Abstract
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 Fe
3
GeTe
2
(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.
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 Fe
GeTe
(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.
In this paper, the influence of reducing the thickness of the CIGSe absorber layer by bromine etching from 2.5
μm to 0.5
μm on electrical and optical solar cell properties is addressed. We observe a ...decrease in efficiency which is mainly caused by a reduced short circuit current, whereas the fill factor and the open circuit voltage are stable. Even without deliberate light trapping or anti-reflection coating, an efficiency of 10.3% is obtained for a 0.5
μm thick CIGSe absorber. A smoothing of the absorber surface is observed during the etching, its influence on the cell parameters will be discussed.
CIGSe absorber was etched in HBr/Br
2/H
2O to prepare defined thicknesses of CIGSe between 2.7 and 0.5
μm. We established a reproducible method of reducing the absorber thickness via chemical ...etching. We determine the dissolution kinetics rate of CIGSe using trace analysis by graphite furnace atomic absorption spectrometry of Ga and Cu. The roughness of the etching surface decreases during the first 500
nm of the etching to a steady state value of the root-mean-square roughness near 50
nm. X-ray photoelectron spectroscopy analyses demonstrate an etching process occurring with a constant chemical composition of the treated surface acidic bromine solutions provide a controlled chemical thinning process resulting in an almost flat surface and a very low superficial Se
0 enrichment.
Recently, a world-record efficiency of 22.6% was achieved by applying a RbF postdeposition treatment (PDT) on a Cu(In,Ga)Se2 (CIGSe) thin-film solar cell absorber surface. Here, we study the impact ...of this RbF-PDT on the electronic structure of the CIGSe surface and the CdS/CIGSe interface using ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS), as well as inverse photoemission spectroscopy (IPES). After RbF-PDT, we find a small downward shift of the band edges, while the surface band gap value itself is not affected. In addition, a further downward band bending in the CIGSe absorber is observed upon formation of the RbF-PDT CdS/CIGSe interface. We derive a flat conduction band alignment between the RbF-PDT CIGSe absorber and the CdS buffer, commensurate with the high efficiencies of solar cell devices prepared with RbF-PDT.
Indium sulphide has a high potential as a buffer layer material in Cu(In,Ga)Se
2 (CIGS) solar devices. In this work a metal organic vapour deposition (MOCVD) process was investigated for the indium ...sulphide deposition. Trimethyl-indium and t-butyl-thiol were applied as precursor sources. The films produced with different process conditions were characterised by scanning electron microscopy. We also present the first results of CIGS laboratory cells with an MOCVD indium sulphide buffer layer. The best device showed an efficiency of 12.3% (CdS reference
=
13.0%) at a deposition temperature of 300 °C and a deposition time of 20 min, combined with a 5 min post-annealing treatment at 200 °C in air.
