Deposition/printing of materials with sub-1 μm precision and size (cross sections) is required for optical and electrical micro-devices. Crystalline c-ITO (Indium tin oxide) nanostructures were patterned on glass with a precision that formed gaps of 20-50 nm between individual disks or lines of ∼ 250 nm diameter or width. The absorbed energy density [J/cm3] followed the second order dependence on pulse energy. This facilitated high resolution and precision for nanoscale laser writing at the 515 nm laser wavelength. Patterns for optical elements such as circular gratings and micro-disks were laser printed using ITO as a resist. Unexposed amorphous a-ITO was chemically removed in aqueous 1% vol. HF solution. This use of a-ITO as solid-resist is promising for metamaterial and micro-optical applications.

Adhesion of polymers to surfaces is of upmost importance in timely applications such as protective coatings, biomaterials, sensors, new power sources and soft electronics. In this context, this work examines the role of molecular interactions in the adhesion of polypyrrole thin films to flexible Indium Tin Oxide (ITO) electrodes grafted with aryl layers from various diazonium salts, namely 4-carboxybenzenediazonium (ITO-CO₂H), 4-sulfonicbenzenediazonium (ITO-SO₃H), 4-N,N dimethylbenzenediazonium (ITO-N(CH₃)₂), 4-aminobenzenediazonium (ITO-NH₂), 4-cyanobenzenediazonium (ITO-CN) and 4-N-phenylbenzenediazonium (ITO-NHPh). It was demonstrated that PPy thin layers were adherent to these surfaces, whereas adhesion failure was noted on bare ITO, following simple solvent washing or sonication. Adhesion of the polypyrrole was investigated in terms of the hydrophilic/hydrophobic character of the underlying aryl layer as probed by contact angle measurements. It was found that sulfonic acid doped polypyrrole (PPy-BSA) thin films were preferably deposited on the most hydrophobic surfaces. More importantly, the redox properties and electrochemical impedance of PPy were closely related to the hydrophobic character of the aryl layers. This work demonstrates that diazonium compounds are unique molecular glues for conductive polymers, and permit to tune their interfacial properties. With diazonium-based robust, architectured interfaces, one can design high performance materials for e.g.sensors, printed soft electronics and flexible thermoelectrics.

Here we report highly efficient, indium tin oxide (ITO)-free polymer solar cells (PSCs) with an ultrathin copper (Cu) film(~10 nm) coated with a thin layer of poly[(9,9-bis(3‘-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) as transparent electrode. Despite of its lower far-field transmittance of the electrode, the obtained ITO-free device based on the ultrathin Cu film can delivery higher absorption efficiency than that of the device based on ITO substrate in the long wavelength region, which can be attributed to the formation of metal resonant microcavity between the opaque back metal mirror (MoO3/Al electrode) and the transparent Cu film with high reflectance. As a result, polymer solar cells based on poly[[2,6'-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene][3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7-Th) and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) blend show a high power conversion efficiency (PCE) of 8.21 %, comparable to that of the control device based on ITO electrode (with a PCE of 9.60% ). The results demonstrate that thermally evaporated Cu thin film electrode can be promising candidate to replace ITO for highly efficient PSCs, thus may open up the possibility for massive production of PSCs with low cost.

Recently, Indium Tin Oxide, a highly transparent, well conductive, and CMOS-compatible material, has been paying strong attention to the thermo-optic controlled silicon photonics industry because it allows a miniature of the gap between the core silicon and the heater, thus enabling reducing the electric power consumption and enhancing the switching speed. In this article, we propose an ultralow loss and small-size ITO microheater for the phase shift tuning. The designated microheater is manipulated in realizing a numerical co-design of compact and high bandwidth three-mode converter and three-mode selective router. Simulation results illustrate the 3-dB bandwidth for the three-mode converter and three-mode selective router as much as 100-nm and 40-nm during crosstalk under -25 dB, respectively. Besides, co-designed devices attain relatively large fabrication tolerances corresponding to width and height tolerances of ±50 nm and ±5 nm. In addition, the proposed devices consumed less than 90 mW total power consumption and took a fast switching time below 8 μs. Moreover, both two co-designs can be integrated into an estimated compact footprint of 8 μm2160 μm. Such excellent performances demonstrate the attractive potential of ITO as low-loss thermo-optic phase shifters and open an alternative way for enabling ultrafast and high-speed mode division multiplexing systems and very large-scale photonic integrated circuits.

Low-temperature processed ITO thin films offer the potential of overcoming the doping limit by suppressing the equilibrium of compensating oxygen interstitial defects. To elucidate this potential, electrical properties of Sn-doped In₂O₃ (ITO) thin films are studied in dependence on film thickness. In-operando conductivity and Hall effect measurements during annealing of room temperature deposited films with different film thickness in different environments allow to discriminate between the effects of crystallization, grain growth, donor activation and oxygen diffusion on carrier concentrations and mobilities. At 200 °C, a control of carrier concentration by oxygen incorporation or extraction is only possible for very thin films. The electrical properties of thicker films deposited at room temperature are mostly affected by grain size. The remaining diffusivity of compensating oxygen defects at 200 °C is sufficient to screen the high Fermi level induced by deposition of Al₂O₃ using atomic layer deposition (ALD), which disables the use of defect modulation doping at this temperature. The results indicate that achieving higher carrier concentrations requires a control of the oxygen pressure during deposition in combination with seed layers to enhance crystallinity or the use of near room temperature ALD.