Perovskite solar cells have shown a rapid increase of performance and overcome the threshold of 20% power conversion efficiency (PCE). The main issues hampering commercialization are the lack of ...deposition methods for large areas, missing long-term device stability and the toxicity of the commonly used Pb-based compounds. In this work, we present a novel chemical vapor deposition (CVD) process for Pb-free air-stable methylammonium bismuth iodide (MBI) layers, which enables large-area production employing close-coupled showerhead technology. We demonstrate the influence of precursor rates on the layer morphology as well as on the optical and crystallographic properties. The impact of substrate temperature and layer thickness on the morphology of MBI crystallites is discussed. We obtain smooth layers with lateral crystallite sizes up to 500 nm. Moreover, the application of CVD-processed MBI layers in non-inverted perovskite solar cells is presented.
The effect of different carbon doping techniques on the dynamic behavior of GaN-on-Si buffer was investigated. Intentional doping using a hydrocarbon precursor was compared with the more common ...autodoping technique. Breakdown and dynamic behavior of processed devices indicate that extrinsic carbon doping delivers better dynamic properties for the same blocking voltage capabilities. Modeling and simulations have revealed that charge transport across the GaN buffer is the main limiting factor during the buffer discharge process.
CsPbBr
3
represents a highly attractive material for perovskite light-emitting diodes (PeLEDs) in the green spectral range. However, the lack of deposition tools for reproducible and scalable growth ...of perovskite films is one of the major obstacles hindering PeLED commercialization. Here, we employ the highly scalable showerhead-assisted chemical vapor deposition (CVD) method to produce uniform pinhole-free CsPbBr
3
films for PeLED application. The precursors CsBr and PbBr
2
are evaporated under low vacuum in N
2
carrier gas. By adjusting the PbBr
2
sublimation temperature, process conditions for CsBr-rich, stoichiometric, and PbBr
2
-rich CsPbBr
3
layer growth have been developed. A substrate temperature of 160 °C enables direct growth of these CsPbBr
3
films on a polymeric hole transport layer (HTL), finally yielding PeLEDs with a maximum luminance of 125 cd/m
2
. Although the device efficiency still lags behind solution-processed counterparts, our approach presents the first demonstration of PeLEDs containing CsPbBr
3
films processed in a perovskite showerhead-assisted CVD reactor.
Graphic abstract
AlN layers were grown by metalorganic vapor-phase epitaxy at high temperatures up to 1500
°C. Nucleation layer growth parameters and flow conditions before nucleation were changed and the effect on ...the AlN layer grown on top was studied. Structural analysis performed by high-resolution X-ray diffractometry and transmission electron microscopy showed that pregrowth conditions affect the material quality drastically. The best structural quality as indicated by a screw (including mixed) dislocation density of 8×10
8
cm
−2, together with smooth surface morphology was found to result from simultaneous switching on of ammonia and TMAl at the beginning of nucleation layer growth.
(Left) Excellent agreement of simulated and measured luminance distribution. (Right) Two efficient techniques for the enhancement of luminance distribution. Display omitted
•Excellent agreement of ...simulation and measurement.•Demonstration, analysis and measurement of different design approaches for OLED with grid lines.•Variation of grid element shape is not the best way to find optimal grid structure.•Variation of grid spacing and grid line width is the best way to optimize grid structure.•Proof of dependence between different enhancement techniques by simulation.
Luminance homogeneity is an important aspect for large-area (>1cm2) organic light emitting diodes (OLED). Especially, high sheet resistances of transparent contacts lead to a significant brightness inhomogeneity caused by a drop of local potential difference. Therefore the implementation of thin low-resistance metallic grids onto transparent contacts is a crucial development aspect for large-area OLED design. We develop a finite-element electro-optical simulation for OLED using grid structures to optimize geometry, thickness and width of grid elements. We find an exponential relationship between luminance homogeneity and grid material volume, which leads to limitations of minimal grid line width and maximal emissive area for efficient development of large-area OLED.
The influence of the main growth parameters on the growth mechanism and film formation processes during metalorganic vapor-phase epitaxy (MOVPE) of two-dimensional MoS
2
on sapphire (0001) have been ...investigated. Deposition was performed using molybdenum hexacarbonyl and di-
tert
-butyl sulfide as metalorganic precursors in a horizontal hot-wall MOVPE reactor from AIXTRON. The structural properties of the MoS
2
films were analyzed by atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. It was found that a substrate prebake step prior to growth reduced the nucleation density of the polycrystalline film. Simultaneously, the size of the MoS
2
domains increased and the formation of parasitic carbonaceous film was suppressed. Additionally, the influence of growth parameters such as reactor pressure and surface temperature is discussed. An upper limit for these parameters was found, beyond which strong parasitic deposition or incorporation of carbon into MoS
2
took place. This carbon contamination became significant at reactor pressure above 100 hPa and temperature above 900°C.
We have performed a detailed investigation of the photoluminescence features taken at 2
K on a series of Ga
x
In
1−
x
N alloys grown by metal-organic vapour-phase epitaxy through the whole ...composition range. The evolution of the photoluminescence lineshape of GaInN alloys in the indium-rich region is dominated by doping effects rather than by band-gap tailing effects correlated to existence of random chemical crystal inhomogeneities. The lineshape of the photoluminescence indicates a residual electron concentration of about 10
18–10
19
cm
−3 in the bulk part of the epilayers. The value we get for the bowing parameter is
b=2.8
eV.
Our study shows the impact of the process parameters: predose before AlN buffer deposition, SiNx deposition time, GaN growth temperature and silane injection time on growth and morphology of GaN ...nanowires (NWs) formed by a self‐organized mechanism on a silicon substrate. We determined a process parameter window for successful GaN NW growth and show how the variation of studied parameters changes the NW morphology and density. The optimization of these process parameters led to high‐density straight GaN NWs, aligned perpendicular to the substrate. The use of a preflow before AlN buffer deposition was found to be important for the successful NW formation, and most interestingly, led to a difference in structural morphology for ammonia and TMAl predose.
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