Sebastian Siol

Empa - Swiss Federal Laboratories for Materials Science and Technology | Empa · Department of Advanced Materials and Surfaces

Energy band alignments at heterointerfaces play a crucial role in defining the functionality of semiconductor devices, yet the search for material combinations with suitable band alignments remains a challenge for numerous applications. In this work we demonstrate how changes in deposition conditions can dramatically influence the functional proper...

Combinatorial techniques can be utilized to accelerate in situ interface studies. This is demonstrated by investigating the prototypical Sb2Se3/ZnS heterojunction. Film thickness gradients on the substrate are used to minimize the required number of depositions and transfers. Other synthesis parameters such as the substrate temperature or film comp...

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively....

The ability of a material to adopt multiple structures, known as polymorphism, is a fascinating natural phenomenon. Various polymorphs with unusual properties are routinely synthesized by compression under positive pressure. However , changing a material's structure by applying tension under negative pressure is much more difficult. We show how neg...

The increasing demand for novel inorganic materials with targeted functionality motivates moving beyond the area of traditionally explored near‐equilibrium materials by incorporating metastable phase space into materials design and discovery. It has recently been shown that heterostructural semiconductor alloys can exhibit increased regions of meta...

Resolving Chemical States of Sn‐Based Perovskites: In article 2201828, Alexander Wieczorek, Sebastian Siol, and colleagues demonstrate how Auger parameter analysis enables more reliable chemical state analysis of Sn‐based perovskites. Through systematic compositional variation a high sensitivity of this parameter on the X‐site composition and oxid...

The long search for nontoxic alternatives to lead halide perovskites (LHPs) has shown that some compelling properties of LHPs, such as low effective masses of carriers, can only be attained in their closest Sn(II) and Ge(II) analogues, despite their tendency toward oxidation. Judicious choice of chemistry allowed formamidinium tin iodide (FASnI3) t...

Many technologies require highly-oriented and textured functional thin films. The most common synthe-sis approaches use on-axis sputter geometries. However, in some scenarios, on-axis sputtering is not feasible. During ionized physical vapor deposition (PVD), in contrast to conventional PVD, the film-forming species can be accelerated onto the grow...

Reliable chemical state analysis of Sn semiconductors by XPS is hindered by the marginal observed binding energy shift in the Sn 3d region. For hybrid Sn‐based perovskites especially, errors associated with charge referencing can easily exceed chemistry‐related shifts. Studies based on the modified Auger parameter α ′ provide a suitable alternative...

Perovskite Solar Cells In article number 2202438, Cong Chen, Dewei Zhao, Fan Fu, and co‐workers report 15.1% flexible near‐infrared transparent wide‐bandgap (1.77 eV) perovskite solar cells with a low open‐circuit voltage–deficit of 480 mV. When paired with flexible, narrow‐bandgap (1.24 eV) perovskite solar cells, they demonstrate a 23.8% flexible...

Photoelectron spectroscopy is an important tool for the development of new materials. However, especially for nitride semiconductors, the formation of surface oxides, surface band bending as well as the lack of a suitable charge reference often prevent a robust analysis. Here, we perform a comprehensive chemical state analysis of the Zn-V-N phase s...

Among various types of perovskite‐based tandem solar cells (TSCs), all‐perovskite TSCs are of particular attractiveness for building‐ and vehicle‐integrated photovoltaics, or space energy areas as they can be fabricated on flexible and lightweight substrates with a very high power‐to‐weight ratio. However, the efficiency of flexible all‐perovskite...

Reliable chemical state analysis of Sn semiconductors by XPS is hindered by the marginal observed shift in the Sn 3d region. For hybrid Sn-based perovskites especially, errors associated with charge referencing can easily exceed chemistry-related shifts. Studies based on the modified Auger parameter ${\alpha}'$ provide a suitable alternative and ha...

Among various types of perovskite-based tandem solar cells (TSCs), all-perovskite TSCs are of particular attractiveness for building- and vehicle-integrated photovoltaics, or space energy areas as they can be fabricated on flexible and lightweight substrates with a very high power-to-weight ratio. However, the efficiency of flexible all-perovskite...

Nucleation and early growth of Li metal is critical to the performance of anode-free solid-state batteries. We report the use of amorphous carbon deposited by direct current magnetron sputtering as an intermediate layer between the Cu current collector and the Lipon solid electrolyte. The density, conductivity, and microstructure of the carbon inte...

Sb2Se3 has emerged as an important photoelectrochemical (PEC) and photovoltaic (PV) material due to its rapid rise in photoconversion efficiencies. However, Sb2Se3 has a complex defect chemistry, which reduces the maximum photovoltage. Thus, it is important to understand these defects and develop defect passivation strategies in Sb2Se3. A comprehen...

Photoelectron spectroscopy is an important tool for the development of new materials. However, especially for nitride semiconductors, the formation of surface oxides, surface band bending as well as the lack of a suitable charge reference often prevent a robust analysis. Here, we perform a comprehensive chemical state analysis of the Zn-V-N phase s...

Efficient catalytic oxidative C–H activation of organic substrates remains an important challenge in synthetic chemistry. Here, we show that the combination of a transition metal catalyst, surface immobilisation and an electrochemical potential provide a promising approach to effecting these transformations in aqueous solution. A ruthenium-based mo...

Computationally guided high-throughput synthesis is used to explore the Zn-V-N phase space, resulting in the synthesis of a novel ternary nitride Zn$_2$VN$_3$. Following a combinatorial PVD screening, we isolate the phase and synthesize polycrystalline Zn$_2$VN$_3$ thin films on conventional borosilicate glass substrates. In addition, we demonstrat...

The properties and thermal stability of thin films and nano-multilayers (NMLs) are generally governed by the in-depth stress (strain) gradients rather than the average stress state. The effect of strain gradient variation in Cu/W NMLs on the thermal stability between 400 – 800 °C was investigated. The strain distribution in the NML stacks was varie...

Cu 2 S is a promising solar energy conversion material owing to its good optical properties, elemental earth abundance and low cost. However, simple and cheap methods to prepare phase‐pure and photo‐active Cu 2 S thin films are lacking. Here, we present a cost‐effective and high‐throughput method that consists of dissolving high‐purity commercial C...

Hard X-ray photoelectron spectroscopy (HAXPES) is establishing itself as an essential technique for the characterisation of materials. The number of specialised photoelectron spectroscopy techniques making use of hard X-rays is steadily increasing and ever more complex experimental designs enable truly transformative insights into the chemical, ele...

p>Sb₂Se₃has emerged as an important photoelectrochemical (PEC) and photovoltaic (PV) material due to its rapid rise in photoconversion efficiencies. However, despite its binary nature, Sb₂Se₃has a complex defect chemistry, which reduces the maximum photovoltage that can be obtained. Thus, it is importan...

Sb 2 Se 3 has emerged as an important photoelectrochemical (PEC) and photovoltaic (PV) material due to its rapid rise in photoconversion efficiencies. However, despite its binary nature, Sb 2 Se 3 has a complex defect chemistry, which reduces the maximum photovoltage that can be obtained. Thus, it is important to understand these defects and to dev...

Antimony sulfide (Sb2S3) is a promising light-absorbing semiconductor for photovoltaic applications, though it remains vastly unexplored for photoelectrochemical water splitting. Sb2S3 was synthesized by a simple sulfurization of electrodeposited antimony metal at relatively low temperatures (240–300 °C) with elemental sulfur. Using a TiO2 buffer l...

Antimony sulfide (Sb2S3) is a promising light absorbing semiconductor for photovoltaic applications, though it remains vastly unexplored for photoelectrochemical water splitting. Sb2S3 was synthesized by a simple sulfurization of electrodeposited antimony metal at relatively low temperatures (240-300°C) with elemental sulfur. Using a TiO2 buffer la...

Water oxidation is the bottleneck reaction for overall water splitting as a direct and promising strategy toward clean fuels. However, the development of robust and affordable heterogeneous water oxidation catalysts remains challenging, especially with respect to the wide parameter space of synthesis and resulting material properties. Oxide catalys...

p>Antimony sulfide (Sb₂S₃) is a promising light absorbing semiconductor for photovoltaic applications, though it remains vastly unexplored for photoelectrochemical water splitting. Sb₂S₃ was synthesized by a simple sulfurization of electrodeposited antimony metal at relatively low temperatures (240-300°C)...

The stability, reactivity and functionality of modern nanostructured and nano-architectured materials, like nano-multilayers (NMLs) and nano-composites (NCs), are generally ruled by fast short-circuit diffusion of atoms along internal interfaces, such as phase and grain boundaries (GBs), at relatively low temperatures. Residual stresses can have a...

The greater information depth provided in hard X‐ray photoelectron spectroscopy (HAXPES) enables nondestructive analyses of the chemistry and electronic structure of buried interfaces. Moreover, for industrially relevant elements like Al, Si, and Ti, the combined access to the Al 1s, Si 1s, or Ti 1s photoelectron line and its associated Al KLL, Si...

The Front Cover shows a two‐seater airplane emerging from a thin cloud up in the sky on a sunny day. In their Full Paper, H. T. Luk et al. demonstrate a serial catalyst arrangement comprising copper and iron supported on carbon nanofibers and a zeolite, represented by the two pilots, that breach together a new level in the synthesis of higher alcoh...

TiO2 and WO3 are two of the most important earth-abundant electronic materials with applications in countless industries. Recently alloys of WO3 and TiO2 have been investigated leading to improvements of key performance indicators for a variety of applications ranging from photo-electrochemical water splitting to electrochromic smart windows. These...

A comprehensive understanding of the oxidation of Cu thin films in the low-temperature regime is of fundamental interest and particularly relevant for applications in the fields of micro- and nanoelectronics, sensors, catalysis, and solar cells. The current study reports on the oxidation kinetics of PVD grown Cu thin films (20–150 nm thick) and the...

Materials with crystal structures containing tetrahedral motifs are preferable for optoelectronic applications because they often have direct band gaps and low electron effective masses. However, crystal structures of manganese chalcogenides typically contain octahedral motifs, such as in rock salt (RS) MnS and MnSe materials. Here, we experimental...

Converting syngas obtained from renewable or abundant feedstocks into higher alcohols (HA) is a potentially more sustainable route to these important chemicals and fuels than industrial technologies, but lacks a performing catalytic process to reach commercialization. Here, we show that moderate CO 2 amounts (R = CO 2 /(CO+CO 2 ) = 0.12) in the fee...

Metastable inorganic materials with unique properties are important in many practical applications, but their synthesis is often challenging. In physics, epitaxial stabilization, also known as pseudomorphic growth, is used to synthesize metastable polymorphs, but usually only as very thin films and on expensive single-crystal substrates. In chemist...

The greater information depth provided in Hard X-ray Photoelectron Spectroscopy (HAXPES) enables non-destructive analyses of the chemistry and electronic structure of buried interfaces. Moreover, for industrially relevant elements like Al, Si and Ti, the combined access to the Al 1s, Si 1s or Ti 1s photoelectron line and its associated Al KLL, Si K...

The development of efficient, stable, and economic water oxidation catalysts (WOCs) is a forefront topic of sustainable energy research. We newly present a comprehensive three-step approach to systematically investigate challenging relationships among preparative history, properties, and performance in heterogeneous WOCs. To this end, we studied (1...

TiO2 and WO3 are two of the most important earth-abundant electronic materials with applications in countless industries. Recently alloys of WO3 and TiO2 have been investigated leading to improvements of key performance indicators for a variety of applications ranging from photo-electrochemical water splitting to electrochromic smart windows. These...

Zinc tin nitride (ZnSnN 2) is an emerging ternary nitride semiconductor studied for applications in solar cells, light-emitting diodes, and other optoelectronic devices. For all of these applications, the charge carrier mobility is an important property. However, the dominant electron scattering mechanisms in ZnSnN 2 are unclear, especially in the...

Thermal treatment of nano-multilayers (NMLs) constituted of alternating immiscible metals, like W and Cu, can evolve in a nanocomposite (NC) with tailored mechanical, electrical and/or thermal properties. The NML-to-NC transformation can result in unique material properties of the resulting NC, which can hardly be achieved by conventional composite...

A key challenge for photoelectrochemical water splitting is that high performance semiconductors are not stable in aqueous electrolytes, necessitating corrosion protection layers such as TiO2. In the best case, the protection layer would also serve as the heterojunction partner, minimizing complexity and thereby cost. However, the bands of most hig...

TiO2 and WO3 are two of the most important, industrially relevant earth-abundant oxides. While both materials show complementary functionality, and are promising candidates for similar types of applications such as catalysis, sensor technology and energy conversion, their chemical stability in reactive environments differs remarkably. In this study...

Semiconductor-based solar energy conversion devices are often multilayer structures with each layer serving a distinct purpose towards generating an efficient and stable device. In water splitting, the use of atomic layer deposited TiO2 (ALD-TiO2) layers enables the stable operation of materials that would normally photocorrode in the aqueous elect...

Anchored molecular catalysts provide a good step towards bridging the gap between homogeneous and heterogeneous catalysis. However, applications in an aqueous environment pose a serious challenge to anchoring groups in terms of stability. Ultrathin overlayers embedding these catalysts on the surface using atomic layer deposition (ALD) are an elegan...

The identification of an effective copper-iron catalyst for the direct conversion of synthesis gas into higher alcohols is hindered by the low solubility limit of Cu in Fe and the limited understanding of structural and electronic descriptors in such multicomponent systems. Here, commercial carbonaceous carriers are shown to produce an efficient ma...

Substrate reuse offers a promising route toward enabling high-efficiency III–V solar cells to become cost-competitive for one-sun terrestrial applications. In this study, Ge films were spalled using an electroplated Ni stressor layer, and the fracture surface was characterized. Initial heteroepitaxial GaAs films grown on spalled Ge substrates by hy...

Alloying of semiconductors with similar crystal structures is often used to fine-tune materials properties for optoelectronic applications. However, examples of semiconductor alloys between compounds with two different crystal structures, where properties are changing dramatically as a function of composition, are much rarer. Even more unusual are...

An understanding of the heterostructural implications on alloying in the aluminum nitride-scandium nitride system (Al1−xScxN) can highlight opportunities and design principles for enhancing desired material properties by leveraging nonequilibrium states. The fundamental thermodynamics, and therefore composition- and structure-dependent mechanisms,...

An important challenge in the development of optoelectronic devices for energy conversion applications is the search for suitable p-type contact materials. For example, p-type MnTe would be a promising alternative back contact to due to their chemical compatibility, but at normal conditions it has too narrow band gap due to octahedrally coordinated...

As high-throughput combinatorial experimental methods become more common, the technical challenge is shifting from producing materials to dealing with increasingly large datasets. One of the most important metrics to determine suitability of semiconductor materials for various applications is the band gap. This paper discusses automated algorithms...

The Cover Feature shows the generation of the active titania phase embedded into a silicon carbide matrix to develop an efficient catalyst for the selective activation of C–H bonds. This strategy is critical for the establishment of new catalytic technologies for the exploitation of abundant natural gas reserves as potential feedstock for chemicals...

The room-temperature formation of bismuth oxycarbonate (Bi2O2CO3) from Bi2O3 in sodium carbonate buffer was investigated with in situ powder X-ray diffraction (PXRD) in combination with electron microscopy and vibrational spectroscopy. Time-resolved PXRD measurements indicate a pronounced and rather complex pH dependence of the reaction mechanism....

The development of industrially-viable heterogeneous catalysts for higher alcohols (HA) synthesis via direct syngas conversion is hindered by the limited understanding of structural and electronic descriptors of their performance. Here, K-promoted CoMo(5 wt.%)-based catalysts were investigated to shed light onto property-function relations. Evaluat...

Alkane oxyhalogenation has emerged as an attractive catalytic route for selective natural gas functionalization to important commodity chemicals, such as methyl halides or olefins. However, few systems have been disclosed to be active and selective in these reactions. Here, we identify a novel and highly efficient TiC-SiC composite for methane and...

The poor stability of high efficiency photoabsorber materials in aqueous media is one factor holding back the realization of photoelectrochemical (PEC) water splitting for large scale, practical solar fuels generation. Here, we demonstrate that highly efficient thin film Sb2Se3–fabricated by a simple, low temperature selenization of electrodeposite...

Optically transparent materials with p-type electrical conductivity can facilitate the development of transparent electronics, and improve the efficiency of photovoltaic solar cells. Sulfide materials represent an interesting alternative to oxides for these applications due to better hole transport properties. Here, transparent and conductive Ba-Cu...

We grow and kinetically stabilize the isotropic rocksalt phase of SnSe thin films by alloying SnSe with CaSe. Thin polycrystalline films of the metastable heterostructural alloy Sn1-xCaxSe are synthesized by pulsed laser deposition on amorphous SiO2 over the entire composition range 0 < x < 1. We observe the theoretically-predicted, composition-dri...

Direct solution coating technique has emerged as a promising economically viable process for earth abundant chalcogenide absorber materials for photovoltaic applications. Here, direct ethanol based dip coating of earth abundant Cu2NiSnS4 (CNTS) films on soda lime glass (SLG), molybdenum coated glass (Mo), and fluorine doped tin oxide coated glass (...

The controlled decomposition of metastable alloys is an attractive route to form nanostructured thermoelectric materials with reduced thermal conductivity. The ternary SnTe-MnTe and SnTe–SnSe heterostructural alloys have been demonstrated as promising materials for thermoelectric applications. In this work, the quaternary Sn1-yMnyTe1-xSex phase spa...

Perovskite solar cells have made tremendous progress using laboratory-scale spin-coating methods in the past few years owing to advances in controls of perovskite film deposition. However, devices made via scalable methods are still lagging behind state-of-the-art spin-coated devices because of the complicated nature of perovskite crystallization f...

Recently, there has been an explosive growth in research based on hybrid lead-halide perovskites for photovoltaics owing to rapid improvements in efficiency. The advent of these materials for solar applications has led to widespread interest in understanding the key enabling properties of these materials. This has resulted in renewed interest in re...