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  Handick, Evelyn: Surface and Interface Characterization by X-ray and Electron Spectroscopies - Revealing the Peculiarities of Cu(In,Ga)Se₂ Chalcopyrite and CH₃NH₃PbI_3-xCl_x Perovskite-based Thin-film Solar Cell Structures. , Cottbus, Brandenburgische Technische Universität (BTU), Diss., 2016
  https://opus4.kobv.de/opus4-btu/files/4243/Handick_Evelyn.pdf

Open Access Version

Abstract:
This thesis focuses on the investigation and characterization of the surfaces and interfaces of chalcopyrite-based Cu(In,Ga)Se2 (CIGSe) and organo-metal mixed halide perovskites, specifically CH3NH3PbI(3-x)Clx thin film solar cell absorbers using various x-ray and electron spectroscopies. In particular, the impact of alkali treatments on the chemical and electronic surface and near-surface structure of CIGSe absorbers is studied. For CH3NH3PbI(3-x)Clx the compound formation is monitored and the peculiarities of the interface formation of CH3NH3PbI(3-x)Clx on compact and mesoporous TiO2 are examined. Laboratory and synchrotron-based photoelectron spectroscopy are used to gain a depth-dependent picture of the chemical and electronic structure in the surface and near-surface region of CIGSe absorbers, focusing on the influence of NaF and NaF/KF post-deposition treatments (PDT) when compared to alkali-free CIGSe absorbers. The alkali-free and NaF-PDT absorbers show similar chemical properties, having a Cu and Ga poor surface region compared to the nominal bulk and the same chemical environment for indium and selenium. For the NaF/KF-PDT samples a K-In-Se compound is present on top of a Cu-In-Ga-Se compound, with a nanopatterned surface. The NaF/KF-PDT has a surface regionthat is almost devoid of Cu and Ga. Further, for the NaF-PDT sample a near-surface electronic band gap of ?? eV is derived. In contrast, a large and more gradual change towards the surface is obtained for the NaF/KF-PDT absorber with exhibiting a significant band gap widening of the surface, which is ascribed in agreement withto a Cu- and Ga-devoid surface region and the formation of a K-In-Se surface compound. To in-situ monitor the compound formation of CH3NH3PbI(3-x)Clx on compact TiO2 (c-TiO2) hard x-ray photoelectron spectroscopy is used. While During in-situ annealing a drop-casted layer of precursor solution on c-TiO2 shifts in the perovskite related core levels can be observed upon reach during the “transition temperature” of 80-100°C are observed. Further the Cl signal decrease at the onset of annealing and shows a depletion in the surface region above for annealing temperatures of above 50°C. FurtherIn addition, the chemical and electronic structure of the interface between perovskite and mesoporous TiO2 (mp-TiO2) or c-TiO2 using different perovskite layer thicknesses are studied. For both structures core level and VBM shifts are determined upon interface formation .