RESUMO
The spontaneous phase separation of two or more polymers is a thermodynamic process that can take place in both biological and synthetic materials and which results in the structuring of the matter from the micro- to the nanoscale. For photonic applications, it allows forming quasi-periodic or disordered assemblies of light scatterers at high throughput and low cost. The wet process methods currently used to fabricate phase-separated nanostructures (PSNs) limit the design possibilities, which in turn hinders the deployment of PSNs in commercialized products. To tackle this shortcoming, we introduce a versatile and industrially scalable deposition method based on the inkjet printing of a polymer blend, leading to PSNs with a feature size that is tuned from a few micrometers down to sub-100 nm. Consequently, PSNs can be rapidly processed into the desired macroscopic design. We demonstrate that these printed PSNs can improve light management in manifold photonic applications, exemplified here by exploiting them as a light extraction layer and a metasurface for light-emitting devices and point-of-care biosensors, respectively.
RESUMO
Future lightweight, flexible, and wearable electronics will employ visible-light-communication schemes to interact within indoor environments. Organic photodiodes are particularly well suited for such technologies as they enable chemically tailored optoelectronic performance and fabrication by printing techniques on thin and flexible substrates. However, previous methods have failed to address versatile functionality regarding wavelength selectivity without increasing fabrication complexity. This work introduces a general solution for printing wavelength-selective bulk-heterojunction photodetectors through engineering of the ink formulation. Nonfullerene acceptors are incorporated in a transparent polymer donor matrix to narrow and tune the response in the visible range without optical filters or light-management techniques. This approach effectively decouples the optical response from the viscoelastic ink properties, simplifying process development. A thorough morphological and spectroscopic investigation finds excellent charge-carrier dynamics enabling state-of-the-art responsivities >102 mA W-1 and cutoff frequencies >1.5 MHz. Finally, the color selectivity and high performance are demonstrated in a filterless visible-light-communication system capable of demultiplexing intermixed optical signals.
RESUMO
Organic chromophores that exhibit aggregation-induced emission (AIE) are of interest for applications in displays, lighting, and sensing, because they can maintain efficient emission at high molecular concentrations in the solid state. Such advantages over conventional chromophores could allow thinner conversion layers of AIE chromophores to be realized, with benefits in terms of the efficiency of the optical outcoupling, thermal management, and response times. However, it is difficult to create large-area optical quality thin films of efficiently performing AIE chromophores. Here, we demonstrate that this can be achieved by using a surface-anchored metal-organic framework (SURMOF) thin film coating as a host substrate, into which the tetraphenylethylene (TPE)-based AIE chromophore can be printed. We demonstrate that the SURMOF constrains the AIE-chromophore molecular conformation, affording efficient performance even at low loading densities in the SURMOF. As the loading density of the AIE chromophore in the SURMOF is increased, its absorption and emission spectra are tuned due to increased interaction between AIE molecules, but the high photoluminescent quantum yield (PLQY = 50% for this AIE chromophore) is maintained. Lastly, we demonstrate that patterns of the AIE chromophore with 70 µm feature sizes can be easily created by inkjet printing onto the SURMOF substrate. These results foreshadow novel possibilities for the creation of patterned phosphor thin films utilizing AIE chromophores for display or lighting applications.
RESUMO
Digital printing enables solution processing of functional materials and opens a new route to fabricate low-cost electronic devices. One crucial parameter that affects the wettability of inks for all printing techniques is the surface free energy (SFE) of the substrate. Siloxanes, with their huge variety of side chains and their ability to form self-assembled monolayers, offer exhaustive control of the substrate SFE from hydrophilic to hydrophobic. Thus, siloxane treatment is a suitable approach to adjust the substrate conditions to the desired ink, instead of optimizing the ink to an arbitrary substrate. In this work, the influence of different fluorinated and nonfluorinated siloxanes on the SFE of different substrates, such as polymers, glasses, and metals, are examined. By mixing several siloxanes, we demonstrate the fine tuning of the surface energy. The polar and dispersive components of the SFE are determined by the Owens-Wendt-Rabel-Kaelble (OWRK) method. Furthermore, the impact of the siloxanes and therefore the SFE on the pinning of droplets and wet films are assessed via dynamic contact angle measurements. SFE-optimized substrates enable tailoring the resolution of inkjet printed silver structures. A nanoparticulate silver ink was used for printing single drops, lines, and source-drain electrodes for transistors. These were examined in terms of diameter, edge quality, and functionality. We show that by adjusting the SFE of an arbitrary substrate, the printed resolution is substantially increased by minimizing the printed drop size by up to 70%.
