Optical Transparency Properties Research Articles

Microbubble-Triggered Spontaneous Separation of Transparent Thin Films from Substrates Using Evaporable Core-Shell Nanocapsules.

The spontaneous separation of a polymer thin film from a substrate is an innovative technology that will enable material recycling and reduce manufacturing cost in the film industry, and this can be applied in a wide range of applications, from optical films to wearable devices. Here, we present an unprecedented spontaneous strategy for separating transparent polymer films from substrates on the basis of microbubble generation using nanocapsules containing an evaporable material. The core-shell nanocapsules are prepared from poly(methyl methacrylate)-polyethyleneimine nanoparticles via the encapsulation of methylcyclohexane (MCH). A spherical nanostructure with a vaporizable core is obtained, with the heat-triggered gas release ability leading to the formation of microbubbles. Our separation method applied to transparent polymer films doped with a small amount of the nanocapsules encapsulating evaporable MCH enables spontaneous detachment of thin films from substrates via vacuum-assisted rapid vaporization of MCH over a short separation time, and clear detachment of the film is achieved with no deterioration of the inherent optical transparency and adhesive property compared to a pristine film.

CuI p-type thin films for highly transparent thermoelectric p-n modules

Developments in thermoelectric (TE) transparent p-type materials are scarce and do not follow the trend of the corresponding n-type materials – a limitation of the current transparent thermoelectric devices. P-type thermoelectric thin films of CuI have been developed by three different methods in order to maximise optical transparency (>70% in the visible range), electrical (σ = 1.1 × 104 Sm−1) and thermoelectric properties (ZT = 0.22 at 300 K). These have been applied in the first planar fully transparent p-n type TE modules where gallium-doped zinc oxide (GZO) thin films were used as the n-type element and indium thin oxide (ITO) thin films as electrodes. A thorough study of power output in single elements and p-n modules electrically connected in series and thermally connected in parallel is inclosed. This configuration allows for a whole range of highly transparent thermoelectric applications.

Preparation and characterization of poly dimethylsiloxane based on polyurethane hydrogels with interpenetrating network structure for contact lenses uses

The interpenetrating polymer network (IPN) silicone hydrogels have been synthesized using polydimethylsiloxane- polyurethane- polyethylene glycol methacrylate (PDMS–PU–PEGMA) prepolymer with different concentrations of N,N dimethyl acrylamide (DMA), polyethylene glycol methacrylate (PEGMA) and methacryloxypropyl tris(trimethylsoloxy)silane (TRIS) by UV initiated polymerization process in the presence of free radical photoinitiator. The physicomechanical and chemical properties of the IPN silicone hydrogels, as water content, protein resistance, contact angle, optical transparency and mechanical properties were evaluated. The results revealed that DMA and PEGMA incorporated in IPN silicone hydrogel improves the hydrophilicity of silicone hydrogel with higher optical transparency and better protein resistance ability. The moduli of IPN silicone hydrogels indicate stiffer network as the concentration of PDMS–PU–PEGMA prepolymer increased. IPN silicone hydrogels belong to hydrophilic surfaces with the lowest water contact angle of 48.76o.

A facile approach to prepare porous polyamide films with enhanced electrochromic performance.

Novel electroactive triphenylamine-based polyamide (PA) films with a purposeful porous structure have been designed and prepared by a simple route. Polymer thin films containing well dispersed electrolyte salts were prepared first, then channels of pores could be generated within the polymer film by washing the salts out. With the help of the porous channels, the diffusion rate between electroactive species and the electrolyte during the electrochemical process could be effectively increased. Consequently, the driving potential and electrochromic response time can be efficiently improved through this approach. Novel porous PA films with optimal results both in optical transparency and electrochemical properties could be readily obtained by choosing a commonly used supporting electrolyte TBABF4 as a salt in this study. When the PA films containing un-washed TBABF4 salt were further assembled into electrochromic devices (ECDs), the salt could then be leached out during the electrochemical redox switching process to form a porous film structure and also serves as a supporting electrolyte in ECDs simultaneously. Therefore, EC performance such as the driving potential and response time could be enhanced obviously by this simplified fabrication procedure of ECDs.

Peptide Integrated Optics.

Bio-nanophotonics is a wide field in which advanced optical materials, biomedicine, fundamental optics, and nanotechnology are combined and result in the development of biomedical optical chips. Silk fibers or synthetic bioabsorbable polymers are the main light-guiding components. In this work, an advanced concept of integrated bio-optics is proposed, which is based on bioinspired peptide optical materials exhibiting wide optical transparency, nonlinear and electrooptical properties, and effective passive and active waveguiding. Developed new technology combining bottom-up controlled deposition of peptide planar wafers of a large area and top-down focus ion beam lithography provides direct fabrication of peptide optical integrated circuits. Finding a deep modification of peptide optical properties by reconformation of biological secondary structure from native phase to β-sheet architecture is followed by the appearance of visible fluorescence and unexpected transition from a native passive optical waveguiding to an active one. Original biocompatibility, switchable regimes of waveguiding, and multifunctional nonlinear optical properties make these new peptide planar optical materials attractive for application in emerging technology of lab-on-biochips, combining biomedical photonic and electronic circuits toward medical diagnosis, light-activated therapy, and health monitoring.

Liquid PMMA: A High Resolution Polymethylmethacrylate Negative Photoresist as Enabling Material for Direct Printing of Microfluidic Chips

Polymethymethacrylate (PMMA) is one of the most important thermoplasts and a commonly used material in microsystem fabrication, for example, microfluidics owning mainly to its optical transparency, biocompatibility, low autofluorescence, and low cost. However, being a thermoplastic material PMMA is typically structured using industrial replication techniques making PMMA unsuitable for rapid prototyping. The fact that neither material nor processing technique can be directly transferred from laboratory to industrial state makes the research‐to‐business conversion often extremely difficult in microfluidics since material properties have a major impact on the final system behavior. This paper presents “Liquid PMMA,” a fast curing viscous PMMA prepolymer which can be used as a negative photoresist and directly structured using ultraviolet or visible light with tens of micron resolution and smooth surfaces. Using this technique microfluidic chips in PMMA can be fabricated within minutes. The cured Liquid PMMA parts show the same high optical transparency, low autofluorescence, and surface properties like commercial PMMA. In this way, microfluidic chips can be rapidly developed and optimized on the laboratory scale in the same material which is later on used on the industrial scale.

All cellulose composites based on cellulose diacetate and nanofibrillated cellulose prepared by alkali treatment

Cellulose diacetate (CDA) composite films were synthesized by incorporation of nanofibrillated celluloses (NFCs), using a casting/evaporation technique. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) characterization indicated the presence of interaction and certain compatibility between CDA and NFCs. The CDA and NFCs were converted to cellulose II by an alkaline treatment which resulted in the formation of all cellulose composite (ACC) films, as indicated by the FTIR and XRD characterization. Significant changes were observed in their structural, thermal, mechanical, and optical transparency properties. The SEM images revealed the excellent compatibility among the constituents of the ACC films. The tensile strength, Young’s modulus, and strain at break of the ACC films with 15wt% NFCs content were increased to 102.3MPa, 5.8GPa, 14.7% respectively. This work provides a promising pathway for manufacturing high performance ACC materials.

Ab initio investigations of electronic structure, optical transparency, and elastic properties in X3Al2Si3O12 (X = Ca, Mg)

Abstract A series of ab initio simulations were performed to investigate the electronic, transparent, and elastic properties of Ca 3 Al 2 Si 3 O 12 and Mg 3 Al 2 Si 3 O 12 which have potential applications in lithography optics, lenses and phosphor materials. From the simulated electronic structure and optical properties, we found that the theoretical transmittance of both compounds reaches 90% above 198 nm in the UV region. The bulk modulus and shear modulus of Ca 3 Al 2 Si 3 O 12 were calculated to be 181.41 and 115.84 GPa, respectively. The anisotropy in elastic properties along different crystallographic direction were found greater in Ca 3 Al 2 Si 3 O 12 than that in Mg 3 Al 2 Si 3 O 12 . The distinct dodecahedral coordinated Ca and Mg in the crystal structures result in the maximum Young's modulus existing in different direction, which is along [1 0 0] direction for Ca 3 Al 2 Si 3 O 12 but [1 1 1] direction for Mg 3 Al 2 Si 3 O 12 . Our theoretical investigations provided a basic understanding on the materials design of Ca 3 Al 2 Si 3 O 12 and Mg 3 Al 2 Si 3 O 12 .

Formation of microporous membranes by biaxial orientation of compatibilized PP/Nylon 6 blends

Polymer blends comprising polypropylene, Nylon 6, and a compatibilizer were extruded and biaxially stretched. The as-extruded films with various compositions were characterized in terms of morphology, crystallization behavior, optical transparency, and oxygen barrier property. The blend films with all five compositions presented matrix-dispersed morphology with polypropylene as the continuous phase when the Nylon 6 composition is less than 55 w.t. %. The morphology was reversed when Nylon 6 composition increased to 65 w.t. %. As-extruded films exhibited high optical transparency and good oxygen barrier properties. The blend films were then biaxially, sequentially drawn at 155 °C to draw ratio of 2.5 by 2.5. Stretching of one of the blend films containing 30% polypropylene, 55% Nylon 6, and 15% compatibilizer produced a microporous membrane with through-pore structure. The pore size of such membrane was around 100 nm with a porosity of 52%. Formation of through-pore structure was sensitive to both the composition and the process where blends with less Nylon 6 concentration or lower draw ratio would not yield through-pore structure. The generation of through pores were attributed to cavitation of polypropylene on the polypropylene-Nylon 6 interface.

Quantum and conversion efficiencies optimization of superstrate CIGS thin-films solar cells using In2Se3 buffer layer

In this present contribution, AMPS-1D device simulator is employed to study the performances of superstrate SLG/TCO/p-Cu(In,Ga)Se2(CIGS)/n-ODC/n-In2Se3/Metal thin film solar cells. The impact of the TCO and Metal work functions on the cell performance has been investigated. The combination of optical transparency and electrical property for TCO front contact layer is found to yield high efficiency. The obtained results show that the TCO work function should be large enough to achieve high conversion efficiency for superstrate CIGS solar cell. Nevertheless, it is desirable for Metal back contact layer to have low work function to prevent the effect of band bending in the n-In2Se3/Metal interface. Several TCOs materials and metals have been tested respectively as a front and back contact layers for superstrate CIGS solar cells. An efficiency of 20.18%, with Voc ≈ 0.71 V, Jsc ≈ 35.36 mA/cm2 and FF ≈ 80.42%, has been achieved with ZnSn2O3-based as TCO front contact layer. In the case of SnO2:F front contact and indium back contact layers, an efficiency of 16.31%, with Voc ≈ 0.64 V, Jsc ≈ 31.4 mA/cm2 and FF ≈ 79.4%, has been obtained. The present results of simulation suggest an improvement of superstrate CIGS solar cells efficiency for feasible fabrication.

Highly refractive polyimides containing pyridine and sulfur units: synthesis and thermal, mechanical, solubility and optical properties

AbstractTwo series of isomers containing pyridine and sulfur unit aromatic diamine monomers, 4,4′‐bis(5‐amino‐2‐pyridinylsulfanyl)diphenyl sulfide (2a), 4,4′‐bis(6‐amino‐3‐pyridinylsulfanyl)diphenyl sulfide (2b) and 4,4′‐bis(5‐amino‐6‐methyl‐2‐pyridinylsulfanyl)diphenyl sulfide (2c), 4,4′‐bis(5‐amino‐4‐methyl‐2‐pyridinylsulfanyl)diphenyl sulfide (2d), were designed and synthesized. Aimed at clarifying the structure–property relationships of pyridine‐ and sulfur‐containing high refractive polymers, 2a was polymerized with various dianhydrides to prepare polyimides PI‐1−PI‐7 and 2b, 2c, 2d were reacted with 4,4′‐[p‐thiobis(phenylenesulfanyl)]diphthalic anhydride to prepare polyimides PI‐8−PI‐10. The polyimides showed excellent optical properties with average refractive indices ranging from 1.7006 to 1.7620 and birefringence as low as 0.0056. Meanwhile, comparative studies on their properties including solubility, thermal and mechanical, and optical transparency properties were performed. Some property differences of the isomers caused by the sequence changes were found. © 2017 Society of Chemical Industry

Importance of zwitterionic incorporation into polymethacrylate-based hydrogels for simultaneously improving optical transparency, oxygen permeability, and antifouling properties.

Conventional 2-hydroxyethyl methacrylate (HEMA)-based hydrogels have an inverse relationship between optical transparency (OP) and oxygen permeability (Dk) as a function of water content. While the higher water content favors the oxygen permeability of HEMA-based hydrogels, it also causes poor optical transparency due to the water-induced scattering center effect. Here, we propose and demonstrate that the incorporation of zwitterionic [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA) with HEMA hydrogels enables the achievement of both properties (OP = 98% and Dk = 54.7) in hydrogels at high water contents of 84%, and both values are much higher than those of pure HEMA hydrogels (OP = 2.3% and Dk = 17.5 barriers). HEMA-SBMA hydrogels are crosslinked by electrostatic interactions between the zwitterionic SBMA groups and hydrogen bonds between the HEMA groups. The introduction of SBMA into HEMA not only increases the quantity and quality of strongly binding water inside the networks, but also affects the porous structure of the gels, both of which are correlated with OP and Dk. Moreover, hybrid HEMA-SBMA hydrogels demonstrate their excellent antifouling function to prevent nonspecific protein adsorption in vitro, as well as their biocompatibility and hemocompatibility when implanted in mice in vivo. A combination of these excellent properties of HEMA-SBMA hydrogels (high water content, high optical transparency, high oxygen permeability, good antifouling function, and low foreign-body reaction) makes them highly promising for contact lens-based ophthalmic applications. This work, in line with our other HEMA-CBMA hydrogels, offers a new strategy to design hybrid hydrophilic-zwitterionic materials for improving their multi-faceted properties of interest, beyond the conventional designs of hydrophilic-hydrophilic and hydrophilic-hydrophobic materials.

Highly optical transparency and thermally stable polyimides containing pyridine and phenyl pendant

In order to obtain highly optical transparency polyimides, two novel aromatic diamine monomers containing pyridine and kinky structures, 1,1-bis[4-(5-amino-2-pyridinoxy)phenyl]diphenylmethane (BAPDBP) and 1,1-bis[4-(5-amino-2-pyridinoxy)phenyl]-1-phenylethane (BAPDAP), were designed and synthesized. Polyimides based on BAPDBP, BAPDAP, 2,2-bis[4-(5-amino-2-pyridinoxy)phenyl]propane (BAPDP) with various commercial dianhydrides were prepared for comparison and structure-property relationships study. The structures of the polyimides were characterized by Fourier transform infrared (FT-IR) spectrometer, wide-angle X-ray diffractograms (XRD) and elemental analysis. Film properties including solubility, optical transparency, water uptake, thermal and mechanical properties were also evaluated. The introduction of pyridine and kinky structure into the backbones that polyimides presented good optical properties with 91–97% transparent at 500 nm and a low cut-off wavelength at 353–398 nm. Moreover, phenyl pendant groups of the polyimides showed high glass transition temperatures (Tg) in the range of 257–281 °C. These results suggest that the incorporating pyridine, kinky and bulky substituents to polymer backbone can improve the optical transparency effectively without sacrificing the thermal properties.

Synergistic Effects of Linseed Oil Based Waterborne Alkyd and 3-Isocynatopropyl Triethoxysilane: Highly Transparent, Mechanically Robust, Thermally Stable, Hydrophobic, Anticorrosive Coatings

High-performance vegetable oil based organic–inorganic bio hybrid materials are of great interest in the current scenario, as the utilization of vegetable oil meets the seventh principle out of the 12 Principles of Green Chemistry that contributes to sustainability in chemistry due to their universal availability, inherent biodegradability, low price, and superb environmental credentials. Here, we report the synthesis of transparent organic–inorganic bio hybrid coatings by tailoring the properties of both linseed oil and 3 isocynatopropyl triethoxysilane (IPTES) using the sol–gel technique. Such materials combine the advantages of both the phases that are usually not compatible within the same material (robustness and homogeneity, mechanical strength, flexibility, optical transparency, hydrophobicity, and anticorrosive properties). The structure elucidation, particle size, and morphology of the synthesized OIH polymers were done by FT-IR, 1H NMR, 13C NMR, 29Si NMR, and electron microscopy techniques (TEM ...

Analysis of Sputter-Deposited SnO thin Film with SnO/Sn Composite Target

Tin oxides have been studied for various applications such as gas detecting materials, transparent electrodes, transparent devices, and solar cells. p-type SnO is a promising transparent oxide semiconductor because of its high optical transparency and excellent electrical properties. In this study, we fabricated p-type SnO thin film using rf magnetron sputtering with an SnO/Sn composite target; we examined the effects of various oxygen flow rates on the SnO thin films. We fundamentally investigated the structural, optical, and electrical properties of the p-type SnO thin films utilizing X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis spectrometry, and Hall Effect measurement. A p-type SnO thin film of PO2 = 3 % was obtained with > 80 % transmittance, carrier concentration of 1.12 × 1018 cm−3, and mobility of 1.18 cm2V−1s−1. With increasing of the oxygen partial pressure, electrical conductivity transition from p-type to n-type was observed in the SnO crystal structure.

Reactive polycarbonate/diallyl phthalate blends with high optical transparency, good flowability and high mechanical properties

Bisphenol-A polycarbonate (BAPC) is an important engineering plastic with superior optical and mechanical properties, but it is difficult to be processed due to the high melt viscosity. In this work, the blends of BAPC and reactive plasticizer of diallyl phthalate (DAP) were studied before and after polymerization of DAP using dicumyl peroxide (DCP) as thermal initiator. The morphology evolution and phase transitions of the blends during heating were investigated by polarized optical microscopy equipped with hot stage and differential scanning calorimetry. With raising temperature, the apparent phase transitions, i.e., thermally induced partial phase separation with upper critical solution temperature (UCST) behavior, BAPC cold crystallization, DAP polymerization and BAPC crystal melting, occurred in sequence. Compared to pure BAPC, the BAPC/poly(DAP) blends with 10–15 wt.% of poly(DAP) had good performances, including similar glass transition temperature, tensile strength and ∼80% of optical transmittance in the wavelength range of 600–800 nm, as well as an increase of 64–68% for moduli and 100–135% for melt flow index, respectively. These good performances were attributed to the bicontinuous structure of the blends. This study provides a facile strategy to realize the easy processing for intractable polymers and to maintain, even to enhance the high performances of the original polymers.

An Evaluation of Potential Yield of Indium Recycled from Waste Mobile Phone in China

In recent years, users replace their mobile phone more and more frequently, therefore, the number of waste mobile phones has been increasing year by year. In 2014, the number was more than 1 billion units. Indium, that has unique optical transparency and electrical conduction properties, is a necessary element in the screen of mobile phone. The potential yield of indium recycled from waste mobile phone is considerable. Recycling indium from waste mobile phones can alleviate the constraints of indium resources while gaining great economic benefit. However, there is no relevant research work to evaluate the potential yield of indium in the waste cell phone. This paper explores the main factors that constraint the efficiency of recycling by predicting potential yield of indium recycled from waste mobile phone, and puts forward the corresponding policy recommendations. The results are based on the Logistic model and Stock-base model and a survey. The results show that the potential yield of indium recycled from waste mobile phone from 2015 to 2035 will increase from 8.7 tonnes to 10.2 tonnes in China. However, the recovery rate of waste mobile phone is very low, the actual available amount is far lower than the potential yield of indium. The main factors that constrain the efficiency of recycling are: (1) it is difficult to guarantee information security; (2) the existing recycling system is not perfect; (3) the technology of recycling indium needs to be improved.

Buckling effects on electronic and optical properties of BeO monolayer: First principles study

Using ab initio study, we apply full potential augmented plane waves plus local orbital and generalized gradient approximation for expanding wave functions and exchange–correlation functional term to investigate the electronic and optical properties of beryllium oxide nanosheet. The different values of planar buckling are considered to study. Also the results for fluorinated BeO nanosheet is compared to corresponding non-fluorinated buckled nanosheet. A red-shift in optical spectra is observed obviously as a result of weakening of σ bonds and increasing the number of π electrons. Also optical transparency property for visible range of the electromagnetic spectrum and vanishing energy-band degeneracy is concluded from our data.

Photocurable gelatin hydrogels for cell encapsulation

Event Abstract Back to Event Photocurable gelatin hydrogels for cell encapsulation Timothy Hughes1*, Lingli Li1, 2*, Conglie Lu2*, Mei Chen2*, Huixiang Ma2*, Lei Wang3*, Xiaojuan Hao1*, Keith Mclean1* and Chen Hao2, 3* 1 CSIRO, Manufacturing, Australia 2 Wenzhou Medical University, Wenzhou Eye Hospital, China 3 Wenzhou Institute of Biomaterials and Engineering, China Introduction: Tissue engineering requires the implantation of cells along with a supportive scaffold. As such, degradable support scaffolds that are amenable to minimally invasive implantation are attractive. With this in mind, we have explored the use of phototriggered thiol-ene reactions as a method to produce injectable and photocurable cell supportive scaffolds that can be cured in the presence of cells (Figure 1). Figure 1: Conceptual diagram of in situ cured scaffold in the presence of cells Materials and Methods: Type A Porcine skin (Bloom 100) Gelatin (Sigma Aldrich) was used for experiments. Vinyl functionalised gelatines were produced from gelatine and vinyl anhydrides (eg: acrylate and pentanoic anhydride)[1]. While thiolylated gelatin was prepared from gelatin and cysteine with EDC and NHS[1]. The products were purified by dialysis (1 kDa MWCO) and freeze dried before being reconstituted with saline (0.9 %). Light triggered thiol-ene reactions were used to crosslink the vinyl functionalised gelatins with multifunctional thiols included thiolated gelatin. The rheological properties of the precursor formulations as well as the final gels and their cure profiles were measured using photorheology. The effect of solids content, ratio of components and light intensity were investigated. The water content, optical transparency and mechanical properties and microscopic morphologies of the gels were also measured. The ability of bovine corneal endothelial cells (bCECs) and fibroblast cells (L929) to grow on the gels was investigated. The in situ curing of gels in the presence of living cells was also explored. Finally a gelatin hydrogel was cured in situ to fill corneal defects in rabbits(trephine, 3 mm diameter by 200 μm deep) to assess the corneal biocompatibility of the hydrogels. Results and Discussion: Thiol-ene crosslinked gelatins were able to be cured within 2 min. of exposure to 365 nm light resulting in optically transparent gels with water contents about 80-85 %. The resulting soft gels possessed high viability of both L929 and bCECs (>80 %). The mechanical properties of the gels could be tuned by altering the feed ratio of the components and the light intensity used during the cure. Live/Dead staining confirmed that both bCEC and L929 retained high cell viability in culture following in situ cure of the gelatin hydrogels containing the cells (Figure 2). Moreover, laser confocal imaging indicated that the cells were evenly distributed within the hydrogel. Figure 2: 3D Laser confocal fluorescent imaging of L929 cells pre stained with DilC(3) after 7 days of cell culture in a hydrogel matrix prepared from a formulation of 150 mg/ml 2:1 Gel-LA to Gel-SH + Irgacure 2959 (0.5 %) cured with 100 mW/cm2 for 1min Corneal defects in rabbit corneas were filled with in situ cured gelatine hydrogel and the wounded cornea re-epithelialized in 3 to 7 days with minimal inflammation (Figure 3). Figure 3: Slit lamp microscope images of corneal defects at day 1 (left) and 7 (right) stained with fluorescein filled with gelatin hydrogel matrix prepared from a formulation of 150 mg/ml 2:1 Gel-LA to Gel-SH + Irgacure 2959 (0.5 %) cured with 100 mW/cm2 for 1min Conclusions: Phototriggered thiol-ene reactions are rapid and facile methods of forming crosslinked gelatin hydrogels. They resulted in transparent gels with mechanical properties suitable for soft tissue replacements. In addition, they could be cured in the presence of living cells which maintained high viability for over 7 days post crosslinking. Moreover, the in situ cured gels were able to heal rabbit corneal defects in vivo with low inflammation and rapid re-epithelialization. Therefore, the resulting materials are promising candidates for corneal tissue engineering substrates. This study is supported by Chinese Scholarship Council, the International Scientific and Technological Cooperation Project (No. 2012DFB30020) and High-end Foreign Experts Recruitment Program (China, No.GDW20133300101).

Solution-processed copper oxide interlayers for broadband PbS quantum-dot photodiodes

Metal oxide interlayers are promising for optoelectronic applications due to solution processability, optical transparency, and excellent charge blocking properties.