Additional file 1 of Large Area Nano-transfer Printing of Sub-50-nm Metal Nanostructures Using Low-cost Semi-flexible Hybrid Templates

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Transfer Printed P3HT/PCBM Photoactive Layers: From Material Intermixing to Device Characteristics

The fabrication of organic electronic devices involving complex stacks of solution-processable functional materials has proven challenging. Significant material intermixing often occurs as a result of cross-solubility and postdeposition treatments, rendering the realization of even the simplest bilayer architectures rather cumbersome. In this study we investigate the feasibility of a dry transfer printing process for producing abrupt bilayer organic photodiodes (OPDs) and the effect of thermal annealing on the integrity of the bilayer. The process involves the transfer of readily deposited thin films of poly­(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) using a polydimethylsiloxane (PDMS) stamp. Fabricated structures are characterized by means of cross-sectional scanning electron microscopy (SEM), UV/vis absorption spectroscopy, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Joint consideration of all results unveils abrupt interfaces with no thermal treatment applied and significant material intermixing for samples annealed above 100 °C. The role of the thermally assisted intermixing in determining the performance of complete devices is evaluated through the comparison of <i>J</i>–<i>V</i> characteristics and external quantum efficiencies (EQEs) of identical photodiodes subject to different annealing conditions. It is shown that the performance of such devices approaches the one of bulk heterojunction photodiodes upon thermal annealing at 140 °C for 5 min. Our results demonstrate that transfer printing is a reliable and simple process for the realization of functional multilayers, paving the way for organic electronic devices incorporating complex stacks. It further contributes to a fundamental understanding of material composition within photoactive layers by elucidating the process of thermally assisted intermixing

Fully-Sprayed and Flexible Organic Photodiodes with Transparent Carbon Nanotube Electrodes

In this study, we demonstrate the feasibility of TCO-free, fully sprayed organic photodiodes on flexible polyethylene terephthalate (PET) substrates. Transparent conducting films of single-wall carbon nanotubes are spray deposited from aqueous solutions. Low roughness is achieved, and films with sheet resistance values of 160 Ω/sq at 84% in transmittance are fabricated. Process issues related to the wetting of CNTs are then examined and solved, enabling successive spray depositions of a poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) layer and a blend of regioregular poly­(3-hexylthiophene-2,5-diyl) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). The active layer is then optimized, achieving a process yield above 90% and dark currents as low as 10^–4 mA/cm². An external quantum efficiency of 65% and high reproducibility in the performance of the devices are obtained. Finally, the impact of the characteristics of the transparent electrode (transmittance and sheet resistance) on the performances of the device are investigated and validated through a theoretical model and experimental data

Low-Cost Thermo-Optic Imaging Sensors: A Detection Principle Based on Tunable One-Dimensional Photonic Crystals

Infrared (IR) sensors employing optical readout represent a promising class of devices for the development of thermographic imagers. We demonstrate an infrared radiation detection principle based on thermally tunable one-dimensional (1D) photonic crystals acting as optical filters, integrated with organic and inorganic light emitting diodes (OLEDs and LEDs, respectively). The optical filters are composed of periodically assembled mesoporous TiO₂ and SiO₂ layers. Due to the thermal tunability of the transmission spectrum of the optical filter, the intensity of light passing through the filter is modulated by temperature. The tuned spectrum lies in the visible region and, therefore, can be directly detected by a visible-light photodetector. The thermal response of the luminance of the OLED-photonic crystal ensemble is 3.8 cd m^–2 K^–1. Furthermore, we demonstrate that the local temperature profile can be time and spatially resolved with a resolution of 530 by 530 pixel, thus enabling a potential application as an infrared imaging sensor featuring low power consumption and low fabrication costs

Humidity-Enhanced Thermally Tunable TiO₂/SiO₂ Bragg Stacks

Tunable, stimuli-responsive photonic crystals (PCs) have developed into a fast growing, interdisciplinary research field attracting attention from various scientific communities, such as photonics, sensing, and materials chemistry. Here, we propose a thermally tunable and environmentally responsive optical filter derived from nanoparticle-based TiO₂/SiO₂ one-dimensional photonic crystals, christened Bragg stacks (BSs). Photonic crystals with textural mesoporosity were obtained by bottom-up assembly based on sequential spin-coating suspensions of TiO₂ and SiO₂ nanoparticles on glass substrates. The mechanism of the BS thermal tunability is based on the thermo-optic effect, i.e., dependence of the refractive index on temperature. Notably, the optical response of the BS to temperature can be significantly enhanced by varying the relative humidity of the environment. Thus, the magnitude of the spectral shift increases more than fourfold from 4.4 to 21.9 nm with a change in relative humidity from 25% to 55% in the temperature range between 15 and 60 °C. Thus, humidity-enhanced thermal tuning causes shifts of the transmission spectra by up to −1.66 nm K^–1. The simulations of the wavelength shift based on the measurement of the effective thermo-optic coefficient of the individual TiO₂ and SiO₂ layers at ambient conditions closely correspond to the experimental values. Owing to their high inherent porosities and ease of fabrication, nanoparticle-based BSs offer a great potential for the development of sensitive, label-free photonic crystal temperature and humidity sensors

Conductance Enhancement of InAs/InP Heterostructure Nanowires by Surface Functionalization with Oligo(phenylene vinylene)s

We have investigated the electronic transport through 3 μm long, 45 nm diameter InAs nanowires comprising a 5 nm long InP segment as electronic barrier. After assembly of 12 nm long oligo(phenylene vinylene) derivative molecules onto these InAs/InP nanowires, we observed a pronounced, nonlinear <i>I</i>–<i>V</i> characteristic with significantly increased currents of up to 1 μA at 1 V bias, for a back-gate voltage of 3 V. As supported by our model calculations based on a nonequilibrium Green Function approach, we attribute this effect to charge transport through those surface-bound molecules, which electrically bridge both InAs regions across the embedded InP barrier