Organic Thin Film Research Articles

High mobility wide bandgap polymer realized by a combined modification strategy of processing solvent and dielectric interface

High mobility organic thin film transistors (OTFTs) are realized through a combined modification strategy of processing solvent and dielectric interface when a wide bandgap donor-acceptor conjugated polymer PBODT with edge-on orientation and high crystallinity was applied. The pre-aggregation ability of PBODT in different solvents exhibits different crystallinity but remains typical edge-on orientation. Moreover, the surface energy modulation of the semiconductor/dielectric interface enhances the transport property of PBODT, delivering a high mobility of 3.68 cm2V−1s−1. In addition, a comparable mobility of 3.06 cm2V−1s−1 is demonstrated via the eco-friendly solvent mesitylene. The results have demonstrated that the synergy of solvent and dielectric interface can provide new vitality for the application of high-performance environmentally friendly OTFTs.

Structural and Magnetic Properties of a Drop-Cast C54H34Br4CuO4 β-Diketonato Complex Film on a Graphite Surface.

The structural and magnetic properties of a drop-cast film of flat C54H34Br4CuO4, a β-diketonato complex functionalized with bromine atoms, on a graphite surface are investigated using scanning tunneling microscopy, synchrotron X-ray absorption spectroscopy, and X-ray magnetic circular dichroism. Experimental measurements reveal that the Cu-complexes preferentially lay flat on the graphite surface. The magnetic hysteresis loops show that the organic thin film remains paramagnetic at 2 K with an easy axis of magnetization perpendicular to the graphite surface and is therefore perpendicular to the plane of the Cu-complex skeleton.

Opportunities for cost-effective manufacturing of fully printed high performance displays enabled by vertical light-emitting transistor pixels

With the vertical organic light-emitting transistor (VOLET), we introduce a promising solution that could significantly benefit the manufacturing of displays, accelerating the wide adoption of flexible and printed electronics. The VOLET—like conventional, lateral channel, organic thin film transistors—is compatible with a variety of printing techniques as well as flexible substrates and low-temperature processing. In combination these devices will enable a more cost-effective approach to mass-production that can dramatically extend the market potential of active-matrix organic light-emitting diode (AMOLED) displays. In this paper we discuss the prospects that AMOLED presents for the future of the display market, with a focus on the innovative VOLET device architecture. We assess how the integration of this device into active-matrix displays can contribute to the long range sustained competitiveness of AMOLED technology. We review recent progress in mass production techniques for printed electronics, with a particular emphasis on large-scale carbon nanotube material deposition. Finally, we explore the prospects for fully printed active-matrix light-emitting displays, including a review of high-performance printed components whose integration could facilitate the mass production of low-cost, high-performance, VOLET based AMOLEDs.

Ultrathin, Flexible, and Reusable Silicon Shadow Masks Manipulated via Transfer Printing

Stencil lithography is a facile patterning technique that offers a potential solution to the limitations of conventional photolithography. However, several critical factors such as enhanced pattern resolution, ability to pattern on nonplanar surfaces, and multilayer patterning should further be addressed to extend the applications of stencil lithography. This study presents a novel ultrathin silicon shadow mask which is flexible, reusable, and able to be precisely aligned and manipulated through transfer printing. The small thickness of the silicon shadow mask inherently provides it with the enhanced resolution patterning on both planar and nonplanar surfaces. To highlight these attractive benefits, substrates are patterned with metal deposition as well as by etching in a multilayer configuration. Moreover, it is found that the pattern resolution which is degraded as the shadow mask is repeatedly coated with metal and becomes warped can be restored after the mask cleaning procedure, demonstrating its effective reusability. Finally, as a device‐level application, top contact/bottom gate organic thin film transistor arrays are fabricated on both planar and curved surfaces using the shadow mask. These results show the promise of stencil lithography as a versatile and reliable high resolution patterning method for various applications by exploiting the presented ultrathin silicon shadow mask.

(Invited) Structural and Dynamics Analysis of Organic Semiconducting Materials by Solid State NMR

Recently, our group have successfully developed several blue and green thermally activated delayed fluorescence (TADF) emitters showing high external quantum efficiencies in OLEDs through high-throughput screening based on quantum chemical calculations. Although the conformation, aggregated structure and dynamics of TADF emitters in amorphous states is expected to be the origin of reverse intersystem crossing and resulting high device performance, the experimental approach toward these information is still limited because typical diffraction technique cannot be used to amorphous materials due to the lack of long-range order. Thus we have carried out multiscale simulations and solid-state NMR (ssNMR) analysis of organic amorphous thin films. The ssNMR is one of the powerful technique to obtain the structural and dynamics information of amorphous aggregated materials. In this presentation, we demonstrate structural and dynamics analysis of amorphous organic semiconducting materials using ssNMR.Reference(1) “Analysis of Molecular Orientation in Organic Semiconducting Thin Films Using Static Dynamic Nuclear Polarization Enhanced Solid-State NMR Spectroscopy”, Suzuki, K.; Kubo, S.; Aussenac, F.; Engelke, F.; Fukushima, T.; Kaji, H. Angew. Chem. Int. Ed. 2017, 56, 14842.(2) “Efficient blue thermally activated delayed fluorescence emitters showing very fast reverse intersystem crossing”, Ren, Y., Wada, Y., Suzuki, K., Kusakabe, Y., Geldsetzer, J. and Kaji, H. Appl. Phys. Express, 2021, 14, 071003.(3) “Solution-processable thermally activated delayed fluorescence emitters for application in organic light emitting diodes”, Suzuki, K.; Adachi, C.; Kaji, H. J. Soc. Inf. Disp. 2017, 25, 480.(4) “Imidazole Acceptor for Both Vacuum-Processable and Solution-Processable Efficient Blue Thermally Activated Delayed Fluorescence”, Kusakabe, Y.; Wada, Y.; Misono, T.; Suzuki, K.; Shizu, K.; Kaji, H ACS Omega, 7, 16740 - 16745 (2022).(5) “Triarylboron-based Fluorescent Organic Light-emitting Diodes with External Quantum Efficiencies Exceeding 20%”, Suzuki, K.; Kubo, S.; Shizu, K.; Fukushima, T.; Wakamiya, A.; Murata, Y.; Adachi, C.; Kaji, H.; Angew. Chem. Int. Ed. 2015, 54, 15231.(5) “Purely organic electroluminescent material realizing 100% conversion from electricity to light”, Kaji, H.; Suzuki, H.; Fukushima, T.; Shizu, K.; Suzuki, K.; Kubo, S.; Komino, T.; Oiwa, H.; Suzuki, F.; Wakamiya, A.; Murata, Y.; Adachi, C. Nat. Commun. 2015, 6, 8476.

Phthalocyanine-Based Organic Thin Film Transistors as a Platform for Cannabinoid Sensors

With a growing international trend of Cannabis legalization, there is a present need for on-the-spot, low cost, and rapid differentiation of cannabinoids. The two primary cannabinoids, Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), obtained from Cannabis, elicit very different pharmacological effects necessitating consumer and industry methods for their detection and rapid speciation. CuPc and F16-CuPc, well characterized p- and n-type semiconductors respectively, are used as the OTFT semiconducting layer in combination with a cannabinoid-sensitive chromophore allowing for the differentiation of THC and CBD. Device analysis of pre- and post-pyrolyzed rapid plant extract samples was able to predict the THC/CBD ratio with HPLC accuracy. Spectroelectrochemistry was used to probe molecular interactions between cannabinoids with and without a cannabinoid sensitive chromophore against a variety of Pcs. Spectroelectrochemical changes to the Q-band region of the Pc spectra in the presence of analytes was related to modified ratios of Pc-Pc orientations in solution, streamlining material selection, reducing manufacturing burden, and expediting sensor development. 2D-NMR was used to further elucidate unique Pc-Pc and Pc-analyte interactions, providing additional insight on atomic level interactions. Through altered Pc-Pc orientations, analytes can induce physical alterations to Pc thin-film morphology and structure, consequently, modifying electrical performance beyond charge trapping effects. Pc peripheral and axial substitutions allow an additional level of Pc tunability and their relationship with analyte interactions, film structure, and OTFT sensing performance was explored.We established relationships between thin-films of phthalocyanines (Pcs) with a variety of central, peripheral, and axial substituents and their response to THC. X-Ray diffraction and UV–vis absorption spectroscopy measurements demonstrate significantly altered film morphologies and the formation of new crystal orientations in response to analytes, which are corroborated by scanning electron microscopy. With exposure to THC, aluminium chloride Pc generates the largest physical film changes as well as the largest changes in OTFT performance. These findings have implications for Pc-based OTFT sensor design, suggesting that the semiconducting Pc thin-film morphologies are not static in the presence of analytes, and that the sensing response is driven both by strong analyte-Pc coordination and bulk film restructuring to accommodate these interactions.References Advanced Functional Materials, 2021, ASAP, doi:10.1002/adfm.202107138ACS Appl. Mater. Interfaces, 2020, 12, 45, 50692–50702ACS Sensors, 2019, 4, 10, 2706-2715. Figure 1

Thin Film Transistors Incorporating Ultrapure Semiconducting Single-Walled Carbon Nanotubes and Green Dielectrics

Printed electronics is a burgeoning field that has received intense research interest and is beginning to experience commercial successes. Single-walled carbon nanotubes (SWNTs) are a unique and promising building block for incorporation into next generation superfast electronic devices. SWNTs have very high carrier mobilites, with band gaps compatible for integration into logic circuits. Their excellent mechanical flexibility allows for potential incorporation into flexible printed electronics, enabling fully-printed transistors and circuits with performances that support low cost, large area fabrication. Progress in incorporating SWNTs into commercial devices has been hindered by the presence of metallic SWNTs, which are produced alongside semiconducting SWNTs during synthesis, and negatively impact device performance. Fabrication of ambipolar SWNT organic thin film transistors (OTFTs) with high carrier mobilities and high on/off ratios remains particularly challenging; many examples in the literature required high temperature, expensive and energy-demanding processes.Since the initial discovery of conjugated polymer-assisted dispersion and purification of SWNTs in 2008, several polymer families have been successfully shown to selectively disperse semiconducting SWNTs. However, only a relatively small number of these supramolecular complexes have been incorporated into OTFTs. We used a novel conjugated polymer to exclusively disperse semiconducting SWNTs. The dispersal procedure requires a simple sonication and centrifugation, during which the metallic SWNTs sediment out. Solution purity was evaluated using UVVis- NIR and Raman spectroscopies. The resulting dispersions are amenable to solution processing techniques such drop casting and spin coating, allowing for the potential for large area device fabrication at room temperature. Ambipolar OTFTs were fabricated under ambient conditions using this solution and tested in both air and under inert atmosphere. The presence of excess conjugated polymer, solution deposition techniques, SWNT density, surface treatment, and post-fabrication treatment were all investigated to determine which parameters facilitated the production of OTFTs with high mobilities (>20 cm2V-1s-1), high on/off ratios (10^6-10^8), negligeble hysteresis, controlled threshold voltages, and high bias stability.[1] Protocols for sorting and dispersing ultrapure sc-SWNTs with conjugated polymers for thin-film transistor (TFT) applications have been well refined. Conventional wisdom dictates that removal of excess unbound polymer through filtration or centrifugation is necessary to produce high- erformance TFTs. However, this is time-consuming, wasteful, and resource-intensive. We challenge this paradigm and demonstrate that excess unbound polymer during semiconductor film fabrication is not necessarily detrimental to device performance.[2] With focus on further improving device performance, we look to green, compostable dielectrics to pair with SWCNTs. We report a tri-layer dielectric using poly (lactic acid) (PLA), poly(vinyl alcohol)/cellulose nanocrystals (PVAc) and toluene diisocyanate terminated poly(caprolactone) (TPCL) which we integrated into SWCNT based TFTs in a top gate bottom contact architecture. The PVA provides a high dielectric constant due to the hydroxy groups, the cellulose is used to optimize the viscosity, the TPCL layer provides a robust hydrophobic surface[3], and the PLA eliminates the interfacial charge traps present in the PVAc. This leads to a decrease in leakage currents and reduced the polarity at the dielectric/semiconductor interface. The TFTs fabricated using tri-layer dielectrics led to air stable and balanced hole and electron mobilities which was not observed for the PVAc/TPCL bilayer systems with supressed hole mobility. These TFTs were then used to study the impact of electrochemical doping on the performance of sc-SWCNT TFTs when switching from n-type, where an electrical double layer is formed, to p-type, where the TFSI anions are free to interact with the sc-SWCNTs.[4]The following presentation will focus on the engineering of sc-SWNTs based electronic devices. The choice of conjugated wrapping polymer, dielectric and processing conditions on film formation and the TFT device performance.

Interfacial Engineering of Two-Dimensional Metal–Organic Framework Thin Films for Biomimetic Photoadaptative Sensors

Interfacial Engineering of Two-Dimensional Metal–Organic Framework Thin Films for Biomimetic Photoadaptative Sensors

Fabrication of Large‐Area Organic Thin Film Transistor Array with Highly Uniform Water‐Borne Polyimide Gate Dielectric via Green Solvent‐Engineered Bar‐Coating Process

AbstractHere, the utilization of a highly uniform water‐borne polyimide (W‐PI) thin film as a gate dielectric layer for large‐scale organic thin film transistors (OTFTs) exceeding 100 cm2 is presented, employing the bar‐coating technique. The W‐PI thin films are obtained uniformly over a large area by systematically manipulating the surface tension of the water‐soluble poly(amic acid) salts (W‐PAAS) solution using alcohol as a co‐solvent in a “Green” process. The thickness of the W‐PI thin film is precisely controlled within the range of tens to hundreds of nanometers by adjusting key parameters, including the concentration of the W‐PAAS solution, wire diameter, and bar‐coating speed. As a result, 500 pentacene‐based OTFTs are successfully fabricated on a 10 × 10 cm2 substrate, utilizing a 280 nm thick W‐PI gate dielectric film. These devices exhibit excellent uniformity, with field‐effect mobility of 0.20 ± 0.02 cm2 V−1 s−1. Furthermore, the fabrication of electronic devices using an environmental‐friendly bar‐coating method on large‐area flexible substrates is demonstrated. This study highlights the considerable potential of eco‐friendly W‐PI thin films as dielectric materials, offering advantages such as cost‐effectiveness and high efficiency for reliable industrial applications.

Characterization of tyrosine ammonia lyases from Flavobacterium johnsonian and Herpetosiphon aurantiacus.

p-Coumaric acid (pCA) can be produced via bioprocessing and is a promising chemical precursor to making organic thin film transistors. However, the required tyrosine ammonia lyase (TAL) enzyme generally has a low specific activity and suffers from competitive product inhibition. Here we characterized the purified TAL variants from Flavobacterium johnsoniae and Herpetosiphon aurantiacus in terms of their susceptibility to product inhibition and their activity and stability across pH and temperature via initial rate experiments. FjTAL was found to be more active than previously described and to have a relatively weak affinity for pCA, but modeling revealed that product inhibition would still be problematic at industrially relevant product concentrations, due to the low solubility of the substrate tyrosine. The activity of both variants increased with temperature when tested up to 45°C, but HaTAL1 was more stable at elevated temperature. FjTAL is a promising biocatalyst for pCA production, but enzyme or bioprocess engineering are required to stabilize FjTAL and reduce product inhibition.

Effect of molecular concentration on excitonic nanostructure based refractive index sensing and near-field enhanced spectroscopy

Organic thin film based excitonic nanostructures are of great interest in modern resonant nanophotonics as a promising alternative for plasmonic systems. Such nanostructures sustain propagating and localized surface exciton modes that can be exploited in refractive index sensing and near-field enhanced spectroscopy. To realize these surface excitonic modes and to enhance their optical performance, the concentration of the excitonic molecules present in the organic thin film has to be quite high so that a large oscillator strength can be achieved. Unfortunately, this often results in a broadening of the material response, which might prevent achieving the very goal. Therefore, systematic and in-depth studies are needed on the molecular concentration dependence of the surface excitonic modes to acquire optimal performance from them. Here, we study the effect of molecular concentration in terms of oscillator strength and Lorentzian broadening on various surface excitonic modes when employed in sensing and spectroscopy. The optical performance of the modes is evaluated in terms of sensing, like sensitivity and figure of merit, as well as near-field enhancement, like enhancement factor and field confinement. Our numerical investigation reveals that, in general, an increase in oscillator strength enhances the performance of the surface excitonic modes while a broadening degrades that as a counteracting effect. Most of all, this demonstrates that the optical performance of an excitonic system is tunable via molecular concentration unlike the plasmonic systems. Moreover, different surface excitonic modes show different degrees of tunability and equivalency in performance when compared to plasmons in metals (silver and gold). Our findings provide crucial information for developing and optimizing novel excitonic nanodevices for contemporary organic nanophotonics.

Flexible Organic Transistors for Biosensing: Devices and Applications.

Flexible and stretchable biosensors can offer seamless and conformable biological-electronic interfaces for continuously acquiring high-fidelity signals, permitting numerous emerging applications. Organic thin film transistors (OTFTs) are ideal transducers for flexible and stretchable biosensing due to their soft nature, inherent amplification function, biocompatibility, ease of functionalization, low cost, and device diversity. In consideration of the rapid advances in flexible-OTFT-based biosensors and their broad applications, herein, a timely and comprehensive review is provided. It starts with a detailed introduction to the features of various OTFTs including organic field-effect transistors and organic electrochemical transistors, and the functionalization strategies for biosensing, with a highlight on the seminal work and up-to-date achievements. Then, the applications of flexible-OTFT-based biosensors in wearable, implantable, and portable electronics, as well as neuromorphic biointerfaces are detailed. Subsequently, special attention is paid to emerging stretchable organic transistors including planar and fibrous devices. The routes to impart stretchability, including structural engineering and material engineering, are discussed, and the implementations of stretchable organic transistors in e-skin and smart textiles are included. Finally, the remaining challenges and the future opportunities in this field are summarized.

Monolayer organic thin films as particle-contamination–resistant coatings

Three organic monolayers coatings were developed and tested for their effectiveness to increase cleaning efficiency of attached microscale particles by air flows. The experiments were performed using silica substrates coated with these organic thin films and subsequently exposed to stainless-steel and silica microparticles as a model of contamination. Laser-induced–damage tests confirmed that the coatings do not affect the laser-induced–damage threshold values. The particle exposure results suggest that although the accumulation of particles is not significantly affected under the experimental conditions used in this work, the coated substrates exhibit significantly improved cleaning efficiency with a gas flow. A size-distribution analysis was conducted to study the adsorption and cleaning efficiency of particles of different sizes. It was observed that larger size (> 5-μm) particles can be removed from coated substrates with almost 100% efficiency. It was also determined that the coatings improve the cleaning efficiency of the smaller particles (≤ 5 μm) by 17% to 30% for the stainless steel metal and 19% to 38% for the silica particles.

Development of solar radiation measurement sensor with added value to promote wide-area solar power prediction technology

In this study, we investigated a scenario where the prediction technology for the total output of distributed photovoltaic power generation over a wide area could be more efficiently disseminated by sharing the costs with society, rather than burdening only specific companies with the costs. To achieve this goal, we not only focused on measuring the amount of solar radiation but also incorporated additional parameters into the solar radiation sensor, which is essential for improving the accuracy of the prediction technology. The fundamental configuration of the developed sensor consists of an organic thin film solar cell (OPV), and the output is utilized to transmit the output data externally. Utilizing the surplus power from the OPV, we examined and produced three types of sensors: 1) a sensor with a CO2 measurement function, 2) a sensor with a mist spray function, and 3) a sensor with a photography function using a drive recorder. As a result, all sensors met the predetermined functions and target specifications.

Enhancement of ammonia gas sensitivity and selectivity by depleted layer of PBTTT-C14/MoS2-QDs heterojunction based thin film transistor

A highly sensitive, room temperature operating ammonia (NH3) gas sensor has been fabricated by using PBTTT-C14/MoS2-QDs heterojunction based organic thin film transistor (OTFT). Thin film of PBTTT-C14/MoS2-QDs has been fabricated by low cost and high yield ‘floating film transfer method’ (FTM). Initially, hydrothermally synthesized MoS2 quantum dots (QDs) were added in PBTTT-C14 polymer to make a composite ink, which was used for film fabrication. This polymer/QDs based film has been used as a channel of a top contact-bottom gated organic thin film transistor. Various concentration of NH3 ranging from 0.5 to 50 ppm has been exposed on the channel to determine the sensitivity and the selectivity of the device. For comparison, a reference OTFT has been fabricated under the same condition by using pristine PBTTT-C14 thin film. It has been observed that the response of the polymer/QDs heterojunction device is ∼ 85 % at 50 ppm which is ∼ 3 times higher compared to reference device in higher concentration range of NH3. This enhancement becomes possible due to the NH3 sensitive depletion layer of polymer/QDs heterojunction. This OTFT sensor shows high selectivity to the NH3 gas with good linearity to the concentration, which can fulfill basic requirements for practical utilization.

Thiophene-based thin films with tunable red photoluminescence

Organic thin films with tunable optical properties underlie optical sensors and optoelectronic devices. Here we report on the synthesis of thin films based on thiophene molecular crystals (MC) by dripping method on temperature-controlled substrates with the use of UV radiation to control the photoluminescence (PL) spectra of the films. We achieve 80 nm red shift of the photoluminescence without degradation of thiophene-based MCs. The obtained scalable organic-based thin films with variable PL can be used as optical sensors of UV light, as well as planar substrates for imaging.

Potential and anion effects on the adsorption of 3′,4′-bis(hexylthio)-2,2′:5′,2′'-terthiophene on Au(1 1 1) electrode characterized by in situ STM

The adsorption of organic molecules on gold electrodes serves as a model to understand the organic/inorganic electrified interface, which is relevant to the study of molecular electronics and organic thin film semiconductors. Our previous study on terthiophene (TT) adsorption on an Au(111) electrode shows that immersing Au(111) crystals in a TT ethanol dosing solution installs an ordered TT adlayer on the sample. The current study addresses the adsorption of 3′,4′-bis(hexylthio)-2,2′:5′,2′'-terthiophene (DTDST), a molecule with a TT backbone attached with two thiolhexyl chains, on an ordered Au(111) electrode. High-quality STM images were obtained to reveal the internal and 2D spatial structures of DTDST admolecules. The potential greatly influenced the organization of DTDST on the ordered Au(111) electrode. Although the pristine DTDST adlayer was disordered, it transformed into ordered Au(111) - (3√3 × 9) and (5√3 × 26) structures after applying a potential more negative than 0 V (vs. Ag/AgCl) in 0.1 M H2SO4 and HClO4, respectively. Shifting the potential more positive than 0.25 V resulted in coadsorption of bisulfate anions and restructuring of the DTDST adlayer. High-quality molecular resolution STM images were collected to reveal the azimuthal orientation of the DTDST admolecule on the Au(111) electrode. The thiolhexyl chains of DTDST admolecules could arrange in such a way that allowed intermolecular van der Waals interactions. Oxidation of adsorbed DTDST molecules to yield oligomers was also revealed by in situ STM.

Charge Concentration Limits the Hydrogen Evolution Rate in Organic Nanoparticle Photocatalysts.

Time-resolved microwave conductivity is used to compare aqueous-soluble organic nanoparticle photocatalysts and bulk thin films composed of the same mixture of semiconducting polymer and non-fullerene acceptor molecule and the relationship between composition, interfacial surface area, charge-carrier dynamics, and photocatalytic activity is examined. The rate of hydrogen evolution reaction by nanoparticles composed of various donor:acceptor blend ratio compositions is quantitatively measured, and it is found that the most active blend ratio displays a hydrogen quantum yield of 0.83% per photon. Moreover, it is found that nanoparticle photocatalytic activity corresponds directly to charge generation, and that nanoparticles have 3× more long-lived accumulated charges relative to bulk samples of the same material composition. These results suggest that, under the current reaction conditions, with ≈3× solar flux, catalytic activity by the nanoparticles is limited by the concentration of electrons and holes in operando and not a finite number of active surface sites or the catalytic rate at the interface. This provides a clear design goal for the next generation of efficient photocatalytic nanoparticles.

Foundations of plasma enhanced chemical vapor deposition of functional coatings

Since decades, the PECVD (‘plasma enhanced chemical vapor deposition’) processes have emerged as one of the most convenient and versatile approaches to synthesize either organic or inorganic thin films on many types of substrates, including complex shapes. As a consequence, PECVD is today utilized in many fields of application ranging from microelectronic circuit fabrication to optics/photonics, biotechnology, energy, smart textiles, and many others. Nevertheless, owing to the complexity of the process including numerous gas phase and surface reactions, the fabrication of tailor-made materials for a given application is still a major challenge in the field making it obvious that mastery of the technique can only be achieved through the fundamental understanding of the chemical and physical phenomena involved in the film formation. In this context, the aim of this foundation paper is to share with the readers our perception and understanding of the basic principles behind the formation of PECVD layers considering the co-existence of different reaction pathways that can be tailored by controlling the energy dissipated in the gas phase and/or at the growing surface. We demonstrate that the key parameters controlling the functional properties of the PECVD films are similar whether they are inorganic- or organic-like (plasma polymers) in nature, thus supporting a unified description of the PECVD process. Several concrete examples of the gas phase processes and the film behavior illustrate our vision. To complete the document, we also discuss the present and future trends in the development of the PECVD processes and provide examples of important industrial applications using this powerful and versatile technology.

Transparent and conformable organic light-emitting diodes for skin-attachable invisible displays

A skin-attachable invisible display offers a new opportunity in next-generation electronic application, such as smart contact lenses, human-machine health monitoring interfaces and soft electronic skins. In response to this trend, transparent organic light-emitting diodes (OLEDs) offer enormous advantages in future skin-attachable invisible displays, including excellent flexibility and superior efficiency. Although several approaches reported recently attempt to manufacture transparent and flexible OLEDs, it is still a tremendous challenge to simultaneously meet the desired optical and mechanical properties. Herein, we develop a feasible strategy to achieve transparent and conformable OLEDs (TC-OLEDs). Benefiting from the intrinsic high transparency and outstanding deformability of our electrodes, the whole device shows high transmittance up to 85.0% at a wavelength of 400 nm and high mechanical flexibility with skin-like conformability. More strikingly, the resulting device maintains excellent photoelectric performance with a maximum current efficiency (CE) of 56.8 cd/A and external quantum efficiency (EQE) of 17.1%. Based on the versatile TC-OLEDs, we also report an all-organic and all-conformable invisible display driven by transparent and conformable organic thin film transistors (TC-OTFTs) for the first time. This work offers a meaningful guidance for the construction of TC-OLEDs and the development of skin-attachable invisible displays.