Average Visible Transmittance Research Articles

High conductivity and transparent aluminum-based multi-layer source/drain electrodes for thin film transistors

In this study, high conductivity and transparent multi-layer (AZO/Al/AZO-/Al/AZO) source/drain (S/D) electrodes for thin film transistors were fabricated via conventional physical vapor deposition approaches, without toxic elements or further thermal annealing process. The 68 nm-thick multi-layer films with excellent optical properties (transparency: 82.64%), good electrical properties (resistivity: 6.64 × 10−5 Ω m, work function: 3.95 eV), and superior surface roughness (Rq = 0.757 nm with scanning area of 5 × 5 µm2) were fabricated as the S/D electrodes. Significantly, comprehensive performances of AZO films are enhanced by the insertion of ultra-thin Al layers. The optimal transparent TFT with this multi-layer S/D electrodes exhibited a decent electrical performance with a saturation mobility (µsat) of 3.2 cm2 V−1 s−1, an Ion/Ioff ratio of 1.59 × 106, a subthreshold swing of 1.05 V/decade. The contact resistance of AZO/Al/AZO/Al/AZO multi-layer electrodes is as low as 0.29 MΩ. Moreover, the average visible light transmittance of the unpatterned multi-layers constituting a whole transparent TFT could reach 72.5%. The high conductivity and transparent multi-layer S/D electrodes for transparent TFTs possessed great potential for the applications of the green and transparent displays industry.

Fused Tris(thienothiophene)-Based Electron Acceptor with Strong Near-Infrared Absorption for High-Performance As-Cast Solar Cells.

A fused tris(thienothiophene) (3TT) building block is designed and synthesized with strong electron-donating and molecular packing properties, where three thienothiophene units are condensed with two cyclopentadienyl rings. Based on 3TT, a fused octacylic electron acceptor (FOIC) is designed and synthesized, using strong electron-withdrawing 2-(5/6-fluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)-malononitrile as end groups. FOIC exhibits absorption in 600-950 nm region peaked at 836 nm with extinction coefficient of up to 2 × 105 m-1 cm-1 , low bandgap of 1.32 eV, and high electron mobility of 1.2 × 10-3 cm2 V-1 s-1 . Compared with its counterpart ITIC3 based on indacenothienothiophene core, FOIC exhibits significantly upshifted highest occupied molecular orbital level, slightly downshifted lowest unoccupied molecular orbital level, significantly redshifted absorption, and higher mobility. The as-cast organic solar cells (OSCs) based on blends of PTB7-Th donor and FOIC acceptor without additional treatments exhibit power conversion efficiencies (PCEs) as high as 12.0%, which is much higher than that of PTB7-Th: ITIC3 (8.09%). The as-cast semitransparent OSCs based on the same blends show PCEs of up to 10.3% with an average visible transmittance of 37.4%.

Simultaneously improved efficiency and average visible transmittance of semitransparent polymer solar cells with two ultra-narrow bandgap nonfullerene acceptors

The efficiency and average visible transmittance of semitransparent polymer solar cells can be simultaneously improved by employing a ternary strategy.

Structure and optoelectrical properties of transparent conductive MGZO films deposited by magnetron sputtering

The transparent conductive Mg-Ga co-doped ZnO (MGZO) films were prepared by radio-frequency (RF) magnetron sputtering. The influence of substrate temperature on the structural and optoelectrical properties of the films is studied. The results show that all the films possess a preferential orientation along the (002) plane. With the increase of substrate temperature, the structure and optoelectrical properties of the films can be changed. When substrate temperature is 300 °C, the deposited film exhibits the best crystalline quality and optoelectrical properties, with the minimum micro strain of 1.09×10-3, the highest average visible transmittance of 82.42%, the lowest resistivity of 1.62×10-3 Ω·cm and the highest figure of merit of 3.18×103 Ω-1·cm-1. The optical bandgaps of the films are observed to be in the range of 3.342—3.545 eV. The refractive index dispersion curves obey the Sellmeier’s dispersion model.

Breaking 10% Efficiency in Semitransparent Solar Cells with Fused-Undecacyclic Electron Acceptor

A fused-undecacyclic electron acceptor IUIC has been designed, synthesized and applied in organic solar cells (OSCs) and semitransparent organic solar cells (ST-OSCs). In comparison with its counterpart, fused-heptacyclic ITIC4, IUIC with a larger π-conjugation and a stronger electron-donating core exhibits a higher LUMO level (IUIC: −3. 87 eV vs ITIC4: −3.97 eV), 82 nm red-shifted absorption with larger extinction coefficient and smaller optical bandgap, and higher electron mobility. Thus, IUIC-based OSCs show higher values in open-circuit voltage, short-circuit current density, and thereby much higher power conversion efficiency (PCE) than those of the ITIC4-based counterpart. The as-cast OSCs based on PTB7-Th: IUIC without any extra treatment yield PCEs of up to 11.2%, higher than that of the control devices based on PTB7-Th: ITIC4 (8.18%). The as-cast ST-OSCs based on PTB7-Th: IUIC without any extra treatment afford PCEs of up to 10.2% with an average visible transmittance (AVT) of 31%, higher than th...

Structural, optical and electrical characterization of Ga-Mg co-doped ZnO transparent conductive films

The transparent conducting Ga-Mg co-doped ZnO films were prepared on glass substrates by radio-frequency (rf) magnetron sputtering. The effect of growth temperature on structural, morphological and optoelectronic properties of the films was investigated by XRD, XPS, SEM, UV-visible spectrophotometer and four-point probe. The results show that all the films are polycrystalline and (0 0 2) oriented. The growth temperature significantly affects the structure and optoelectronic properties of the films. The film deposited at the growth temperature of 270 °C has the largest grain size of 52.38 nm, the minimum tensile stress of 0.037GPa, the highest average visible transmittance of 89.39%, the lowest resistivity of 1.52 × 10−3 Ω⋅cm and the maximum figure of merit of 5.87 × 103 Ω-1⋅cm-1. Furthermore, the optical bandgaps were determined by extrapolation method and observed to be in the range of 3.36–3.59 eV.

Dual Function of UV/Ozone Plasma-Treated Polymer in Polymer/Metal Hybrid Electrodes and Semitransparent Polymer Solar Cells.

In this work, high-performance inverted indium tin oxide (ITO)-free semitransparent polymer solar cells are comprehensively investigated using a novel polymer/metal hybrid transparent electrode. The electrical and optical characteristics of hybrid electrodes are significantly enhanced by introducing UV/ozone plasma treatment on the polymer poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN), which is functioned as both a seed layer for ultrathin Ag metal electrode and an optical spacer for transparent devices. The optimized sheet resistance of PFN/Ag (12 nm) hybrid electrode is only half of the commercial ITO (9.4 vs 20.0 Ω sq-1) and the high wavelength-dependent reflectance of hybrid electrode helps to increase the ITO-free device short-circuit current density. Furthermore, the interface property between PFN and ultrathin Ag is analyzed in detail and the optical field distribution is calculated for comparison. A high power conversion efficiency of 5.02%, which is increased by 35% compared to that of the ITO-based device, is achieved in the ITO-free semitransparent device in conjunction with an excellent average visible transmittance above 28% that is higher than the benchmark of 25% for power-generating window, indicating its great potential in building integrated photovoltaic systems in the future. Furthermore, the strategy is successfully developed for other polymer systems, suggesting the universal applicability for plastic electronics.

Work function optimization of vacuum free top-electrode by PEDOT:PSS/PEI interaction for efficient semi-transparent perovskite solar cells

Our research group fabricated low temperature based inverted semi-transparent CH3NH3PbI3 perovskite photovoltaics. The work function of PEDOT:PSS (PH1000) electrode was modified using polyethylenimine (PEI) and both layers are transferred on the ITO/PEDOT:PSS/CH3NH3PbI3/PCBM layer using hydrophobic polyurethane acrylate (PUA) polymer stamp. Even if the PH1000 spin coating on the CH3NH3PbI3/PCBM layer shows degradation of perovskite due to the inter-diffusion of PH1000 solvent, drying transfer shows effective layer stacking without degradation. The PEI treatment on the PH1000 contributes to reduce the work function from 5.1eV to 3.97eV and this modification makes to improve the device performance from 0.07% to 4.02%. The full device average visible transmittance (AVT) exhibits 24.53% and the work function modification shows the decreased charge transporting resistance (Rc), which directly correlate to the enhanced open circuit voltage (Voc) short circuit current (Jsc) and fill factor (FF).

Flexible and Semitransparent Organic Solar Cells

AbstractFlexible and semitransparent organic solar cells (OSCs) have been regarded as the most promising photovoltaic devices for the application of OSCs in wearable energy resources and building‐integrated photovoltaics. Therefore, the flexible and semitransparent OSCs have developed rapidly in recent years through the synergistic efforts in developing novel flexible bottom or top transparent electrodes, designing and synthesizing high performance photoactive layer and low temperature processed electrode buffer layer materials, and device architecture engineering. To date, the highest power conversion efficiencies have reached over 10% of the flexible OSCs and 7.7% with average visible transmittance of 37% for the semitransparent OSCs. Here, a comprehensive overview of recent research progresses and perspectives on the related materials and devices of the flexible and semitransparent OSCs is provided.

High Efficiency Near-Infrared and Semitransparent Non-Fullerene Acceptor Organic Photovoltaic Cells.

The absence of near-infrared (NIR) solar cells with high open circuit voltage (Voc) and external quantum efficiency (EQE) has impeded progress toward achieving organic photovoltaic (OPV) power conversion efficiency PCE > 15%. Here we report a small energy gap (1.3 eV), chlorinated nonfullerene acceptor-based solar cell with PCE = 11.2 ± 0.4%, short circuit current of 22.5 ± 0.6 mA cm-2, Voc = 0.70 ± 0.01 V and fill factor of 0.71 ± 0.02, which is the highest performance reported to date for NIR single junction OPVs. Importantly, the EQE of this NIR solar cell reaches 75%, between 650 and 850 nm while leaving a transparency window between 400 and 600 nm. The semitransparent OPV using an ultrathin (10 nm) Ag cathode shows PCE = 7.1 ± 0.1%, with an average visible transmittance of 43 ± 2%, Commission d'Eclairage chromaticity coordinates of (0.29, 0.32) and a color rendering index of 91 for simulated AM1.5 illumination transmitted through the cell.

Microstructure and optoelectronic properties of gallium–magnesium codoped zinc oxide thin films by magnetron sputtering technique

The gallium–magnesium codoped zinc oxide (GMZO) thin films were deposited on glass substrates by radio frequency magnetron sputtering technique in an argon atmosphere. The influence of substrate temperature on the microstructure, morphology and optoelectronic properties of thin films was investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, four-point probe and spectrophotometry. It is found that all the deposited films have a hexagonal structure and a preferred orientation along the c-axis perpendicular to the substrate. As the substrate temperature increases, the dislocation density, lattice strain and electrical resistivity decrease initially and then increase, while the average crystallite size, average visible transmittance and figure of merit exhibit the reverse variation trend. The GMZO thin film deposited at the substrate temperature of 570 K possesses the best optoelectronic properties, with the largest average crystallite size of 52.05 nm, the lowest dislocation density of 3.69 × 1014 lines m− 2, the minimum lattice strain of 1.10 × 10− 3, the lowest electrical resistivity of 1.62 × 10− 3 Ω cm, the highest average visible transmittance of 88.63% and the maximum figure of merit of 5.11 × 103 Ω−1 cm− 1. The optical energy gaps of the films were evaluated by extrapolation method and observed to be in the range of 3.34–3.55 eV. Furthermore, the complex refractive index, the complex dielectric constant and the dissipation factor were determined by optical characterization methods, and the dispersion behaviour of refractive index was studied in terms of the single electronic oscillator model. The results show that the microstructure and optoelectronic properties of the GMZO thin films are dependent on substrate temperature.

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.

Development of Sol Gel Derived Nanocrystalline TiO2 Thin Films via Indigenous Spin Coating Method

In this paper, indigenous spin coater apparatus was fabricated and characterized by depositing transparent semiconducting thin films of TiO2 on glass substrates for 90 s at 6000 rpm followed by calcination procedures. The influence of the calcination temperature (400–800 °C) on electrical, optical, structural and photocatalytic properties of nano-crystalline titanium dioxide (TiO2) thin film were studied by four point probes, absorbance spectrum, X-ray diffraction (XRD), and photocatalytic activity test respectively. It has been investigated that the effect of conductivity increase may be caused by the increase of temperature. The XRD results showed that TiO2 thin film calcined at 400 °C was anatase, and further transformed into the rutile phase at higher calcination temperature. The crystallite size of TiO2 thin films was increased with increasing calcination temperature. Experimental results depicts that structural and electrical properties of the films are highly dependent on the growth temperature. It was observed that with increasing growth temperature, the average visible transmittance of the deposited films is enhanced and the residual stress in the thin films is obviously relaxed. The optical band gap energy decreases with increasing calcination temperature upto certain limit. Photocatalytic activity of thin films, evaluated by disintegration of methyl blue, methyl orange and RhB, was increased with variation in calcination temperature for a particular range. At 700 °C, the TiO2 thin film showed the highest photocatalytic activity due to better crystallization of TiO2 in the composite thin film.

High-Efficiency Semitransparent Organic Solar Cells with Non-Fullerene Acceptor for Window Application

Organic solar cells possess multiple desirable traits, such as low cost, flexibility, and semitransparency, which opens up potential avenues unavailable to other solar technologies, a prime example of this being window applications. For this specific application, a delicate balance between the transmission of light through the device and power conversion efficiency (PCE), dependent on the amount of light absorbed, must be optimized. Here, we report a high-efficiency semitransparent device based on a novel fullerene-free material system. Using an active layer based on the material system PBDB-T:ITIC, optimized devices exhibited PCEs exceeding 7% while also achieving an average visible transmittance (AVT) of 25%. The concurrent demonstration of high efficiency with an AVT of 25% represents a notable step forward for semitransparent organic solar cells. Additionally, the influence of the active layer thickness on the color rendering properties of these cells was studied. Optimization of the active layer thic...

Room-temperature UV-ozone assisted solution process for zirconium oxide films with high dielectric properties

Abstract A facile, low-cost, and room-temperature UV-ozone (UVO) assisted solution process was employed to prepare zirconium oxide (ZrO x ) films with high dielectric properties. ZrO x films were deposited by a simple spin-coating of zirconium acetylacetonate (ZrAcAc) precursor in the environment-friendly solvent of ethanol. The smooth and amorphous ZrO x films by UVO exhibit average visible transmittances over 90% and energy bandgap of 5.7 eV. Low leakage current of 6.0 × 10 −8 A/cm 2 at 3 MV/cm and high dielectric constant of 13 (100 Hz) were achieved for ZrO x dielectrics at the nearly room temperature. Moreover, a fully room-temperature solution-processed oxide thin films transistor (TFT) with UVO assisted ZrO x dielectric films achieved acceptable performances, such as a low operating voltage of 3 V, high carrier mobility of 1.65 cm 2 V −1 s −1 , and on/off current ratio about 10 4 –10 5 . Our work indicates that simple room-temperature UVO is highly potential for low-temperature, solution-processed and high-performance oxide films and devices.

Highly stable semi-transparent CH3NH3PbI3 sandwich type perovskite solar sub-module with neutral color

∼10% semi-transparent neutral color sandwich type CH3NH3PbI3 (MAPbI3) perovskite sub-module (active area = 25 cm2) with UV cross-linked polystyrene passivation layer showed ∼2.8% degradation of initial efficiency after continuous light soaking of 1 Sun for 1000 h at 55 °C. Due to the role of island-morphology-MAPbI3 as selective UV-cut mask, the UV curable monomeric compounds on the island-morphology-MAPbI3/blocking TiO2/F-doped tin oxide substrate could be selectively cross-linked polymerized by exposure of UV light and consequently the UV cured passivation layer could be reproducibly deposited in the gaps between perovskite islands after simple washing of unreacted residue. The degree of cross-linking was controlled by adjusting the concentration of divinylbezene cross-linker in the UV curable monomeric compounds from 1 to 7 mol% and eventually 5 mol% sample showed the best power conversion efficiency of 11.58% for forward scan condition and 11.95% for reverse scan condition (active area = 1 cm2, geometric fill factor = 100%, average = 10.28 ± 0.96% for 40 samples: average visible transmittance = 20.1%). When the active area of the MAPbI3 perovskite sub-module increases to 1 → 25 → 100 cm2, the power conversion efficiency was slightly decreased to 11.95 → 10.16 → 7.08% at 1 Sun condition.

Synergic Interface and Optical Engineering for High‐Performance Semitransparent Polymer Solar Cells

AbstractIn this study the thickness of the PTB7‐Th:PC71BM bulk heterojunction (BHJ) film and the PF3N‐2TNDI electron transport layer (ETL) is systematically tuned to achieve polymer solar cells (PSCs) with optimized power conversion efficiency (PCE) of over 9% when an ultrathin BHJ of 50 nm is used. Optical modeling suggests that the high PCE is attributed to the optical spacer effect from the ETL, which not only maximizes the optical field within the BHJ film but also facilitates the formation of a more homogeneously distributed charge generation profile across the BHJ film. Experimentally it is further proved that the extra photocurrent produced at the PTB7‐Th/PF3N‐2TNDI interface also contributes to the improved performance. Taking advantage of this high performance thin film device structure, one step further is taken to fabricate semitransparent PSCs (ST‐PSCs) by using an ultrathin transparent Ag cathode to replace the thick Ag mirror cathode, yielding a series of high performance ST‐PSCs with PCEs over 6% and average visible transmittance between 20% and 30%. These ST‐PSCs also possess remarkable transparency color perception and rendering properties, which are state‐of‐the‐art and fulfill the performance criteria for potential use as power‐generating windows in near future.

Low temperature deposition of highly transparent and conducting Al-doped ZnO films by RF magnetron sputtering

Radio frequency (rf) magnetron sputtering process was optimized to deposit highly conducting and transparent polycrystalline Al-doped ZnO (ZnO:Al or AZO) films at low temperature. Deposition was done in pure argon atmosphere on unheated glass substrates. Various properties of AZO films, such as residual stress, crystallite size, Al content, carrier concentration and mobility, resistivity, optical transmittance, band-gap and refractive index were measured and their variation with deposition power and working pressure was analyzed. In the first step deposition power was varied from 200 W to 1200 W at a constant working pressure, and then in the next step working pressure was varied from 0.05 to 0.5 Pa while keeping deposition power constant at the optimized value. Film thickness was maintained constant at 600 ± 50 nm. Obtained results were compared with those of other researchers wherever possible. With increasing deposition power it was observed that film properties improve up to a certain power and then start to deteriorate with further increase of power. Electrical properties were found to depend more strongly on structural properties of films, compared to optical properties. At optimized deposition power film properties showed a weaker dependence on working pressure in the used range. Best quality AZO films with 6.7 × 10−4 Ω-cm electrical resistivity and 90% average visible transmittance were obtained at 600 W deposition power and 0.1 Pa working pressure.

Structural, Electrical and Optical Properties of Ternary Al<sub>2</sub><i><sub>x</sub></i>In<sub>2(1-</sub><sub>x</sub><sub>)</sub>O<sub>3</sub> Films Prepared by Metal Organic Chemical Vapor Deposition

New wide band gap semiconductors with tunable properties are desperately needed to meet the ever-increasing demands of photoelectric devices operating in the ultraviolet (UV) or even deep ultraviolet (DUV) region. In this study, the ternary aluminum indium oxide (Al2xIn2(1-x)O3) films with different Al compositions of x [Al/(Al+In) atomic ratio] were successfully grown on the α-Al2O3 (0001) substrates at 650 °C by metal organic chemical vapor deposition (MOCVD). The influence of Al content on the structural, compositional, electrical and optical properties of the obtained films was investigated in detail. The structural transition from polycrystalline structure of bixbyite In2O3 to amorphous was observed as the Al content increased. The lowest resistivity of 1.52×10-3 Ω·cm was obtained for the sample with x=0.2, along with the respective hall mobility and carrier concentration values of 12.87 cm2V-1s-1 and 2.27×1020 cm-3. The average visible transmittances of over 83% were demonstrated for all the samples. The calculated values of optical band gap for the films indicated continuous increase from 3.82 to 5.88 eV as the x value increased from 0.1 to 0.9. The Al2xIn2(1-x)O3 films with tunable properties may be potentially employed in the fabrication of transparent optoelectronic devices, such as UV detectors, transparent TFTs and short wavelength light-emitting devices.

Low temperature synthesis of ZnO nanowires on GAZO thin films annealed at different temperatures for solar cell application

ZnO nanowires were hydrothermally grown on sputtered gallium and aluminium co-doped ZnO (GAZO) thin films as seed layers and the effect of seed layer annealing temperature on their microstructural and optoelectronic properties was investigated. Atomic force microscopy revealed an increase in the GAZO films' mean particle size and surface roughness with annealing temperature. The GAZO films exhibited a zincite phase with a preferred orientation along the (002) plane and their crystallinity improved with annealing temperature, resulting in low electrical resistivity. The nanowires' alignment improved with seed layer annealing temperature up to 150°C and then deteriorated at 250−350°C. This was attributed to the improvement in nanowire crystallinity up to 150°C and its deterioration at 250–350°C. Energy dispersive spectroscopy confirmed that the nanowires were closer to stoichiometric ZnO (1:1). Raman spectroscopy revealed the presence of few defects and slight residual tensile stress in the nanowires, in corroboration with XRD analysis. The films and nanowires exhibited average visible transmittances around 75–85% and 50–80%, respectively. The least electrical resistivity (7.0×10−3Ωcm) and highest figure of merit (1.02×10−2Ω−1) were obtained for the well-aligned nanowires grown on 150°C annealed films, demonstrating their suitability for solar cell transparent electrode fabrication.