High Average Transmittance Research Articles

Solution-Processed Mg-Substituted ZnO Thin Films for Metal-Semiconductor-Metal Visible-Blind Photodetectors

The effects of Mg on the microstructural, optical, and electrical properties of sol-gel derived ZnO transparent semiconductor thin films and the photoelectrical properties of photodetectors based on MgxZn1−xO (where x = 0 to 0.3) thin films with the metal-semiconductor-metal (MSM) configuration were investigated in this study. All the as-synthesized ZnO-based thin films had a single-phase wurtzite structure and showed high average transmittance of 91% in the visible wavelength region. The optical bandgap of MgxZn1−xO thin films increased from 3.25 to 3.56 eV and the electrical resistivity of the films rose from 6.1 × 102 to 1.4 × 104 Ω·cm with an increase in Mg content from x = 0 to x = 0.3. Compared with those of the pure ZnO thin film, the PL emission peaks of the MgZnO thin films showed an apparent blue-shift feature in the UV and visible regions. The photo-detection capability was investigated under visible, UVA, and UVC light illumination. Linear I-V characteristics were obtained in these ZnO-based photodetectors under dark and light illumination conditions, indicating an ohmic contact between the Au electrodes and ZnO-based thin films. It was found that the pure ZnO photodetector exhibited the best photoconductivity gain, percentage of sensitivity, and responsivity under UVA illumination. Under UVC illumination, the photoconductivity gain and percentage of sensitivity of the MgZnO photodetectors were better than those of the pure ZnO photodetector.

Nanostructured, ultrathin silver-based transparent electrode with broadband near-infrared plasmonic resonance

A nanostructured transparent electrode with high average visible transmittance of 76%, low sheet resistance of 7.0 Ω/sq and steep transmittance drop in the near-infrared (NIR) range is investigated by simulations and experiments. The electrode is composed of a nanostructured substrate, on which a trilayer, consisting of an ultrathin 14 nm thick silver film embedded between thin films of TiO2 and Al-doped ZnO, is deposited. Directional silver deposition results in the formation of a disk-hole array without additional lift-off or etching steps. While the trilayer approach enables increased visible transmittance, the transmittance in the NIR regime is decreased by a broadband plasmonic dipole excitation in the disk-hole array. Moreover, a rich mode spectrum of weaker multipole surface plasmon excitations is observed in the nanodisk- and nanohole array. The presented electrode holds great potential for applications in optoelectronic devices, solar control coatings and solar cells.

A highly transparent polymer coating on the glass with broadband antireflection, antifogging and antifouling properties

Transparent coatings with the multiple functions of antireflection, antifogging and antifouling can simultaneously solve the three main issues of reflection, fogging and fouling, which can dramatically improve the light efficiency and utilization convenience of optical elements, such as glass. Here, we report that, the multifunctional bionic polymer moth-eye coating can be fabricated on the glass surface by a facile and low-cost method of template-assisted prepolymer curing. The polymer moth-eye arrays can firmly adhere to the glass substrate due to the bonding agent 3-aminopropyl triethoxy silane, which can react with the hydroxy groups of the glass surface and the copolymer, respectively. Due to the high surface energy of the polymer coating, it shows superhydrophilic property and exhibits high average transmittance after fogging for 0 min (98.9%) and 10 min (96.9%) in visible the wavelength range (380–800 nm). It also exhibits ideal repellent to contamination, which still can maintain high transparency (90%) after pulling out from the exemplified graphite powder.

Experimental investigation on spectral splitting of photovoltaic/thermal hybrid system with two-axis sun tracking based on SiO2/TiO2 interference thin film

In a “thermally decoupled” PV/T system, photovoltaic and thermal absorbers are allowed to operate at different temperatures to utilize full-spectrum sunlight. In this study, a two-axis tracking PV/T system with a SiO2/TiO2 interference thin film (irradiated by natural sunlight) was designed and fabricated initially. The SiO2/TiO2 interference thin film designed by the authors achieved a high average reflectance (R ≥ 96.8%) for PV bands, with a high average transmittance (T ≥ 85%) at 1100–2500 nm. The photoelectric, photothermal, and overall efficiencies were tested and analyzed theoretically using the first and second laws of thermodynamics. Outdoor testing indicated that PV cells with SiO2/TiO2 interference thin film can decrease by 3.0 K, and that the power generation and efficiency of the PV cells can be improved by 10% and 0.65%, respectively. The overall energy and exergy efficiency of the PV/T system based on SiO2/TiO2 interference thin film can reach 22.72% and 18.81%, i.e., 4.94% and 1.03% higher than those without a SiO2/TiO2 interference thin film, respectively. The calculated payback time was 17 years for this PV/T system.

Epitaxial ultrathin Au films on transparent mica with oxide wetting layer applied to organic light-emitting devices

Ultrathin and transparent metal films are considered as desirable materials to substitute indium-tin oxide based transparent electrodes. In this work, we report that an Al-doped ZnO layer effectively induced the formation of epitaxial ultrathin and ultrasmooth Au films on mica. The ultrathin Au film shows optimum electrical conductivity, optical properties, and high tolerance to mechanical bending, including a low sheet resistance of 8 Ω/sq and a high average transmittance of 80.1%, and maintains low electric resistivity even after 1000 continuous bending cycles. Moreover, the Au/AZO anode-based organic light-emitting diode was fabricated with the maximum luminance intensity of 32 540 cd/cm2, which demonstrates that it is promising for application in next generation optoelectronic devices.

Highly Efficient Semitransparent Organic Solar Cells with Color Rendering Index Approaching 100.

Neutral-colored semitransparent organic solar cells (ST-OSCs) have attracted considerable attention owing to their unique application in no-visual-obstacle building-integrated photovoltaics. Toward this promising potential application, a synergistic effect is first proposed by employing a dielectric mirror and ternary photoactive layer with near-infrared absorption to tune the color perception as well as ST-OSC performance precisely. As a result, a neutral-color ST-OSC with high average transmittance of over 21% is successfully constructed, and a remarkable color-rendering index approaching 100 and high power conversion efficiency (PCE) of 9.37% are simultaneously achieved. To the best of our knowledge, this is the highest PCE reported for neutral-color ST-OSCs to date. Importantly, this synergistic effect is demonstrated to be a universal strategy that is not only suitable for various photoactive layer systems, but can also be implanted in flexible substrate. The resulting neutral-color flexible ST-OSCs also show a promising PCE of 8.76%.

Efficient as-cast semi-transparent organic solar cells with efficiency over 9% and a high average visible transmittance of 27.6.

As promising candidates for future applications in building-integrated photovoltaics, semitransparent organic solar cells (ST-OSCs) have made tremendous progress. However, power conversion efficiency (PCE) of the ST-OSCs is limited by intrinsic narrow absorption spectra concentrated in the near infrared region (NIR), weak extinction coefficient, and mismatched molecular energy levels of thin active layers. Here, an efficient ST-OSC based on a donor/acceptor electron pair of a trifluorinated polymer donor PBFTT and a tetrachlorinated acceptor IT-4Cl was fabricated. Due to halogenation, photovoltaic materials show stronger extinction coefficient, improved crystallinity and higher charge carrier mobility; PBFTT shows lower electronic energy levels, and IT-4Cl shows a red-shifted absorption spectrum. As a result, the PBFTT:IT-4Cl pair shows matched energy levels, complementary absorption spectra in the NIR region and a good blend morphology. Hence, as-cast OSCs based on PBFTT:IT-4Cl achieved a high PCE of 11.1% with a high short-circuit current density of 19.7 mA cm-2 and a high fill factor of 73.9%. Owing to the complementary absorption spectra in the NIR region, high EQE values between 600 and 830 nm and a favourable transparency window between 400 and 600 nm, while the human eye has the highest sensitivity in the yellow-green wavelength region (500-600 nm), ST-OSCs using an ultra-thin (10-20 nm) Au cathode showed high PCEs of 7.9-9.1% at a high average visible transmittance of 37.3-27.6% in the photopic region. The PCE of 9.1% is one of the highest values reported in the literature for ST-OSCs without any extra treatment and with an AVT of more than 25% in the photopic region so far.

Room-temperature RF magnetron sputtering deposition of hydrogenated Ga-doped ZnO thin films on PET substrates for PDLC devices

In this work, hydrogenated gallium-doped zinc oxide (HGZO) thin films were deposited on polyethylene terephthalate substrates at room temperature by RF magnetron sputtering. The effects of RF power and Ar + H2 flow rate on electrical and optical properties of HGZO thin films were investigated systematically. All of HGZO thin films exhibited a high average transmittance of about 77.3–82.9% in the visible range, and the minimum resistivity value reached 7.1 × 10− 4 Ω·cm. Potential application of polymer-dispersed liquid crystal device based on HGZO thin film was also successfully demonstrated.

A facile approach to develop modified nano-silica embedded polystyrene based transparent superhydrophobic coating

Triethoxyoctylsilane modified nano-silica (TOS-SiO2) embedded polystyrene (PS) based transparent superhydrophobic coating (SHC) has been synthesized on a glass substrate via a facile sol–gel method. A dip-pulling process was employed to synthesize the coating. The morphology of the PS/TOS-SiO2 coating revealed V-shape dyads like porous structure. The static water contact angle (CA) of 162 ± 2° with a sliding angle (SA) of 3 ± 1° was obtained for the synthesized coating. The thin coating showed a high average transmittance of 91.8 ± 0.5% close to the average transmittance of bare glass (92.6 ± 0.2%). An appropriate amount of TOS-SiO2 embedded PS with unique morphology and average roughness of 65.39 ± 6.7 nm provided a transparent SHC. The transparency and roughness of the SHC were optimized by controlling the dip/pull speed and time. The developed transparent SHC can be utilized for self-cleaning application of the cover glass of solar panels.

Non-ionic surfactant-novel agents to realize high efficiency non-fullerene opaque and semitransparent organic solar cells with Enhanced Stability

The strategy for introducing agents into active layer has been studied as an effective and simple method for optimizing the film morphology and enhancing the performance of organic solar cells (OSCs). Whereas very few agents can be efficient used and make contribution in non-fullerene OSCs. In this work, two novel non-ionic surfactants 1, 8-Octanediol (ODO) and 1, 10-Decanediol (DDO) were introduced to realize high efficiency opaque and semitransparent non-fullerene OSCs for the first time. Doped with an appropriate amount of ODO and DDO in PTB7-Th: ITIC system, highly efficient opaque solar cells have been achieved with a power conversion efficiencies (PCE) of 10.28% and 9.59%, respectively, which exhibited a huge improvement compared with reference cells (PCE of 7.84%). A performance increase is owing to the improvements in short-circuit current density (JSC) and fill factor (FF) via the optimization of the film morphology and the enhanced crystallinity of polymer after adding the surfactant. By using a transparent electrode, the semitransparent OSC shows PCE of 7.74% with high average visible transmittance (AVT) of 21.35%. Moreover, both the stability and efficiency of the OSCs were obviously enhanced by adding the surfactants of ODO and DDO compared with the traditional solvent additives (DIO, CN). Our work clearly expressed that add small amount of non-ionic surfactants could be a simple and efficient strategy to improve the performance of the OSCs.

Transparent bifacial a-Si:H solar cells employing silver oxide embedded transparent rear electrodes for improved transparency

We developed a transparent oxide–metal–oxide (OMO) structure using aluminum-doped zinc oxide and oxidized silver (AgOx) as a transparent electrode of a hydrogenated amorphous silicon (a-Si:H) thin-film solar cell for use in building-integrated photovoltaic (BIPV) windows. The oxygen (O2) addition (O2 flow rate) was optimized for a metal-to-dielectric intermediate-phase AgOx OMO to have high transparency and high conductivity, which were confirmed by finite-difference time-domain simulation. Using the AgOx OMO as a rear electrode, transparent a-Si:H solar cells were fabricated for BIPV window application. The performance of the fabricated cells showed highest bifacial efficiency (b-η) of 7.87% at AgOx OMO of 1 sccm, and highest average transmittance (T500–800, i.e., wavelength range: 500–800 nm) of 21.9% at AgOx OMO of 3 sccm, i.e., improvements from b-η = 7.42% and T500–800 = 18.8% at Ag OMO of 0 sccm. The cell with the optimized AgOx OMO (3 sccm) achieved b-η = 7.69% and the best figure of merit (product of b-η and T500–800) of 169%, i.e., 30% higher than the Ag OMO cell (139%). The developed AgOx OMO electrodes could be used in BIPV windows or in other optical devices requiring both high transparency and high conductivity.

A cracked polymer templated Ag network for flexible transparent electrodes and heaters

In this work, an Ag metal network was fabricated on PET substrate using crackle lithography with acrylic based colloidal dispersion as sacrificial material. The effect of acrylic concentration on optical and electrical properties of Ag electrodes was investigated systematically. All of the Ag electrodes exhibited a high average transmittance of about 74.5%–79.9% in the visible range, and the minimum sheet resistance value reached 8.9 Ω/□. The Ag mesh also showed an excellent mechanical stability for both tensile strain and compressive strain. The fabricated Ag mesh transparent heater exhibited higher heating temperatures (∼95 °C) with lower input voltage (∼6 V), shorter response time (T < 40 s), and lower power consumption (126.9 °C cm2 W−1). Potential application of the Ag mesh based transparent heater in window defogging was also successfully demonstrated.

Improved adhesion of multi-layered front electrodes of transparent a-Si:H solar cells for varying front colors

A low temperature deposition process was developed to fabricate ultra-thin, transparent, multi-layered electrodes (TMEs) suitable to be used on variously shaped flexible substrates, as those utilized in the transparent solar cells of building-integrated photovoltaic (BIPV) systems. The fabricated TMEs consisted of a bottom layer (BL) of gallium doped zinc oxide (GZO), an Ag-layer, and optoelectronic-controlling layers (OCLs) of GZO; and exhibited a high transmittance of 90% at 550 nm, and a low sheet resistance of 9.4 Ω/sq. at the thickness of ~ 100 nm. Because the Ag of TMEs easily detach from inorganic or amorphous surfaces, the GZO-BL was chemically treated in a diluted acetic and nitric acid mixture (10:2) to generate changes in its surface energy and improve the Ag adhesion. To quantitatively evaluate the Ag adhesion of TMEs, we proposed and conducted a tape pull-out adhesion test, and found the optimum GZO-BL texturing condition. The developed TMEs were used as the front transparent conductive electrodes of transparent a-Si:H solar cells to tune their reflection colors. By changing the thickness of the OCL, a wide range of colors was obtained without serious efficiency variations, as was predicted by optical simulations. The fabricated transparent cells show a high efficiency of 4.8%, as well as a high average transmittance of ~ 20% in the visible range. The developed TME structure, using the proposed deposition process, can be fabricated on various substrates and can be applied to devices that require a variety of colors such as BIPVs, wearable PVs, and the PVs of moving vehicles.

A Semitransparent Inorganic Perovskite Film for Overcoming Ultraviolet Light Instability of Organic Solar Cells and Achieving 14.03% Efficiency.

Organic solar cells (OSCs) can be unstable under ultraviolet (UV) irradiation. To address this issue and enhance the power conversion efficiency (PCE), an inorganic-perovskite/organic four-terminal tandem solar cell (TSC) based on a semitransparent inorganic CsPbBr3 perovskite solar cell (pero-SC) as the top cell and an OSC as bottom cell is constructed. The high-quality CsPbBr3 photoactive layer of the planar pero-SC is prepared with a dual-source vacuum coevaporation method, using stoichiometric precursors of CsBr and PbBr2 with a low evaporation rate. The resultant opaque planar pero-SC exhibits an ultrahigh open-circuit voltage of 1.44 V and the highest reported PCE of 7.78% for a CsPbBr3 -based planar pero-SC. Importantly, the devices show no degradation after 120 h UV light illumination. The related semitransparent pero-SC can almost completely filter UV light and well maintain photovoltaic performance; it additionally shows an extremely high average visible transmittance. When it is used to construct a TSC, the top pero-SC acting as a UV filter can utilize UV light for photoelectric conversion, avoiding the instability problem of UV light on the bottom OSC that can meet the industrial standards of UV-light stability for solar cells, and leading to the highest reported PCE of 14.03% for the inorganic-perovskite/organic TSC.

DEPOSITION OF HIGH-ELECTRON-MOBILITY TRANSPARENT CONDUCTING ALUMINUM-DOPED ZINC OXIDE THIN FILMS BY DC MAGNETRON SPUTTERING

Transparent conducting Al-doped ZnO (AZO) thin films were deposited on glass substrates by DC magnetron sputtering from AZO ceramic target (0.75 %wt Al2O3) in gas mixture of (Ar + H2) at different substrate temperatures. At value of 1.7 % of ratio of H2 to (H2+Ar) and at substrate temperature of 200 oC, electron mobility in obtained AZO films is 60.2 cm2.V-1.s-1, which is much larger than 34.6 cm2.V-1.s-1 of films fabricated in the same condition without H2. AZO films also have a low resistivity of 2.53×10-4 Ω.cm, low sheet resistance of 2.5 Ω/□ and high average transmittance above 80 % in the wavelength range of 400 – 1100 nm.

Environmental stability of transparent and conducting ITO thin films coated on flexible FEP and Kapton® substrates for spacecraft applications

Acquiring good adhesion of ITO thin films on polymer substrate is a major concern, especially for space related applications. Delamination of ITO coating on these polymers can seriously damage the spacecraft. This paper presents the development of highly transparent and conducting ITO thin films on as-received and surface treated fluorinated ethylene propylene (FEP) and Kapton® substrates by reactive direct current magnetron sputtering. Stability of the ITO coating on FEP and Kapton® substrates was studied in simulated space environments. Environmental tests such as: relative humidity, thermal cycling and thermo vacuum were performed. Thermo-optical properties and sheet resistance of ITO coated FEP and Kapton® substrates were studied before and after environmental tests. Optimized ITO coating with thickness of ~ 15nm on FEP and Kapton® substrates showed sheet resistance in the range of 2–4kΩ/sq. with high average transmittance and high IR emittance. Adhesion of ITO coating on FEP substrate was improved by Ar plasma etching. X-ray photoelectron spectroscopy and field emission scanning electron microscopic studies of etched FEP substrate showed defluorination and high roughness of the etched surface which helped for better adhesion of ITO coating. We demonstrated that ITO coated plasma etched FEP substrate showed no change in the sheet resistance and thermo-optical properties. Moreover, ITO coated etched FEP substrate showed good environmental stability than ITO coated untreated FEP substrates.

Investigation of the effects of thickness on physical properties of AZO sol-gel films for photonic device applications

Aluminum doped zinc oxide (AZO) films are synthesized on glass substrates using different number of coatings (6, 12, 18 and 24) by the sol-gel dip-coating technique. The effects of thickness on structural, morphological, electrical optical and waveguiding properties of the prepared films are studied through X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), atomic force microscopy (AFM), Hall effect measurements, UV–Visible–NIR spectrophotometer and m-lines spectroscopy (MLS). XRD analysis shows that all AZO films exhibit the hexagonal wurtzite crystal structure with a preferential growth orientation along the c-axis. The intensity of the (002) diffraction peak and crystallite size tend to increase with increase in the thickness indicating an improvement in the crystallinity of the films. Furthermore, the observation of the high-frequency E2 mode in the Raman spectra supports the hexagonal wurtzite structure of ZnO in the films. SEM and AFM images indicate that microstructure parameters, such as grain size and surface roughness depend sensitively on the thickness of the film. The electrical resistivity and carrier concentration are found to increase and decrease, respectively, as the film thickness increased. Optical transmittance spectra demonstrate that all the films exhibit high average transmittance (86.8–89.1%) in the visible spectral range. Moreover, the band gap energy shows a red-shift with the film thickness. MLS measurements at a 632.8 nm wavelength put into evidence that AZO planar waveguides support single and multi-well confined guided modes for both transverse electric (TE) and transverse magnetic (TM) polarizations. Both TE and TM refractive indexes are found to increase with thickness and reach saturation values when the number of coatings is greater than 18. Moreover, the thickest AZO planar waveguide demonstrates a propagation loss lower than 1 dB/cm.

Effect of fluorine and boron co-doping on ZnO thin films: structural, luminescence properties and Hall effect measurements

In this work, undoped and fluorine and boron co-doped ZnO (ZnO:B:F) thin films have been prepared at 400 °C by using Ultrasonic Spray Pyrolysis technique and optical, electrical, structural, surface and luminescence properties of the films have been investigated. Transmission spectra have been taken by UV–VIS spectrophotometer. It is found that ZnO:B:F films have high average optical transmittance. X-ray diffraction (XRD) patterns indicate that the obtained ZnO:B:F has a hexagonal wurtzite type structure with (002) preferential orientation. The crystallite size is calculated by Debye–Scherrer and Williamson–Hall method. Photoluminescence (PL) spectra of the films have been used at room temperature in order to obtain optical properties of the films. Green emission and UV emission band are observed in PL spectra of ZnO and ZnO:B:F. Surface morphologies of the films have been examined using Scanning Electron Microscope (SEM). Compositional analysis has been performed by EDX. The electrical resistivity, carrier concentration and Hall mobility have been measured. The highest Hall mobility of 13.22 cm2 v−1s and the lowest electrical resistivity of 3.13 × 10−4 Ω cm were obtained at the optimal boron-fluorine co-doping concentration of 5 at.%. All of the results have been appreciated in point of view of optoelectronic industry and photovoltaic solar cell applications and it has been concluded that B–F co-doping has a positively effect on electrical properties.

Highly transparent 3D NiO-Ni/Ag-nanowires/FTO micro-supercapacitor electrodes for fully transparent electronic device purpose

In this work, the 3D NiO-Ni/ANWs/FTO electrode for micro-supercapacitor application is fabricated by facile electrochemical deposition and post annealing process. At the optimal under annealing conditions, the composite electrodes demonstrate an excellent specific capacity up to 344 mAh g−1 at 2.5 A g−1 based on GCD result in 2 mol L−1 KOH as electrolyte. In particular, our original welding treatment by rapidly annealing process of the 3D ANWs network dramatically increases the lifetime and stability, ∼100% capacitance retention after 20000 cycles. Meanwhile, the NiO-Ni/ANWs composite own high average transmittance in visible and near infra-red regions as high as 82%, which is suitable for fully transparent electronic device application. For on-chip purpose the FTO substrate has perfect compatibility can also be easily replaced by any shape or form p/n-Si, metal, semiconductor, and any other conductive substrates.

Efficient Semitransparent Organic Solar Cells with Tunable Color enabled by an Ultralow-Bandgap Nonfullerene Acceptor.

Semitransparent organic solar cells (OSCs) show attractive potential in power-generating windows. However, the development of semitransparent OSCs is lagging behind opaque OSCs. Here, an ultralow-bandgap nonfullerene acceptor, "IEICO-4Cl", is designed and synthesized, whose absorption spectrum is mainly located in the near-infrared region. When IEICO-4Cl is blended with different polymer donors (J52, PBDB-T, and PTB7-Th), the colors of the blend films can be tuned from purple to blue to cyan, respectively. Traditional OSCs with a nontransparent Al electrode fabricated by J52:IEICO-4Cl, PBDB-T:IEICO-4Cl, and PTB7-Th:IEICO-4Cl yield power conversion efficiencies (PCE) of 9.65 ± 0.33%, 9.43 ± 0.13%, and 10.0 ± 0.2%, respectively. By using 15 nm Au as the electrode, semitransparent OSCs based on these three blends also show PCEs of 6.37%, 6.24%, and 6.97% with high average visible transmittance (AVT) of 35.1%, 35.7%, and 33.5%, respectively. Furthermore, via changing the thickness of Au in the OSCs, the relationship between the transmittance and efficiency is studied in detail, and an impressive PCE of 8.38% with an AVT of 25.7% is obtained, which is an outstanding value in the semitransparent OSCs.