High Average Transmittance Research Articles

Morphology-dependent optical and wetting behavior of GLAD PTFE thin films

E-beam evaporation equipped with glancing angle deposition arrangement (GLAD) was used to fabricate nanostructured polytetrafluoroethylene (PTFE) films in a single-step coating process. Three sets of PTFE coatings were prepared using various oblique angles, e-beam currents, and deposition times to explore the effects of deposition parameters on the properties of PTFE nanostructured coatings. Water contact angle (WCA) of the coatings was found to be enhanced with the increase in all the above process parameters. Optical transmittance of the coatings was also found to be improved with the above parameters except for in the case of an increase in thickness of the films (in very high thickness region), where the transmittance was degraded due to light scattering from the sample surface. After all the optimizations, the ~ 130-nm-thick GLAD PTFE sample prepared with highest e-beam current was found to be more suitable for antireflection and self-cleaning applications. The single-sided coating demonstrates a very high average transmittance of ~ 95.6% (with a wideband transmittance spectrum among the others) in the visible and NIR wavelength range with excellent self-cleaning nature (WCA ~ 156°, sliding angle ~ 10°). The trend of measured WCA with respect to surface roughness follows the Cassie–Baxter model. Overall, the study demonstrates the possibility of fabricating highly transparent self-cleaning coatings using the GLAD technique, which is potentially useful for fabricating protecting cover glasses in solar panels.

Transparent near-infrared perovskite light-emitting diodes

Mobile and wearable devices are increasingly reliant on near-infrared (NIR) covert illumination for facial recognition, eye-tracking or motion and depth sensing functions. However, these small devices offer limited spatial real estate that is typically already occupied by their full-area electronic color displays. Here, we report a transparent perovskite light-emitting diode (LED) that could be overlaid across a color display to provide an efficient and high-intensity NIR illumination. Our transparent devices are constructed with an ITO/AZO/PEIE/FAPbI3/poly-TPD/MoO3/Al/ITO/Ag/ITO architecture, and offer a high average transmittance of more than 55% across the visible spectral region. In particular, our Al/ITO/Ag/ITO top transparent electrode was designed to offer a combination low sheet resistance and low plasma damage upon electrode deposition. The devices emit at 799 nm with a high total external quantum efficiency of 5.7% at a current density of 5.3 mA cm−2 and a high radiance of 1.5 W sr−1 m−2, and possess a large functional device area of 120 mm2. The efficient performance is ideal for battery-powered wearable devices, and could enable advanced security and sensing features on future smart-watches, phones, gaming consoles and augmented or virtual reality headsets.

Transparent Hole-Transporting Frameworks: A Unique Strategy to Design High-Performance Semitransparent Organic Photovoltaics.

Thanks to the nature of molecular orbitals, the absorption spectra of organic semiconductors are not continuous like those in traditional inorganic semiconductors, which offers a unique application of organic photovoltaics (OPVs): semitransparent OPVs. Recently, the exciting progress of materials design has promoted the development of semitransparent OPVs. However, in the perspective of device engineering, almost all reported works reduce the thickness of back/reflected electrode to obtain high average visible transmittance (AVT), which is a trade-off between power conversion efficiency (PCE) and the transmittance of the whole solar spectrum (visible and infrared), and therefore limit the further development. Herein, a unique strategy of "transparent hole-transporting frameworks" is proposed. A hole-transporting large-bandgap polymer (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA)) is employed to partially replace polymer donors in the active layer of PBDB-T/Y1. PTAA is a p-type polymer with a large bandgap of 2.9eV; the partial substitution of PBDB-T by PTAA reduces the absorption of the active layer only in the visible region, keeping the hole-transporting pathways as well as the optimized film morphology. As a result, semitransparent OPVs with PCEs of 12% and AVTs of 20% are achieved, both on rigid and flexible substrates. To demonstrate the generality, this strategy is also used in three different active layers.

Spherical-chain silica with super-hydrophobic surface and ultra-low refractive index for multi-functional broadband antireflective coatings

We present a new type of ultra-low refractive index antireflective (AR) coating based on spherical-chain silica particle with super-hydrophobic surface. This AR coating is fabricated using methyltriethoxysilane (MTES) and ethylsilicate (TEOS) as co-precursors to direct silica particles to form a spherical-chain structure. Then hexamethyldisilazane (HMDS) was further used to modify the surface of spherical-chain silica particle, which greatly decreases the refractive index of the silica thin film from 1.139 to 1.098. The formation mechanism of the ultralow refractive index thin film is proposed. The spherical-chain silica particle surface modification with HMDS significantly improves the hydrophobicity of the coated film; the water contact angle of the film increases from 42° to 168°. Ultimately, using this hydrophobic ultralow-index coating as a top-layer, a high-performance double-layer antireflective coating was fabricated with self-cleaning, environmental resistance and a high average transmittance of 99.64% in the wavelength range of 400–800 nm. This multi-functional broadband antireflective coating has potential value in the field of solar cells.

Ultralow Water Permeation Barrier Films of Triad a-SiNx:H/n-SiOxNy/h-SiOx Structure for Organic Light-Emitting Diodes.

Organic electronic devices such as organic light-emitting diodes (OLEDs), quantum dot LEDs, and organic photovoltaics are promising technologies for future electronics. However, achieving long-term stability of organic-based optoelectronic devices has been regarded as a crucial problem to be solved. In this work, a simple and reproducible fabrication method for ultralow water permeation barrier films having a triple-layered (triad) hydrogenated silicon nitride (a-SiNx:H)/nanosilicon oxynitride (n-SiOxNy)/hybrid silicon oxide (h-SiOx) multistructure is presented. Two triad (a-SiNx:H/n-SiOxNy/h-SiOx)n=2 multistructure barrier films are deposited on both sides of a poly(ethylene terephthalate) substrate using a combination of low-pressure plasma-enhanced chemical vapor deposition and dip coating. The deposited films show a high average transmittance (400-700 nm) of 84% and an ultralow water vapor transmission rate of 2 × 10-6 g/m2/day. In the electroluminescence characteristics of OLEDs encapsulated with two triad barrier films, the operational lifetime (T50) of OLEDs is 1584 h, which is almost similar to that (1416 h) of OLEDs encapsulated with a glass lid.

Fabrication of mesoporous double-layer antireflection coatings with near-neutral color and application in crystalline silicon solar modules

Single-layer antireflection (SLAR) coatings have been applied in crystalline silicon solar modules for a decade, which evolved from open-pore silica at an early stage into closed-pore structures nowadays in industry. For improving photovoltaic and aesthetic characteristics of solar modules, not only AR properties but also color neutrality of AR coatings need to be intensively studied. In this work, the double-layer antireflection (DLAR) coatings were designed and their residual color was studied by comparing with conventional SLAR and DLAR coatings under both normal and oblique incidences. According to the design, we fabricated the mesoporous DLAR coatings, which exhibited a high average transmittance of Tave = 99.02% at visible wavelengths from 380 nm to 780 nm and a low chroma value of C = 3.35. Applying the mesoporous DLAR coatings to the crystalline silicon mini-modules, the power conversion efficiency was increased by 2.40% on average in relative terms. Besides the power output gain, durable DLAR coatings with neutral color are of great significance for not only imparting a natural and sheer-black appearance to photovoltaic modules without unwanted blueish color, but also finding practical applications in consumer electronics, building glazing, and display windows.

Optimization of physical properties of transparent conductive F and Ga co-doped ZnO films for optoelectronic applications

Highly transparent conductive F and Ga co-doped ZnO films were deposited on a glass substrate with radio frequency magnetron sputtering at various growth temperatures. Growing the films at a substrate temperature of 480 °C produced the lowest resistivity of 6.84 × 10−4 Ωcm, a carrier concentration of 2.3 × 1020 cm−3, and a mobility of 39.7 cm2/Vs. These parameters were significantly improved to 3.53 × 10−4 Ωcm, 3.08 × 1020 cm−3, and 57.5 cm2/Vs, respectively, after a rapid thermal annealing treatment. All the films showed a high average transmittance of 90% in the optical range 380–1400 nm.

Reversibly Erasable Broadband Omnidirectional Antireflection Coatings Inspired by Inclined Conical Structures on Blue-Tailed Forest Hawk Dragonfly Wings

Blue-tailed forest hawk dragonfly (Orthetrum triangulare) wings, covered with inclined conical structures, are studying for their high transparency and low reflectance for large viewing angles. However, limited by existing technologies, the exquisite inclined structures are not replicated easily or applied adequately. Here, we combine a shear-induced self-assembly approach and a colloidal lithography technology to create omnidirectional antireflection structures that inspired by dragonfly wings. Non-close-packed colloid crystals are spin-coated and serve as structural templates in a plasma etching procedure to pattern subwavelength inclined conical structures directly on shape memory polymer-coated substrates. The dependence of the antireflection functionality on the shape and inclination of conical structures is systematically investigated in this research. Compared with a featureless substrate, the structure-covered substrate can display a approximately 8% higher average transmittance in the visible wavelength range at normal incidence and even approximately 23% higher average transmittance as the incident angle increases to 75o. Moreover, the reconfigurable structures composed of shape memory polymers can be repeatedly deformed and recovered as a result of external stimuli at ambient conditions, and the corresponding broadband omnidirectional antireflection functionality is therefore reversibly erased and restored.

Cerium-doped indium oxide transparent electrode for semi-transparent perovskite and perovskite/silicon tandem solar cells

Perovskite and perovskite/silicon tandem solar cells hold great promise for commercialization for their high efficiency and low cost. One of the major challenges for semi-transparent perovskite and tandem devices is the availability of suitable transparent electrodes. Here, we report an alternative high-performance cerium-doped indium oxide (ICO) transparent electrode with high mobility, low carrier concentration and high transmittance by Radio frequency (RF) magnetron sputtering at room temperature (RT) for thus applications. A high mobility of 51.6 cm2/Vs, a low resistivity of 5.74 × 10−4 Ω cm as well as a high average transmittance of 83.5% ranging from 400 nm to 1800 nm were obtain at RT. The spectral response of a planar semi-transparent perovskite solar cell (ST-PSC) proportion accelerated in 450–700 nm range and resulted in an absolute 1.1 mA/cm2 (from 17.38 to 18.48 mA/cm2) and 1.47 mA/cm2 (from 13.63 to 15.10 mA/cm2) short-circuit current improvement by replacing commercial ITO electrodes with ICO at different illuminate sides. Finally, the preliminary perovskite/silicon-heterojunction (SHJ) two-terminal tandem solar cell achieves a relative 8.06% improvement in power conversion efficiency (PCE) (from 18.85% to 20.37%) in the use of ICO transparent electrode, illustrating a promising alternative transparent electrode to further improve high-efficiency semi-transparent perovskite and its tandem solar cells.

Semitransparent Perovskite Solar Cells with Dielectric/Metal/Dielectric Top Electrodes

A semitransparent perovskite solar cell (PSC) with a dielectric/metal/dielectric (DMD) multilayer film as the top transparent electrode is investigated. Through adjusting the thickness and the deposition rate of Ag and WO3 layers, a transparent electrode with a low sheet resistance of 7 Ω sq−1 and high average visible transmittance (AVT) of 73% in the visible wavelength range of 400–800 nm is obtained. Using the resultant DMD film as the top transparent electrode and different bandgap perovskites of CH3NH3PbI3 (MAPbI3), CH(NH2)2PbI3 (FAPbI3), and FA0.5MA0.38Cs0.12PbI2.04Br0.96 as the optical active layer, a solar cell with a device architecture of ITO/SnO2/perovskite/spiro‐OMeTAD/MoO3/Ag/WO3 is fabricated. A series of efficient semitransparent PSCs with high transmittance are achieved.

Structure, optical and electrical properties of Nb-doped ZnO transparent conductive thin films prepared by co-sputtering method

Nb-doped ZnO thin films were fabricated on glass substrates by using co-sputtering with direct-current and radio frequency magnetron sputtering. The structures, optical and electrical performances of Nb-doped ZnO thin films were investigated. The results showed that all thin films have (0 0 2) [Formula: see text]-axis preferential orientation. The minimum resistivity of [Formula: see text][Formula: see text]cm and the maximum carrier concentration of [Formula: see text][Formula: see text][Formula: see text] were obtained at the direct-current sputtering power of 10[Formula: see text]W, respectively. Nb-doped ZnO thin films have also shown high average transmittance of 89.6%, and lower surface roughness of 2.74[Formula: see text]nm. Meanwhile, a distinct absorption edge in the ultraviolet range of 300–400[Formula: see text]nm was observed in absorbance, the optical band gap of Nb-doped ZnO thin films illustrates an increased tendency with increasing Nb concentration.

Improved optoelectronic properties of Gd doped cadmium oxide thin films through optimized film thickness for alternative TCO applications

Transparent and conducting thin films of pure and gadolinium(Gd) doped cadmium oxide (CdO) were deposited on glass substrates by RF magnetron sputtering at ambient temperature to develop indium free, alternate transparent conducting electrode for optoelectronic devices. The impacts of Gd doping and film thickness on physical properties of the deposited films were investigated. Mechanism of transmittance, conduction and the scattering process were also discussed. The films showed cubic structure with predominant orientation along (111) plane. All the deposited films were smooth and homogeneous with decreasing roughness from 2.23 nm to 1.69 nm for Gd doped CdO thin film. Pristine CdO film showed peculiar morphology of nano pyramidal shaped grains on the surface. The average transmittance of the films increased from 79% to 88% with the doping of Gd. The Gd doped CdO (GCO) film at a thickness of 900 nm exhibits a maximum transmittance of 93% in visible range. The Gd doped CdO film deposited at a thickness of 900 nm showed the best optoelectronic properties with high average transmittance (88%) and low resistivity (7.203 × 10−5 Ω cm). This result indicates that the Gd doped CdO thin films deposited with suitable thickness can be used as an alternative for high performance TCO in various optoelectronic devices.

A relatively wide-bandgap and air-stable donor polymer for fabrication of efficient semitransparent and tandem organic photovoltaics

Organic photovoltaics (OPVs) have attracted tremendous attention in the field of thin-film solar cells due to their wide range of applications, especially for semitransparent devices. Here, we synthesize a dithiaindacenone-thiophene-benzothiadiazole-thiophene alternating donor copolymer named poly{[2,7-(5,5-didecyl-5H-1,8-dithia-as-indacenone)]-alt-[5,5-(5',6'-dioctyloxy-4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]} (PDTIDTBT), which shows a relatively wide bandgap of 1.82 eV, good mobility, and high transmittance and ambient stability. In this work, we fabricate an OPV device using monolayer graphene as top electrode. Due to the stability of PDTIDTBT in air and water, we use a wet transfer technique for graphene to fabricate semitransparent OPVs. We demonstrate OPVs based on the PDTIDTBT:Phenyl-C61/71-butyric acid methyl ester (PCBM) blend with maximum power conversion efficiencies (PCEs) of 6.1 and 4.75% using silver and graphene top electrodes, respectively. Our graphene-based device shows a high average visible transmittance (AVT) of 55%, indicating the potential of PDTIDTBT for window application and tandem devices. Therefore, we also demonstrate tandem devices using the PDTIDTBT:Phenyl-C61-butyric acid methyl ester (PC60BM) blend in both series and parallel connections with average PCEs of 7.3 and 7.95%, respectively. We also achieve a good average PCE of 8.26% with an average open circuit voltage (Voc) of 1.79 V for 2-terminal tandem OPVs using this blend. Based on tandem design, an OPV with PCE of 6.45% and AVT of 38% is demonstrated. Moreover, our devices show improved shelf life and ultraviolet (UV) stability (using CdSe/ZnS core shell quantum dots [QDs]) in ambient with 45% relative humidity.

An experimental analysis of the optical, thermal and power to weight performance of plastic and glass optics with AR coatings for embedded CPV windows

A low concentrator photovoltaic is presented and the optical losses within a double glazed window assembly are described. The use of plastic instead of glass is analyzed for its reduced weight and hence greater power to weight ratios. Although the transmittance of glass is higher, the power to weight ratio of the plastic devices was almost double that of the glass counterparts and even higher than the original non concentrating silicon cell. The plastic Topas material was found to be the best performing material overall. Crystal Clear, a plastic resin, had a higher average transmittance but had a lower optical efficiency due to the cold cast manufacturing process in comparison to injection moulding of the other materials. This proves the importance of considering both the materials and their associated manufacturing quality.External quantum efficiencies, optical properties, silicon cell temperatures and performance is analyzed for concentrating photovoltaic devices made of varying optical materials. The measurement methods for optical analysis are given in an attempt to separate the optical losses experimentally. The Silicon cells were found to gain higher temperatures due to the insulating plastic optics in comparison to glass but these effects are eliminated during vertical window orientation where instead the encapsulate dominates the insulation of the cell. The results presented here prove plastic optics to be a worthwhile alternative to glass for use in low concentration photovoltaic systems and have the significant effect of reversing the weight disadvantage concentrator photovoltaic technology has compared to standard flat plate solar panels.

Influence of indium and hydrogen co-doping on optical and electrical properties of zinc oxide thin films deposited by DC magnetron sputtering

Introduction: ZnO-based thin films, known as potential transparent-conducting oxides (TCO), have still attracted much attention in applications for good-performance electrodes and inner layers in solar cells. Recently, the research tendency has focused on improving carrier mobility rather than carrier concentration to enhance performance and response speed of TCO thin films. In this work, Indium, and Hydrogen co-doped ZnO (HIZO) thin films were deposited by using DC magnetron sputtering technique in hydrogen-plasma atmosphere.
 Methods: Indium-doped ZnO ceramics were used as sputtering targets, in which, Indium content varied from 0.07 to 1.0 at.%. The electrical, optical, structural and surface morphological properties of the as-deposited films were investigated by using Hall effect-based measurement, UV-Vis spectra, X-ray diffraction (XRD) and fieldemission scanning electron microscopy (FE-SEM), respectively.
 Results: As a result, the HIZO films sputtered from the 0.1 at.% In-doped ZnO target and at H2/(H2+Ar) ratio of 3.5% exhibit high electron mobility (47 cm2/Vs), the lowest resistivity (4.9x10-4 Ω.cm) and sheet resistance (4.7 Ω/sq.), simultaneously, high average transmittance (>80%) in the visible – near IR spectrum regions.
 Conclusion: Based on these results, the HIZO films are considered as potential TCO thin films that can be well-used as transparent electrodes in solar cells.

Tungsten-Doped VO2/Starch Derivative Hybrid Nanothermochromic Hydrogel for Smart Window.

Highly efficient energy-saving windows with high solar modulation properties (ΔTsol) are the everlasting pursuit of research for industrial applications in the smart window field. Hybridization is an effective means of improving both ΔTsol and luminous transmittance (Tlum). In this paper, hybrid thermochromic films were synthesized using tungsten-doped VO2 nanoparticles (NPs) and starch derivatives. Thermoresponsive 2-hydroxy-3-butoxypropyl starch (HBPS) was prepared with a low critical solution temperature (LCST) varying from 32 to 21 °C by the substitution of reactive groups. The hybrid film was obtained by dispersing W-doped VO2 NPs in HBPS hydrogels, which exhibiting remarkable solar modulation property (ΔTsol = 34.3%) with a high average luminous transmittance (Tlum, average = 53.9%).

Role of zinc interstitial defects in indium and magnesium codoped ZnO transparent conducting films

Transparent conducting In and Mg codoped ZnO (IMZO) thin films were deposited on quartz substrates at room temperature by radio frequency magnetron sputtering. The influence of Mg concentration (from 0 to 6 at.%) on the structural, optical and electrical properties of IMZO thin films was investigated in detail. All IMZO thin films have typical hexagonal wurtzite structure with a preferential orientation along the c-axis and show high average optical transmittance above 85% in the visible region. And, the optical band gap is tunable with the addition of the Mg dopants. The presence of indium favors energetically the formation of abundant zinc interstitial (Zni) related shallow donor defects, thus greatly increasing the carrier concentration in the film. However, it was found that the electrical conductivity decreased as the Mg content increased. The main origin is related to the density reduction of Zni-related defects. Furthermore, the electrical properties of IMZO thin films can be significantly improved by thermal diffusion of extrinsic Zn atoms which creates extra Zni-related defects that provide electron carriers. These efforts will facilitate the development of ZnO-based TCO thin films.

High transmittance β-Ga2O3 thin films deposited by magnetron sputtering and post-annealing for solar-blind ultraviolet photodetector

Monoclinic Ga2O3 (β-Ga2O3) thin films were deposited on c-plane sapphire substrates via radio frequency magnetron sputtering method followed by post-annealing process. The structural and optical properties of β-Ga2O3 films deposited at various sputtering powers were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible (UV–Vis) spectrophotometer and X-ray photoelectron spectroscopy (XPS). The results show that all the films are pure β-Ga2O3 with single (2¯01) preferred orientation. The growth rate of the films increases linearly with increasing the sputtering power, which directly results in β-Ga2O3 film deposited at a high sputtering power having the relatively high crystal quality and flat surface structure. All the β-Ga2O3 films exhibit extremely high average transmittance of 95% in UV–Vis light with wavelength above 300 nm, and the lower the sputtering power, the larger the bandgap of the β-Ga2O3 film due to the Al diffusion from the substrates. A metal-semiconductor-metal (MSM) structured solar-blind photodetector based β-Ga2O3 film with optimal structural and optical properties was fabricated, and excellent solar-blind ultraviolet characteristics were demonstrated. The photodetector has a high Iphoto/Idark ratio (>103) along with the response time (0.31 s) and decay time (0.05 s), indicating that the β-Ga2O3 film deposited by sputtering method followed by post-annealing can have great potential for fabricating fast response solar-blind ultraviolet photodetectors.

Solution-Processed Semitransparent Organic Photovoltaics: From Molecular Design to Device Performance.

Recent research efforts on solution-processed semitransparent organic solar cells (OSCs) are presented. Essential properties of organic donor:acceptor bulk heterojunction blends and electrode materials, required for the combination of simultaneous high power conversion efficiency (PCE) and average visible transmittance of photovoltaic devices, are presented from the materials science and device engineering points of view. Aspects of optical perception, charge generation-recombination, and extraction processes relevant for semitransparent OSCs are also discussed in detail. Furthermore, the theoretical limits of PCE for fully transparent OSCs, compared to the performance of the best reported semitransparent OSCs, and options for further optimization are discussed.

Impacts of the thickness on the electron mobility of gallium and hydrogen co– doped zinc oxide thin films

this work, impacts of the thickness on electron mobility of Ga and H2 co-doped ZnO (HGZO) thin films were investigated. The HGZO films were prepared on glass substrate by using magnetron sputtering from ceramic Ga-doped ZnO (GZO) target in the gas mixture of argon and hydrogen. Based on the Hall measurement, the mobility enhanced fastly from 44.6 to 53.4cm2/Vs with the increasing thickness from 350 to 900 nm, then tends to be saturated at ~55cm2/Vs with further thickness. Most of the films achieve the mobility of >50cm2/Vs, which is very high value for sputtered TCOs thin films. The thicknessdependent mobility is explained in term of grain boundary scattering. The improvement of crystalline quality reduced grain boundary scattering, which lead to the fast increase in mobility of the films with 350–900nm in thickness. When the thickness increased more than 900nm, however, the appearance of many defects increased scattering centers and saturates the mobility. Furthermore, the results showed the HGZO films with optimum thickness of 800nm obtained low resistivity (5.3 10-4􀁛cm), high average transmittance (83.3%) in the wide wavelength range of 400–1100nm, and the highest figure of merit (10.3 103􀁛-1cm-1) corresponding to high mobility (51.1cm2/Vs).