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

Single Skyrmion Generation via a Vertical Nanocontact in a 2D Magnet Based Heterostructure

Skyrmions have been well studied in chiral magnets and magnetic thin films due to their potential application in practical devices. Recently, monochiral skyrmions have been observed in two dimensional van der Waals magnets. Their atomically flat surfaces and capability to be stacked into heterostructures offer new prospects for skyrmion applications. However, the controlled local nucleation of skyrmions within these materials has yet to be realized. Here, we utilize real space X ray microscopy to investigate a heterostructure composed of the 2D ferromagnet Fe3GeTe2 FGT , an insulating hexagonal boron nitride layer, and a graphite top electrode. Upon a stepwise increase of the voltage applied between the graphite and FGT, a vertically conducting pathway can be formed. This nanocontact allows the tunable creation of individual skyrmions via single nanosecond pulses of low current density. Furthermore, time resolved magnetic imaging highlights the stability of the nanocontact, while our micromagnetic simulations reproduce the observed skyrmion nucleation proces

Skyrmion and skyrmionium formation in the two dimensional magnet Cr2Ge2Te6

The recently discovered 2D magnets represent versatile building blocks for spintronic devices. In particular, the out of plane 2D ferromagnets Fe3GeTe2 and Cr2Ge2Te6 CGT are attracting strong attention, owing to their ability to host topological spin textures. Among these, CGT is particularly interesting, as its semiconducting property could facilitate electric field control over the spin textures. Here, we systematically explore the magnetic phases of an exfoliated CGT flake with a thickness on the order of 50nm by scanning transmission x ray microscopy using three different measurement protocols. The domain periodicity was found to decrease with increasing temperature and decreasing flake thickness, the latter of which can be attributed to the relatively small magnetic anisotropy of CGT. Moreover, the magnetic phase diagram of CGT features a high temperature skyrmion phase pocket, and skyrmionium formation occurs upon zero field cooling. The sensitivity of the skyrmions to magnetic field changes indicates that dipolar interactions play a major role in stabilizing these magnetic spin texture

Photovoltaic system in progress: A survey of recent development

This paper provides a comprehensive update on photovoltaic (PV) technologies and the materials. In recent years, targeted research advancement has been made in the photovoltaic cell technologies to reduce cost and increase efficiency. Presently, several types of PV solar panels are commercially utilized and playing an important role in the market. Three generations of photovoltaic technologies are investigated and discussed; Crystalline Silicon Technology categorized as first generation of PV technology, Thin Film Technologies are second generation of PV technologies and Multi-junction Cells falls in the third generation PV technologies. However, Multi-junction Cells are still considered new and have not yet achieved commercialization status. The fundamental change observed among all generations has been how the semiconductor material is employed and the development associated with crystal structure. Silicon remains the prominent semiconductor within photovoltaic.</p

Seeding and Emergence of Composite Skyrmions in a van der Waals Magnet

Topological charge plays a significant role in a range of physical systems. In particular, observations of real space topological objects in magnetic materials have been largely limited to skyrmions states with a unitary topological charge. Recently, more exotic states with varying topology, such as antiskyrmions, merons, or bimerons and 3D states such as skyrmion strings, chiral bobbers, and hopfions, have been experimentally reported. Along these lines, the realization of states with higher order topology has the potential to open new avenues of research in topological magnetism and its spintronic applications. Here, real space imaging of such spin textures, including skyrmion, skyrmionium, skyrmion bag, and skyrmion sack states, observed in exfoliated flakes of the van der Waals magnet Fe3 amp; 8722;xGeTe2 FGT is reported. These composite skyrmions may emerge from seeded, loop like states condensed into the stripe domain structure, demonstrating the possibility to realize spin textures with arbitrary integer topological charge within exfoliated flakes of 2D magnets. The general nature of the formation mechanism motivates the search for composite skyrmion states in both well known and new magnetic materials, which may yet reveal an even richer spectrum of higher order topological object

Electron Beam Evaporated Nickel Oxide Hole Transport Layers for Perovskite Based Photovoltaics

High amp; 8208;quality charge carrier transport materials are of key importance for stable and efficient perovskite amp; 8208;based photovoltaics. This work reports on electron amp; 8208;beam amp; 8208;evaporated nickel oxide NiOx layers, resulting in stable power conversion efficiencies PCEs of up to 18.5 when integrated into solar cells employing inkjet amp; 8208;printed perovskite absorbers. By adding oxygen as a process gas and optimizing the layer thickness, transparent and efficient NiOx hole transport layers HTLs are fabricated, exhibiting an average absorptance of only 1 . The versatility of the material is demonstrated for different absorber compositions and deposition techniques. As another highlight of this work, all amp; 8208;evaporated perovskite solar cells employing an inorganic NiOx HTL are presented, achieving stable PCEs of up to 15.4 . Along with good PCEs, devices with electron amp; 8208;beam amp; 8208;evaporated NiOx show improved stability under realistic operating conditions with negligible degradation after 40 h of maximum power point tracking at 75 C. Additionally, a strong improvement in device stability under ultraviolet radiation is found if compared to conventional perovskite solar cell architectures employing other metal oxide charge transport layers e.g., titanium dioxide . Finally, an all amp; 8208;evaporated perovskite solar mini amp; 8208;module with a NiOx HTL is presented, reaching a PCE of 12.4 on an active device area of 2.3 cm

Highly productive manufacturing of CIS based large area modules

ABSTRACT Three independent European CIS manufacturers of different countries, a big player in glass coating industry, three universities and three research institutes work together in the EU project LARCIS in order to advance CIS manufacturing at high yields on glass substrates. The two main approaches for the realisation of enhanced module efficiencies at reduced costs are inline co evaporation of Cu In,Ga Se2 and electrodeposition of the CuInSe2 CIS precursor. Alternative back contacts such as ZrN and TiN with high optical reflection have been tested and molybdenum layers with enhanced conductivity for homogeneous electrodeposition on 30 x 30 cm2 have been DC sputtered. A chemical bath deposited Cd free ZnS based buffer has been applied on both CIS types resulting in high photocurrents and efficiencies which are at least as high as reference cells with CdS buffers. In parallel, an In2S3 buffer has been evaporated ex situ from powder with a certified maximum efficiency of 14.16 . Solar cells of up to 17.8 efficiency certified, with ARC were fabricated by using co evaporated multi stage CIGS from an inline reactor. CuIn Se,S 2 was electrodeposited homogeneously on substrate areas of 30 x 30 cm2. The mean efficiency of test cells distributed on this area was lt;8 gt;