The electronic doping mechanism of the Spiro-OMeTAD (2,2 ',7,7 '-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9 '-spirobifluorene) with LiTFSI (lithium bis(trifluoromethylsulfonyl)imide) and tBP (4-tert-Butylpyridine) has not been fully understood. Spiro-OMeTAD is a highly studied hole transport layer in solar cells and, especially, perovskite solar cells (PSCs). Its p-doping not only improves the hole transport characteristics and thus the photocurrent but also increases the band bending at the interface with the perovskite absorber and thus the cell photovoltage. A better understanding of the p-doping of Spiro-OMeTAD and its interface energetics with MAPI would contribute to optimization strategies for a better overall efficiency of the PSC. Until now, doping mechanisms were studied separately for liquid and thermal evaporation processing. It was impossible to pinpoint the similarities and differences between the two approaches. Using an integrated ultra-high vacuum cluster tool (DAISY-SOL), we prepared LiTFSI-doped Spiro-OMeTAD samples by spin-coating under an inert atmosphere and by thermal co-evaporation in a vacuum. Without contact with the atmosphere, the thin films were then characterized by photoelectron spectroscopy to deduce their electronic properties. It has been evidenced that with thermal co-evaporation, LiTFSI alone dopes the Spiro-OMeTAD layer, while for spin-coating, the additive tBP is required to prevent LiTFSI precipitation. Both processes give a more p-doped Spiro-OMeTAD layer by shifting its Fermi level toward the highest occupied molecular orbital (HOMO) at best by 0.65 eV. This results in a final energy difference between the Fermi level and the HOMO onset of 0.4 eV for the most p-doped sample. The co-evaporation process of LiTFSI and Spiro-OMeTAD was then used to perform interface experiments of doped Spiro-OMeTAD on MAPI and of Au on doped Spiro-OMeTAD to study a simplified solar cell structure SnO2 | MAPI | Spiro-OMeTAD | Au. Results confirm that the band alignment is suitable for electron blocking and hole extraction. Under light, a surface photovoltage of at least 0.65 eV is measured at the MAPI | Spiro-OMeTAD interface, making it the functional key interface. These interface experiments provide a not only detailed but also quantitative picture of the band alignment both in the dark and in operation under illumination under open circuit conditions.

The chemical selectivity and faradaic efficiency of high-index Cu facets for the CO 2 reduction reaction (CO 2 RR) is investigated. More specifically, shape-controlled nanoparticles enclosed by Cu {hk0} facets are fabricated using Cu multilayer deposition at three distinct layer thicknesses on the surface facets of Au truncated ditetragonal nanoprisms (Au DTPs). Au DTPs are shapes enclosed by 12 high-index {310} facets. Facet angle analysis confirms DTP geometry. Elemental mapping analysis shows Cu surface layers are uniformly distributed on the Au {310} facets of the DTPs. The 7 nm Au@Cu DTPs high-index {hk0} facets exhibit a CH 4  : CO product ratio of almost 10 : 1 compared to a 1 : 1 ratio for the reference 7 nm Au@Cu nanoparticles (NPs). Operando Fourier transform infrared spectroscopy spectra disclose reactive adsorbed *CO as the main intermediate, whereas CO stripping experiments reveal the high-index facets enhance the *CO formation followed by rapid desorption or hydrogenation.

We report on the structural, electric and magnetic properties of (NixCo1−x)B ferromagnetic nanotubes, displaying azimuthal magnetization. The tubes are fabricated using electroless plating in polycarbonate porous templates, with lengths of several tens of micrometers, diameters from 100 nm to 500 nm and wall thicknesses from 10 nm to 80 nm. The resistivity is ∼1.5×10−6Ω m, and the anisotropic magnetoresistance (AMR) of 0.2 to 0.3%, one order of magnitude larger (resp. smaller) than in the bulk material, which we attribute to the resistance at grain boundaries. We determined the azimuthal anisotropy field from M(H) AMR loops of single tubes contacted electrically. Its magnitude is around 10 mT, and tends to increase with the tube wall thickness, as well as the Co content. However, surprisingly it does not dependent much on the diameter nor on the curvature.

Efficient base-modulated product selectivity in the aqueous-phase Ru/C-catalyzed reductive amination of 1,6-hexanediol (HDO) was reported by performing the reaction at mild conditions (463 K, 25 bar H2). High selectivity of amines could be controlled by the addition of different bases; for example, Cs2CO3 addition gave a high yield of 6-amino-1-hexanol (AH, 26%). However, the addition of Ba(OH)2 resulted in the formation of high yield of secondary amination products, hexamethylenedi-amine (HMDA, 34%) and azepane (26%). The hydroxide base, especially Ba(OH)2, aids in the initial conversion of HDO to AH by significantly decreasing the apparent activation energy from 68 to 48 kJ mol-1. A closer analysis of the formation of secondary products (azepane and HMDA) revealed a faster reaction between NH3 and the carbonyl-containing intermediate by the addition of Ba(OH)2 into the reaction solution.

Vacuum‐based deposition of optoelectronic thin films has a long‐standing history. However, in the field of perovskite‐based photovoltaics, these techniques are still not as advanced as their solution‐based counterparts. Although high‐efficiency vacuum‐based perovskite solar cells reaching power conversion efficiencies (PCEs) above 20% are reported, the number of studies on the underlying physical and chemical mechanism of the co‐evaporation of lead iodide and methylammonium iodide is low. In this study, the impact of one of the most crucial process parameters in vacuum processes—the substrate material—is studied. It is shown that not only the morphology of the co‐evaporated perovskite thin films is significantly influenced by the surface polarity of the substrate material, but also the incorporation of the organic compound into the perovskite framework. Based on these studies, a selection guide for suitable substrate materials for efficient co‐evaporated perovskite thin films is derived. This selection guide points out that the organic vacuum‐processable hole transport material 2,2″,7,7″‐tetra( N , N ‐di‐p‐tolyl)amino‐9,9‐spirobifluorene is an ideal candidate for the fabrication of efficient all‐evaporated perovskite solar cells, demonstrating PCEs above 19%. Furthermore, building on the insights into the formation of the perovskite thin films on different substrate materials, a basic crystallization model for co‐evaporated perovskite thin films is suggested.

One of the great challenges of hybrid organic-inorganic perovskite photovoltaics is the material's stability at elevated temperatures. Over the past years, significant progress has been achieved in the field by compositional engineering of perovskite semiconductors, e.g., using multiple-cation perovskites. However, given the large variety of device architectures and nonstandardized measurement protocols, a conclusive comparison of the intrinsic thermal stability of different perovskite compositions is missing. In this work, we systematically investigate the role of cation composition on the thermal stability of perovskite thin films. The cations in focus of this study are methylammonium (MA), formamidinium (FA), cesium, and the most common mixtures thereof. We compare the thermal degradation of these perovskite thin films in terms of decomposition, optical losses, and optoelectronic changes when stressed at 85 °C for a prolonged time. Finally, we demonstrate the effect of thermal stress on perovskite thin films with respect to their performance in solar cells. We show that all investigated perovskite thin films show signs of degradation under thermal stress, though the decomposition is more pronounced in methylammonium-based perovskite thin films, whereas the stoichiometry in methylammonium-free formamidinium lead iodide (FAPbI3) and formamidinium cesium lead iodide (FACsPbI3) thin films is much more stable. We identify compositions of formamidinium and cesium to result in the most stable perovskite compositions with respect to thermal stress, demonstrating remarkable stability with no decline in power conversion efficiency when stressed at 85 °C for 1000 h. Thereby, our study contributes to the ongoing quest of identifying the most stable perovskite compositions for commercial application.

In this study, dual-phase membranes 60 wt % Ce0.8M0.2O2-delta (M = La, Pr, Nd, Sm, Gd) - 40 wt % La0.5Sr0.5Fe0.8Cu0.2O3-delta (CMO-LSFCO) were prepared via a combination of EDTA-citric acid complexing sol-gel and mechanical mixture method. Their chemical compatibility, CO2 tolerance, oxygen permeability, conductivity, and long-term regenerative durability regarding the phase structure and composition were systematically studied. Among the studied CMO-LSCFO dual-phase membranes, CGO-LSFCO shows the highest oxygen permeability under air/He and air/CO2 gradients, which can be associated with the small particle size and high electronic conductivity of the CGO phase resulting in a good percolation with different transfer paths based on the correlations between membrane material characterization and oxygen permeability. The comprehensive comparative study presented in this work identifies the critical factors influencing the oxygen permeability, which may provide guidelines for designing further high performance dual-phase oxygen transport membranes.

Iodide migration causes degradation of the perovskite solar cells. Here, we observe the direct migration of iodide into the hole-transport layer in a device. We demonstrate that ultrathin room temperature atomic layer-deposited Al2O3 on the perovskite surface very effectively hinders the migration The perovskite-Al2O3 interface enables charge transfer across the Al2O3 layer in the solar cells, without causing any drastic changes in the properties of the perovskite absorber Furthermore, it helps to preserve the initial properties of the perovskite film during exposure to light and air under real operating conditions, and thus, improves the stability of the solar cells. The ultrathin Al2O3 layer deposited at room temperature significantly increases the lifetime of the perovskite solar cells, and we hope this may be a step toward the mass production of stable devices.

Electroless plating is a powerful tool in nanofabrication and is available for many of the noble transition metals. There is, however, a striking lack of electroless plating procedures for the rarer platinum-group metals. In this work, two plating baths for nanoscale iridium coatings are developed and their conformality and nanofabrication potential are showcased by coating ion-track-etched polycarbonate membranes, creating Ir nanotubes in the process. Both plating solutions yield morphologically different deposits, indicating that the microstructure of the film can be tuned by adjusting the composition of the plating bath. The catalytic performance of the deposited materials is investigated by using membrane-embedded nanotubes as catalysts for the reduction of 4-nitrophenol and methyl orange by borohydride, showing remarkable activity and stability. Operation in flow-through configuration, in which the metallized membrane is implemented as a microreactor greatly enhances the interaction with the catalyst surface, considerably increasing product yield. The results highlight the potential of Ir nanoplating for realizing sophisticated nanostructures and heterogeneous catalysts, but also illustrate the intricacies related to the complex chemistry of electroless Ir plating baths.

Abstract An upscalable chemical vapor deposition setup has been built‐up and employed in producing methylammonium lead iodide (MAPI) thin film perovskite solar cells, leading to a maximum efficiency of 12.9%. The method makes use of methylamine gas and hydrogen iodide gas to transform a predeposited layer of lead(II)iodide (PbI2) into MAPI. Although the reaction mechanism includes the intermediate phases lead oxide (PbO) and lead hydroxide (Pb(OH)2), indicated at least on the surface of the samples by XPS, neither species could be observed in XRD measurements of the stepwise reaction, which show a mixture of highly oriented cubic and tetragonal MAPI perovskite lattice systems.

The surface, interface, and bulk properties are a few of the most critical factors that influence the performance of perovskite solar cells. The photoelectron spectroscopy (PES) is used as a technique to analyze these properties. However, the information depth of PES is limited to 10-20 nm, which makes it not suitable to study the complete devices, which have a thickness of ∼1 μm. Here, we introduce a novel and simple technique of PES on a tapered cross section (TCS-PES). It provides both lateral and vertical resolutions compared to the conventional PES so that it is suitable to study a complete perovskite solar cell. It offers many benefits over conventional PES methods such as the chemical composition in the micrometer scale from the surface to the bulk and the electronic properties at the multiple interfaces. The chemical natures of different layers of the perovskite-based solar cells [(FAPbI3)0.85(MAPbBr3)0.15] can be identified precisely for the first time using the TCS-PES method. We found that the perovskite layer has higher iodine concentration at the Spiro/perovskite interface and higher bromine concentration at the TiO2/perovskite interface. UPS measurements on the tapered cross section revealed that the perovskite is n-type, and the solar cell studied here is a p-n-n structure type device. The unique possibilities to analyze the complete solar cell by XPS and UPS allow us to estimate the band bending in a working solar cell. Moreover, this technique can further be used to study the device under operating conditions, and it can be applied in other solid-state devices like solid electrolyte Li-ion batteries, LEDs, or photoelectrodes.

The purpose of this article is twofold. On the one hand the method of spacial resolved photoemission spectroscopy on small angle tapered cross-sections (TCS) of complete devices is introduced to analyze simultaneously the chemical and electronic structure. On the other hand, a specific working principle of the analyzed cell type is revealed. Solar cells of 18% efficiency are prepared from a single precursor (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 with excess of 15% PbI 2 . It is shown that TCS-phototoelectron spectroscopy allows to determine the chemical composition as well as the potential distribution across the full device in the dark and in operation. The energy converting contact is the hole extraction back contact. Interestingly the photopotential in the analyzed cell type is predominantly created within the hole extraction layer and not in the n-doped perovskite absorber. With the addition of measured core level to valence band maximum positions of the respective layers, TCS line scans lead to the band diagram for the full device. In addition, depth variations of the chemical composition are found: the bromide concentration increases while the iodide concentration is reduced near and within the mesoporous TiO 2 layer.

High power conversion efficiency (PCE) perovskite solar cells (PSCs) rely on optimal alignment of the energy bands between the perovskite absorber and the adjacent charge extraction layers. However, since most of the materials and devices of high performance are prepared by solution-based techniques, a deposition of films with thicknesses of a few nanometers and therefore a detailed analysis of surface and interface properties remains difficult. To identify the respective photoactive interfaces, photoelectron spectroscopy measurements are performed on device stacks of methylammonium-lead-iodide (MAPI)-based PSCs in classical and inverted architectures in the dark and under illumination at open-circuit conditions. The analysis shows that vacuum-deposited MAPI perovskite absorber layers are n-type, independent of the architecture and of the charge transport layer that it is deposited on (n-type SnO(2)or p-type NiOx). It is found that the majority of the photovoltage is formed at the n-MAPI/p-HEL (hole extraction layer) junction for both architectures, highlighting the importance of this interface for further improvement of the photovoltage and therefore also the PCE. Finally, an experimentally derived band diagram of the completed devices for the dark and the illuminated case is presented.

Nanostructured silver stands out among other plasmonic materials because its optical losses are the lowest of all metals. However, nanostructured silver rapidly degrades under ambient conditions, preventing its direct use in most plasmonic applications. Here, a facile and robust method for the preparation of highly stable nanostructured silver morphologies is introduced. 3D nanostructured gyroid networks are fabricated through electrodeposition into voided, self-assembled triblock terpolymer scaffolds. Exposure to an argon plasma degraded the polymer and stabilized the silver nanostructure for many weeks, even in high humidity and under high-dose UV irradiation. This stabilization protocol enables the robust manufacture of low-loss silver nanostructures for a wide range of plasmonic applications.

In the urge of designing noble metal-free and sustainable electrocatalysts for oxygen evolution reaction (OER), herein, a mineral Digenite Cu9S5 has been prepared from a molecular copper(I) precursor, [{(PyHS)(2)Cu-I(PyHS)}(2)](OTf)(2) (1), and utilized as an anode material in electrocatalytic OER for the first time. A hot injection of 1 yielded a pure phase and highly crystalline Cu9S5, which was then electrophoretically deposited (EPD) on a highly conducting nickel foam (NF) substrate. When assessed as an electrode for OER, the Cu9S5/NF displayed an overpotential of merely 298 +/- 3 mV at a current density of 10 mA cm(-2) in alkaline media. The overpotential recorded here supersedes the value obtained for the best reported Cu-based as well as the benchmark precious-metal-based RuO2 and IrO2 electrocatalysts. In addition, the choronoamperometric OER indicated the superior stability of Cu9S5/NF, rendering its suitability as the sustainable anode material for practical feasibility. The excellent catalytic activity of Cu9S5 can be attributed to the formation of a crystalline CuO overlayer on the conductive Cu9S5 that behaves as active species to facilitate OER. This study delivers a distinct molecular precursor approach to produce highly active copper-based catalysts that could be used as an efficient and durable OER electro(pre)catalysts relying on non-precious metals.

We have studied the electronic structure of CH3NH3PbI3 (MAPI) and CH3NH3SnI3 (MASI) perovskite films by performing X-ray photoelectron spectroscopy (XPS) measurements on in situ grown perovskite films.

Using the one‐step flash evaporation technique, it is possible to deposit a film of methylammonium tin iodide (MASI, CH3NH3SnI3) from the solid perovskite powder that is prepared by a mechanochemical synthesis, without the use of any solvents. The source material and the film are characterized by X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD). The XPS measurements show that the MASI film is stoichiometric and is a p‐type material with the Fermi level of 0.4 eV above the valence band maximum (VBM) and a bandgap of 1.3 eV. The XRD pattern of the film reveals the formation of MASI perovskite of high purity, crystallizing with pseudo‐cubic symmetry, having the lattice parameters a ≈ c = 6.239(8) Å.

The purpose of this article is twofold. On the one hand the method of spacial resolved photoemission spectroscopy on small angle tapered cross-sections (TCS) of complete devices is introduced to analyze simultaneously the chemical and electronic structure. On the other hand, a specific working principle of the analyzed cell type is revealed. Solar cells of 18% efficiency are prepared from a single precursor (FAPbI(3))(0.85)(MAPbBr(3))(0.15) with excess of 15% PbI2. It is shown that TCS-phototoelectron spectroscopy allows to determine the chemical composition as well as the potential distribution across the full device in the dark and in operation. The energy converting contact is the hole extraction back contact. Interestingly the photopotential in the analyzed cell type is predominantly created within the hole extraction layer and not in the n-doped perovskite absorber. With the addition of measured core level to valence band maximum positions of the respective layers, TCS line scans lead to the band diagram for the full device. In addition, depth variations of the chemical composition are found: the bromide concentration increases while the iodide concentration is reduced near and within the mesoporous TiO2 layer.