H-aggregate analysis of P3HT thin films-Capability and limitation of photoluminescence and UV/Vis spectroscopy.

Polymer morphology and aggregation play an essential role for efficient charge carrier transport and charge separation in polymer-based electronic devices. It is a common method to apply the H-aggregate model to UV/Vis or photoluminescence spectra in order to analyze polymer aggregation. In this work we present strategies to obtain reliable and conclusive information on polymer aggregation and morphology based on the application of an H-aggregate analysis on UV/Vis and photoluminescence spectra. We demonstrate, with P3HT as model system, that thickness dependent reflection behavior can lead to misinterpretation of UV/Vis spectra within the H-aggregate model. Values for the exciton bandwidth can deviate by a factor of two for polymer thicknesses below 150 nm. In contrast, photoluminescence spectra are found to be a reliable basis for characterization of polymer aggregation due to their weaker dependence on the wavelength dependent refractive index of the polymer. We demonstrate this by studying the influence of surface characteristics on polymer aggregation for spin-coated thin-films that are commonly used in organic and hybrid solar cells.

Metal-organic framework@microporous organic network: hydrophobic adsorbents with a crystalline inner porosity.

This work reports the synthesis and application of metal-organic framework (MOF)@microporous organic network (MON) hybrid materials. Coating a MOF, UiO-66-NH2, with MONs forms hybrid microporous materials with hydrophobic surfaces. The original UiO-66-NH2 shows good wettability in water. In comparison, the MOF@MON hybrid materials float on water and show excellent performance for adsorption of a model organic compound, toluene, in water. Chemical etching of the MOF results in the formation of hollow MON materials.

Role of additional PCBM layer between ZnO and photoactive layers in inverted bulk-heterojunction solar cells.

In order to induce greater light absorption, nano-patterning is often applied to the metal-oxide buffer layer in inverted bulk-heterojunction(BHJ) solar cells. However, current homogeneity was significantly disturbed at the interface, leading to an efficiency that was not fully optimized. In this work, an additional PC61BM layer was inserted between the ZnO ripple and the photoactive layer to enhance the electron extraction. The insertion of additional PC61BM layer provided substantial advantages in the operation of inverted BHJ solar cells; specifically, it enhanced current homogeneity and lowered accumulation and trapping of photogenerated charges at the ZnO interface. Inclusion of the additional PC61BM layer led to effective quenching of electron-hole recombination by a reduction in the number of accumulated charges at the surface of ZnO ripples. This resulted in a 16% increase in the efficiency of inverted BHJ solar cells to 7.7%, compared to solar cells without the additional PC61BM layer.

Surface modification of a ZnO electron-collecting layer using atomic layer deposition to fabricate high-performing inverted organic photovoltaics.

A ripple-structured ZnO film as the electron-collecting layer (ECL) of an inverted organic photovoltaic (OPV) was modified by atomic layer deposition (ALD) to add a ZnO thin layer. Depositing a thin ZnO layer by ALD on wet-chemically prepared ZnO significantly increased the short-circuit current (Jsc) of the OPV. The highest power conversion efficiency (PCE) of 7.96% with Jsc of 17.9 mA/cm2 was observed in the inverted OPV with a 2-nm-thick ALD-ZnO layer, which quenched electron-hole recombination at surface defects of ZnO ripples. Moreover, an ALD-ZnO layer thinner than 2 nm made the distribution of electrical conductivity on the ZnO surface more uniform, enhancing OPV performance. In contrast, a thicker ALD-ZnO layer (5 nm) made the two-dimensional distribution of electrical conductivity on the ZnO surface more heterogeneous, reducing the PCE. In addition, depositing an ALD-ZnO thin layer enhanced OPV stability and initial performance. We suggest that the ALD-ZnO layer thickness should be precisely controlled to fabricate high-performing OPVs.

A high-performing nanostructured TiO2 filter for volatile organic compounds using atomic layer deposition.

Novel nanostructured gas filtering systems with TiO(2) thin films using atomic layer deposition (ALD) were developed for volatile organic compounds. A superior toluene adsorption efficiency was found for the nanostructured TiO(2) thin films.

CO oxidation of Pt nanostructures supported by TiO2/Ti.

This study examined the CO oxidation reactivity of Pt deposited on TiO2. The Pt catalysts were prepared by the evaporation of Pt on Ti foils covered with TiO2, and their surface structures were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Separate Pt nanoparticles could be observed with lower amounts of deposited Pt (<2 nm). With increasing Pt thickness, these Pt nanoparticles appeared to agglomerate into more complicated nanostructures. When approximately 5 nm of Pt was deposited, the TiO2 surface was almost completely covered by Pt. Additional deposition of Pt on these complete Pt-layers resulted in the deposition of small nanoparticles (approximately 5 nm) on top of the Pt underlayer. The CO oxidation reactivity at 160 degrees C, normalized with respect to the Pt thickness, initially decreased with increasing amount of Pt. This was attributed mainly to the decrease in the surface-to-volume ratio. However, the reactivity increased when the amount of Pt exceeded 5 nm, which can be rationalized in part by the unique structural properties of Pt-films according to SEM imaging. We also suggest that a stronger influence of the metal-support interactions at lower Pt coverages results in reduced catalytic activity.