In this work, the thermoelectric (TE) properties of poly(3,4- ethylenedioxylthiophene):poly(styrene sulfonate) (PEDOT:PSS) thin films at room temperature are studied. Different methods have been applied for tuning the TE properties: 1st addition of polar solvent, dimethyl sulfoxide (DMSO), into the PEDOT:PSS solution; 2nd post-treatment of thin films with a mixture of DMSO and ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4). It is verified that DMSO post-treatment is more efficient than DMSO addition in improving the electrical conductivity with a trivial change in the Seebeck coefficient. The power factor is increased up to 30.1 W mK-2 for the film with DMSO post-treatment, while the optimized power factor by DMSO addition is 18.2 W mK-2. It is shown that both DMSO addition and post-treatment induce morphological changes: an interconnected network of elongated PEDOT grains is generated, leading to higher electrical conductivity. In contrast, for t hose films post-treated in the presence of EMIMBF4, an interconnected network of short and circular PEDOT grains with increased polaron density is created, resulting in the improvement in the Seebeck coefficient and a concomitant compromise in the electrical conductivity. An optimized power factor of 38.46 W mK -2 is achieved at 50 vol% of EMIMBF4, which is the highest reported so far for PEDOT:PSS thin films to our knowledge. Assuming a thermal conductivity of 0.17 W mK-1, the corresponding ZT is 0.068 at 300 K. These results demonstrate that post-treatment is a promising approach to enhance the TE properties of PEDOT:PSS thin films. Furthermore, ionic liquid, EMIMBF4, shows the potential for tuning the TE properties of PEDOT:PSS thin films via a more environmentally benign process
We report about a detailed comparison of the additive manufacturing methods inkjet printing (IJP) and aerosol jet printing (AJP). Both technologies are based on the direct-writing approach enabling the non-contact deposition of various materials in flexible patterns, e.g., for printed electronic applications. The deposited pattern elements were classified as (i) drops (IJP) or splats (AJP), (ii) lines, and (iii) squares. These elements can be considered as basic elements of the deposition systems and also of printed electronics. The pattern elements were deposited with IJP and AJP using the same silver nanoparticle ink. After printing, the layers were characterized regarding their morphology by optical and topographical measurement methods as well as regarding their electrical characteristics. It turned out that drops deposited with IJP and splats deposited with AJP can have similar dimensions. However, the shapes of the deposits differ widely. In the case of lines, AJP enables narrower line widths and thinner line thicknesses in comparison to IJP. In IJP, the line morphology varies depending on the direction of the deposition. Finally, the morphology of the deposited lines determines the electrical conductivity. For printed squares, the IJP layers show much higher layer thickness and a different layer topography compared with AJP as result of a higher volume per area deposition of materials
The functionality of common organic semiconductor materials is determined by their chemical structure and crystal modification. While the former can be fine-tuned via synthesis, a priori control over the crystal structure has remained elusive. We show that the surface tension is the main driver for the plate-like crystallization of a novel small organic molecule n-type semiconductor at the liquid-air interface. This interface provides an ideal environment for the growth of millimeter-sized semiconductor platelets that are only few nanometers thick and thus highly attractive for application in transistors. On the basis of the novel high-performance perylene diimide, we show in as-grown, only 3 nm thin crystals electron mobilities of above 4 cm/(V s) and excellent bias stress stability. We suggest that the established systematics on solvent parameters can provide the basis of a general framework for a more deterministic crystallization of other small molecules.
The thermal atomic layer deposition (ALD) of copper oxide films from the nonfluorinated yet liquid precursor bis(tri- n -butylphosphane)copper(I)acetylacetonate, [(Bnu3normalP)C2normalu(acac)] , and wet O2 on Ta, TaN, Ru, and SinormalO2 substrates at temperatures of <160°C is reported. Typical temperature-independent growth was observed at least up to 125°C with a growth-per-cycle of ∼0.1Å for the metallic substrates and an ALD window extending down to 100°C for Ru. On SinormalO2 and TaN, the ALD window was observed between 110 and 125°C , with saturated growth shown on TaN still at 135°C . Precursor self-decomposition in a chemical vapor deposition mode led to bimodal growth on Ta, resulting in the parallel formation of continuous films and isolated clusters. This effect was not observed on TaN up to ∼130°C and neither on Ru or SinormalO2 for any processing temperature. The degree of nitridation of the tantalum nitride underlayers considerably influenced the film growth. With excellent adhesion of the ALD films on all substrates studied, the results are a promising basis for Cu seed layer ALD applicable to electrochemical Cu metallization in interconnects of ultralarge-scale integrated circuits.
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