Spectroscopy of electronic defect states in Cu(In, Ga)(S, Se)2_2-based heterojunctions and Schottky diodes under damp-heat exposure

The changes of defect characteristics induced by accelerated lifetime tests on the heterostructure n-ZnO/i-ZnO/CdS/Cu(In, Ga)(S, Se)$_2$/Mo relevant for photovoltaic energy conversion are investigated. We subject heterojunction and Schottky devices to extended damp heat exposure at 85$^{\circ}$C ambient temperature and 85% relative humidity for various time periods. In order to understand the origin of the pronounced changes of the devices, we apply current--voltage and capacitance--voltage measurements, admittance spectroscopy, and deep-level transient spectroscopy. The fill factor and open-circuit voltage of test devices are reduced after prolonged damp heat treatment, leading to a reduced energy conversion efficiency. We observe the presence of defect states in the vicinity of the CdS/chalcopyrite interface. Their activation energy increases due to damp heat exposure, indicating a reduced band bending at the Cu(In, Ga)(S, Se)$_2$ surface. The Fermi-level pinning at the buffer/chalcopyrite interface, maintaining a high band bending in as-grown cells, is lifted due to the damp-heat exposure. We also observe changes in the bulk defect spectra due to the damp-heat treatment.Comment: 4 pages, 5 figure

Rubidium Fluoride Post-Deposition Treatment: Impact on the Chemical Structure of the Cu(In,Ga)Se2 Surface and CdS/Cu(In,Ga)Se2 Interface in Thin-Film Solar Cells.

We present a detailed characterization of the chemical structure of the Cu(In,Ga)Se2 thin-film surface and the CdS/Cu(In,Ga)Se2 interface, both with and without a RbF post-deposition treatment (RbF-PDT). For this purpose, X-ray photoelectron and Auger electron spectroscopy, as well as synchrotron-based soft X-ray emission spectroscopy have been employed. Although some similarities with the reported impacts of light-element alkali PDT (i.e., NaF- and KF-PDT) are found, we observe some distinct differences, which might be the reason for the further improved conversion efficiency with heavy-element alkali PDT. In particular, we find that the RbF-PDT reduces, but not fully removes, the copper content at the absorber surface and does not induce a significant change in the Ga/(Ga + In) ratio. Additionally, we observe an increased amount of indium and gallium oxides at the surface of the treated absorber. These oxides are partly (in the case of indium) and completely (in the case of gallium) removed from the CdS/Cu(In,Ga)Se2 interface by the chemical bath deposition of the CdS buffer

DLTS investigations on CIGS solar cells from an inline co-evaporation system with RbF post-deposition treatment

In this study, Deep Level Transient Spectroscopy (DLTS) measurements have been performed on Cu(In,Ga)Se$_{2}$ (CIGS) solar cells from an inline co-evaporation system. The focus of this investigation is directed on the effect of rubidium-fluoride (RbF)-post-deposition treatment (PDT) on the defects in the CIGS absorber layer. Different traps can be identified and their properties are calculated. Herein, different methods of evaluations have been used to verify the results. Specifically, one minority trap around 400 meV was found to show a significant reduction of the trap density due to the alkali treatment. In contrast, a majority trap at approximately 600 meV is unaffected

History-dependent domain and skyrmion formation in 2D van der Waals magnet Fe3GeTe2

The discovery of two-dimensional magnets has initiated a new field of research, exploring both fundamental low-dimensional magnetism, and prospective spintronic applications. Recently, observations of magnetic skyrmions in the 2D ferromagnet Fe3GeTe2 (FGT) have been reported, introducing further application possibilities. However, controlling the exhibited magnetic state requires systematic knowledge of the history-dependence of the spin textures, which remains largely unexplored in 2D magnets. In this work, we utilise real-space imaging, and complementary simulations, to determine and explain the thickness-dependent magnetic phase diagrams of an exfoliated FGT flake, revealing a complex, history-dependent emergence of the uniformly magnetised, stripe domain and skyrmion states. The results show that the interplay of the dominant dipolar interaction and strongly temperature dependent out-of-plane anisotropy energy terms enables the selective stabilisation of all three states at zero field, and at a single temperature, while the Dzyaloshinksii-Moriya interaction must be present to realise the observed Néel-type domain walls. The findings open perspectives for 2D devices incorporating topological spin textures

2D/3D Heterostructure for Semitransparent Perovskite Solar Cells with Engineered Bandgap Enables Efficiencies Exceeding 25% in Four‐Terminal Tandems with Silicon and CIGS

Wide-bandgap perovskite solar cells (PSCs) with optimal bandgap (E$_{g}$) and high power conversion efficiency (PCE) are key to high-performance perovskite-based tandem photovoltaics. A 2D/3D perovskite heterostructure passivation is employed for double-cation wide-bandgap PSCs with engineered bandgap (1.65 eV ≤ E$_{g}$ ≤ 1.85 eV), which results in improved stabilized PCEs and a strong enhancement in open-circuit voltages of around 45 mV compared to reference devices for all investigated bandgaps. Making use of this strategy, semitransparent PSCs with engineered bandgap are developed, which show stabilized PCEs of up to 25.7% and 25.0% in fourterminal perovskite/c-Si and perovskite/CIGS tandem solar cells, respectively. Moreover, comparable tandem PCEs are observed for a broad range of perovskite bandgaps. For the first time, the robustness of the four-terminal tandem configuration with respect to variations in the perovskite bandgap for two state-of-the-art bottom solar cells is experimentally validated