References of "Spindler, Conrad 50003134"
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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 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 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 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 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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See detailOptical Detection of Deep Defects in Cu(In,Ga)Se2
Spindler, Conrad UL

Doctoral thesis (2018)

The aim of this thesis is to shed light on the deep defect structure in Cu(In,Ga)Se2 by photoluminescence measurements and to propose a possible conclusive defect model by attributing experimental ... [more ▼]

The aim of this thesis is to shed light on the deep defect structure in Cu(In,Ga)Se2 by photoluminescence measurements and to propose a possible conclusive defect model by attributing experimental findings to a literature review of defect calculations from first principles. Epitaxial films are grown on GaAs by metal organic vapor phase epitaxy and characterized by photoluminescence at room or low temperature. In CuGaSe2, deep defect bands at ca. 1.1 eV and 1.23 eV are resolved. A model for the power law behavior in excitation dependent measurements of the peak intensities is derived, which leads to the experimental finding of two deep donor-like defects as a result. In Cu(In,Ga)Se2, the deeper band at around 1.1 eV remains constant in energy when more and more gallium is replaced by indium in the solid solution. For decreasing Ga-contents, the band gap is mainly lowered by a decrease of the conduction band energy. From fitting models for electron-phonon coupling, the dominating deep donor-like defect is determined at 1.3 eV above the valence band maximum. This level is proposed to be crucial for high Ga-contents when it is deep inside the band gap and most likely acts as a recombination center. At low Ga-contents it is resonant with the conduction band. The larger open circuit voltage deficits for high Ga-contents are proposed to stem at least partly from this defect which is qualitatively supported by simulations. Additionally another defect band at around 0.7 eV is observed for high Ga-contents at low temperatures and at 0.8 eV for low Ga-contents. The intensity of the 0.8 eV band seems to disappear in a sample with Cu-deficiency. In general, deep luminescence is always observed with similar energies in all Cu-rich compositions, independent of the Ga-content. The deep defect involved could explain inferior efficiencies of Cu-rich devices which show increased non-radiative recombination in general. It is further discussed that the same deep defect could be the origin of a level at 0.8 eV which is observed in several photo-capacitance measurements in literature. Based on the literature review for intrinsic defect calculations by hybrid-functionals, a possible defect model for shallow and deep defects is derived with a focus on those results, where different authors using different methods agree. By comparing the experimental results in the scope of this thesis, the deep defect found at 1.3 eV above the valence band is attributed to the GaCu antisites. The single (0/-1) charge transition of CuIn and CuGa is proposed to be the main shallow acceptor in the near-band-edge luminescence of Cu-rich compositions at 60 - 100 meV, whereas the second (-1/-2) charge transition is attributed to the deep 0.8 eV defect band. The present findings could be useful for the improvement of Cu(In,Ga)Se2 solar cells with stochiometric absorber compositions (Cu-rich growth) or with high band gaps (high Ga-content). Furthermore, the results show a very good agreement of experiment and recent theoretical calculations of defects, which can be seen as a promising relation between photoluminescence spectroscopy and predictions from theory for other complex materials. [less ▲]

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See detailSynthesis, theoretical and experimental characterisation of thin film Cu2Sn1-xGexS3 ternary alloys (x = 0 to 1): Homogeneous intermixing of Sn and Ge
Robert, Erika UL; Gunder, René; De Wild, Jessica UL et al

in Acta Materialia (2018), 151

Cu2Sn1-xGexS3 is a p-type semiconductor alloy currently investigated for use as an absorber layer in thin film solar cells. The aim of this study is to investigate the properties of this alloy in thin ... [more ▼]

Cu2Sn1-xGexS3 is a p-type semiconductor alloy currently investigated for use as an absorber layer in thin film solar cells. The aim of this study is to investigate the properties of this alloy in thin film form in order to establish relationships between group IV composition and structural, vibrational and opto-electronic properties. Seven single phase Cu2Sn1-xGexS3 films are prepared from x ¼ 0 to 1, showing a uniform distribution of Ge and Sn laterally and in depth. The films all show a monoclinic crystal structure. The lattice parameters are extracted using Le Bail refinement and show a linear decrease with increasing Ge content. Using density-functional theory with hybrid functionals, we calculate the Raman active phonon frequencies of Cu2SnS3 and Cu2GeS3. For the alloyed compounds, we use a virtual atom approximation. The shift of the main Raman peak from x ¼ 0 to x ¼ 1 can be explained as being half due to the change in atomic masses and half being due to the different bond strength. The bandgaps of the alloys are extracted from photoluminescence measurements and increase linearly from about 0.90 to 1.56 eV with increasing Ge. The net acceptor density of all films is around 1018 cm 3. These analyses have established that the alloy forms a solid solution over the entire composition range meaning that intentional band gap grading should be possible for future absorber layers. The linear variation of the unit cell parameters and the band gap with group IV content allows composition determination by scattering or optical measurements. Further research is required to reduce the doping density by two orders of magnitude in order to improve the current collection within a solar cell device structure. [less ▲]

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See detailSodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers
Colombara, Diego UL; Werner, Florian UL; Schwarz, Torsten et al

in Nature Communications (2018)

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See detailInterdiffusion and Doping Gradients at the Buffer/Absorber Interface in Thin-Film Solar Cells
Werner, Florian UL; Babbe, Finn UL; Burkhart, Jan UL et al

in ACS Applied Materials and Interfaces (2018), 10

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See detailDefects in Cu(In,Ga)Se2: Photoluminescence vs Theory
Spindler, Conrad UL

Poster (2018)

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See detailAbsorption Coefficient of a Semiconductor Thin Film from Photoluminescence
Rey, Germain UL; Spindler, Conrad UL; Rachad, Wafae UL et al

in Physical Review Applied (2018), 9

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See detailLuminescence detection of the 0.8 eV defect
Spindler, Conrad UL

Poster (2017)

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See detailExcitation dependence of photoluminescence transitions
Spindler, Conrad UL

Poster (2016)

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See detailOrdering kesterite improves solar cells:A low temperature post-deposition annealing study
Rey, Germain UL; Weiss, Thomas UL; Sendler, Jan UL et al

in Solar Energy Materials and Solar Cells (2016), 151

Detailed reference viewed: 270 (18 UL)