dependent current-voltage measurements show the presence of barrier for minority carriers. Together with numerical simulations, these findings support a highly-doped interfacial p+ layer device model in Cu-rich selenide absorbers and explain the discrepancy between Cu-poor and Curich device performance. Our findings provide insights into how the same treatment can have a completely different effect on the device depending on the composition of the absorber. [less ▲]

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See detailPassivation of the CuInSe2 surface via cadmium pre-electrolyte treatment
Kameni Boumenou, Christian UL; Babbe, Finn; Elizabeth, Amala et al

in Physical Review Materials (2020)

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See detailPhonon coupling and shallow defects in CuInS2
Lomuscio, Alberto UL; Sood, Mohit UL; Melchiorre, Michele UL et al

in Physical Review. B (2020), 101(8), 085119-

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See detailSurface characterization of epitaxial Cu-rich CuInSe2 absorbers
Lanzoni, Evandro; Spindler, Conrad UL; Ramirez Sanchez, Omar UL et al

in IEEE (2020)

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See detailOn the chemistry of grain boundaries in CuInS2 film
Schwarz, Torsten; Lomuscio, Alberto UL; Siebentritt, Susanne UL et al

in Nano Energy (2020), 76

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See detailPhotoluminescence-Based Method for Imaging Buffer Layer Thickness in CIGS Solar Cells
Rey, Germain UL; Paduthol, Appu; Sun, Kaiwen et al

in IEEE Journal of Photovoltaics (2020)

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See detailOxidation as Key Mechanism for Efficient Interface Passivation in Cu(In,Ga)Se2 Thin-Film Solar Cells
Werner, Florian UL; Veith-Wolf, Boris; Spindler, Conrad UL et al

in Physical Review Applied (2020)

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See detailChemical instability at chalcogenide surfaces impacts chalcopyrite devices well beyond the surface
Colombara, Diego UL; Elanzeery, Hossam UL; Nicoara, Nicoleta et al

in Nature Communications (2020)

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See detailHeavy Alkali Treatment of Cu(In,Ga)Se2 Solar Cells: Surface versus Bulk effects
Siebentritt, Susanne UL; Avancini, Enrico; Bär, Marcus et al

in Advanced Energy Materials (2020)

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See detailElectronic defects in Cu(In,Ga)Se2: Towards a comprehensive model
Spindler, Conrad UL; Babbe, Finn UL; Wolter, Max UL et al

in Physical Review Materials (2019), 3

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See detailSurface characterization of epitaxial Cu-rich CuInSe2 absorbers
Martin Lanzoni, Evandro UL; Spindler, Conrad UL; Ramirez Sanchez, Omar UL et al

in IEEE Photovoltaic Specialists Conference. Conference Record (2019, July)

We investigated the electrical properties of epitaxial Cu-rich CuInSe 2 by Kelvin probe force microscopy (KPFM) under ambient and ultra-high vacuum conditions. We first measured the sample under ambient ... [more ▼]

We investigated the electrical properties of epitaxial Cu-rich CuInSe 2 by Kelvin probe force microscopy (KPFM) under ambient and ultra-high vacuum conditions. We first measured the sample under ambient conditions before and after potassium cyanide (KCN) etching. In both cases, we do not see any substantial contrast in the surface potential data; furthermore, after the KCN etching we observed outgrowths with a height around 2nm over the sample surface. On the other hand, the KPFM measurements under ultra-high vacuum conditions show a work function dependence according to the surface orientation of the Cu-rich CuInSe 2 crystal. Our results show the possibility to increase the efficiency of epitaxial Cu-rich CuInSe 2 by growing the materials in the appropriated surface orientation where the variations in work function are reduced. [less ▲]

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