2D hybrid organic–inorganic perovskites are valued in optoelectronic applications for their tunable bandgap and excellent moisture and irradiation stability. These properties stem from both the ...chemical composition and crystallinity of the layer formed. Defects in the lattice, impurities, and crystal grain boundaries generally introduce trap states and surface energy pinning, limiting the ultimate performance of the perovskite; hence, an in‐depth understanding of the crystallization process is indispensable. Here, a kinetic and thermodynamic study of 2D perovskite layer crystallization on transparent conductive substrates are provided—fluorine‐doped tin oxide and graphene. Due to markedly different surface structure and chemistry, the two substrates interact differently with the perovskite layer. A time‐resolved grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) is used to monitor the crystallization on the two substrates. Molecular dynamics simulations are employed to explain the experimental data and to rationalize the perovskite layer formation. The findings assist substrate selection based on the required film morphology, revealing the structural dynamics during the crystallization process, thus helping to tackle the technological challenges of structure formation of 2D perovskites for optoelectronic devices.
Conductive substrates are essential components of optoelectronic devices based on 2D hybrid organic–inorganic perovskites. They provide electrical contact but also influence the crystallinity of the perovskite layer. The influence of two representative conductive substrates, FTO and graphene, on the crystallization of the epitaxial perovskite layer is investigated by GIWAXS and computational methods to rationalize the substrate choice for a particular device.
Herein we explore the possibility to control the fabrication of non‐equilibrium nano‐patterns of spin‐coated organic‐inorganic hybrid materials based on diblock copolymers and metal nanoparticles in ...thin films. It is demonstrated that the type of solvent and the initial solution concentration, among other factors, can serve as tools to direct the morphology of spin‐coated thin films. The driving forces leading to the pattern formation are reviewed with respect to these parameters—type of solvents and polymer concentration. As a result well‐defined surface patterns of functional hybrid materials are obtained. Moreover, the same tools used to direct the pattern formation can be applied to gain control over the particle size and size distribution.
Nanostructured thin films are generated via self‐assembly of functional hybrid materials based on a diblock copolymer and inorganic nanoparticles. The pattern formation can be controlled by a narrow selection of tools. Here we demonstrate the effect of the solvent type and the polymer concentration as tools to control the morphology in thin films of these hybrid materials. Simultaneously, the characteristic length scale of the nano‐pattern as well as the particle size are adjusted.
A high‐performance W/B4C multilayer mirror with 80 periods of nominally 1.37 nm was measured by grazing‐incidence small‐angle X ray scattering (GISAXS) in order to analyse the lateral and vertical ...correlations of the interface roughness within the framework of a scaling concept of multilayer growth. A dynamic growth exponent z = 2.19 (7) was derived, which is close to the value predicted by the Edwards–Wilkinson growth model. The effective number of correlated periods indicates a partial replication of the low interface roughness frequencies. A simulation of the GISAXS pattern based on the Born approximation suggests a zero Hurst fractal parameter H and a logarithmic type of autocorrelation function. The as‐deposited mirror layers are amorphous and exhibit excellent thermal stability up to 1248 K in a 120 s rapid thermal vacuum annealing process. At higher temperatures, the B4C layers decompose and poorly developed crystallites of a boron‐rich W–B hexagonal phase are formed, and yet multilayer collapse is not complete even at 1273 K. Ozone treatment for 3000 s in a reactor with an ozone concentration of 150 mg m−3 results in the formation of an oxidized near‐surface region of a thickness approaching ∼10% of the total multilayer thickness, with a tendency to saturation.
A high-performance W/B
4
C multilayer mirror with 80 periods of nominally 1.37 nm was measured by grazing-incidence small-angle X ray scattering (GISAXS) in order to analyse the lateral and vertical ...correlations of the interface roughness within the framework of a scaling concept of multilayer growth. A dynamic growth exponent
z
= 2.19 (7) was derived, which is close to the value predicted by the Edwards–Wilkinson growth model. The effective number of correlated periods indicates a partial replication of the low interface roughness frequencies. A simulation of the GISAXS pattern based on the Born approximation suggests a zero Hurst fractal parameter
H
and a logarithmic type of autocorrelation function. The as-deposited mirror layers are amorphous and exhibit excellent thermal stability up to 1248 K in a 120 s rapid thermal vacuum annealing process. At higher temperatures, the B
4
C layers decompose and poorly developed crystallites of a boron-rich W–B hexagonal phase are formed, and yet multilayer collapse is not complete even at 1273 K. Ozone treatment for 3000 s in a reactor with an ozone concentration of 150 mg m
−3
results in the formation of an oxidized near-surface region of a thickness approaching ∼10% of the total multilayer thickness, with a tendency to saturation.
Cosolvent addition of glycerol (G) and the use of the cosolvent ethylene glycol (EG) increase the conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) films to values ...on the order of indium tin oxide conductivity. The underlying morphological changes are probed via scanning electron microscopy as well as advanced scattering techniques microfocused grazing incidence small- and wide-angle X-ray scattering. The enhancement in conductivity is ascribed to fundamental morphological changes and molecular reorientation within crystalline domains. Thereby, the conductivity enhancement is directly correlated to domain ruptures toward smaller and more densely packed PEDOT domains together with an enhanced crystallinity, the removal of PSS molecules, and moreover a reorientation of the conjugated PEDOT molecules. The latter is reported and quantified here for PEDOT:PSS films for the first time.
Printing of active layers of high-efficiency organic solar cells and morphology control by processing with varying solvent additive concentrations are important to realize real-world use of ...bulk-heterojunction photovoltaics as it enables both up-scaling and optimization of the device performance. In this work, active layers of the conjugated polymer with benzodithiophene units PBDB-T-SF and the nonfullerene small molecule acceptor IT-4F are printed using meniscus guided slot-die coating. 1,8-Diiodooctane (DIO) is added to optimize the power conversion efficiency (PCE). The effect on the inner nanostructure and surface morphology of the material is studied for different solvent additive concentrations with grazing incidence small-angle X-ray scattering (GISAXS), grazing incidence wide-angle X-ray scattering (GIWAXS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Optical properties are studied with photoluminescence (PL), UV/vis absorption spectroscopy, and external quantum efficiency (EQE) measurements and correlated to the corresponding PCEs. The addition of 0.25 vol % DIO enhances the average PCE from 3.5 to 7.9%, whereas at higher concentrations the positive effect is less pronounced. A solar cell performance of 8.95% is obtained for the best printed device processed with an optimum solvent additive concentration. Thus, with the large-scale preparation method printing similarly well working solar cells can be realized as with the spin-coating method.
Optically responsive materials are present in everyday life, from screens to sensors. However, fabricating large-area, fossil-free materials for functional biocompatible applications is still a ...challenge today. Nanocelluloses from various sources, such as wood, can provide biocompatibility and are emerging candidates for templating organic optoelectronics. Silver (Ag) in its nanoscale form shows excellent optical properties. Herein, we combine both materials using thin-film large-area spray-coating to study the fabrication of optical response applications. We characterize the Ag nanoparticle formation by X-ray scattering and UV–vis spectroscopy in situ during growth on the nanocellulose template. The morphology and optical properties of the nanocellulose film are compared to the rigid reference surface SiO2. Our results clearly show the potential to tailor the energy band gap of the resulting hybrid material.
Many nanoscale biopolymer building blocks with defect-free molecular structure and exceptional mechanical properties have the potential to surpass the performance of existing fossil-based materials ...with respect to barrier properties, load-bearing substrates for advanced functionalities, as well as light-weight construction. Comprehension and control of performance variations of macroscopic biopolymer materials caused by humidity-driven structural changes at the nanoscale are imperative and challenging. A long-lasting challenge is the interaction with water molecules causing reversible changes in the intrinsic molecular structures that adversely affects the macroscale performance. Using in situ advanced X-ray and neutron scattering techniques, we reveal the structural rearrangements at the nanoscale in ultrathin nanocellulose films with humidity variations. These reversible rearrangements are then correlated with wettability that can be tuned. The results and methodology have general implications not only on the performance of cellulose-based materials but also for hierarchical materials fabricated with other organic and inorganic moisture-sensitive building blocks.
The reproducible low-cost fabrication of functional polymer–metal interfaces via self-assembly is of crucial importance in organic electronics and organic photovoltaics. In particular, submonolayer ...and nanogranular systems expose highly interesting electrical, plasmonic, and catalytic properties. The exploitation of their great potential requires tailoring of the structure on the nanometer scale and below. To obtain full control over the complex nanostructural evolution at the polymer–metal interface, we monitor the evolution of the metallic layer morphology with in situ time-resolved grazing-incidence small-angle X-ray scattering during sputter deposition. We identify the impact of different deposition rates on the growth regimes: the deposition rate affects primarily the nucleation process and the adsorption-mediated growth, whereas rather small effects on diffusion-mediated growth processes are observed. Only at higher rates are initial particle densities higher due to an increasing influence of random nucleation, and an earlier onset of thin film percolation occurs. The obtained results are discussed to identify optimized morphological parameters of the gold cluster ensemble relevant for various applications as a function of the effective layer thickness and deposition rate. Our study opens up new opportunities to improve the fabrication of tailored metal–polymer nanostructures for plasmonic-enhanced applications such as organic photovoltaics and sensors.
Solution‐processed organic bulk heterojunction solar cells based on poly(3‐hexylthiophene) (P3HT) blended with 6,6‐phenyl‐C60‐butyric acid methyl ester are doped with different concentrations of iron ...(II,III) oxide nanoparticles (Fe3O4). The power conversion efficiency of the devices doped at low concentrations is improved up to 11%. The improvement finds its origin in a lower recombination current, which is a consequence of an increased effective exciton lifetime according to the J–V characteristics and the optoelectronical analysis of the films. The increase in performance cannot be attributed to changes in morphology or crystallinity according to grazing‐incidence X‐ray scattering experiments. The evolution of the solar cell short‐circuit current at low doping concentrations is related to variations in the arrangement of the crystalline regions of P3HT. For high doping concentrations (above 1.0 wt%) the performance of the solar cell decays rapidly, ascribed to the increased leakage currents in the device caused by the presence of nanoparticles.
Organic solar cells are doped with iron oxide nanoparticles. An increased efficiency for low doping concentrations is found and ascribed to a reduced device recombination, which is traced with prompt and delayed fluorescence measurements. Morphological and crystalline characterization is addressed by grazing‐incidence small/wide‐angle X‐ray scattering in order to ensure that the improvement is not morphology related.
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