Photovoltaic property dependence of dye-sensitized solar cells on sheet resistance of FTO substrate deposited via spray pyrolysis

F-doped SnO₂ (FTO) glass substrate was successfully fabricated via spray-pyrolysis deposition for use as a transparent conducting substrate in dye-sensitized solar cells (DSSCs). To investigate the performance dependence of DSSCs on the sheet resistance of the FTO films, three types of FTO films with sheet resistance values of 2 Ω/□, 4 Ω/□, and 10 Ω/□ were fabricated. Commercial FTO films having a sheet resistance of 15 Ω/□ were prepared for comparison. The structural, electrical, and optical properties of FTO films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), the four-point probe method, and UV–vis spectrometry. The photocurrent–voltage data show that DSSCs fabricated with a sheet resistance of 2 Ω/□ exhibit the best photoconversion effciency (～5.5%) among the four samples. The performance improvement of DSSCs is due to improved short-circuit current density (～13.7 mA/cm²) and fill factor (～62.3%).     

Optoelectronic multifunctionality of combustion-activated fluorine-doped tin oxide films with high optical transparency

As transparent conducting oxides (TCOs) have been widely used as a common component of many optoelectronic applications, ensuring high conductivity and transparency TCOs has become a pivotal concern. In the present study, we report developing the combustion-activated pyrolysis route of horizontal ultrasonic spray pyrolysis deposition (HUSPD) as a novel strategy to form highly transparent conducting fluorine-doped tin oxide (FTO) films. Compared to the basic route, the combustion-activated FTO films showed an attractive transparent conducting performance (figure of merit of 5.34?×?10^?2?Ω^?1) with a highly improved optical transparency (90.1%) due to the formation of a smooth and dense film structure to reduce light scattering on the surface, and a decrease of oxygen vacancies to broaden the optical bandgap, all of which yielded an excellent performance as compared to the previously reported studies on the FTO films. Moreover, when the combustion-activated FTO films were used as TCOs of electrochromic devices and dye-sensitized solar cells, they acquired multifunctional effects of (a) an efficient electron transfer by (200) preferred orientations of the FTO; (b) a relaxed light scattering on the interface due to smooth and dense surface morphology of the FTO films; and (c) a broad optical bandgap by decreased oxygen vacancies, resulting in an impressive improvement of both electrochromic and photovoltaic performances. Taken together, our results demonstrate that combustion-activated FTO films are an attractive technique for forming high-performance TCOs that can further be used in multifunctional optoelectronic devices.     

The sheet resistance of graphene under contact and its effect on the derived specific contact resistivity

It is normally assumed that the sheet resistances under and outside the metal contact are identical when deriving specific contact resistivity of graphene from transmission line model. We considered the contact end resistance and obtained the sheet resistance under contact of 670 Ω/□, which is much different from that outside the contact of 1840 Ω/□. Considering the difference, the value of specific contact resistivity is determined to be 3.3 × 10⁻⁶ Ω cm², which is three times as large as the unmodified value. This indicates that the difference between the sheet resistances under and outside the contact affects the derived specific contact resistivity of graphene significantly.     

Essential Macleod Program (EMP) simulated fabrication of high quality Zn:SnO2/Ag/Zn:SnO2 multilayer transparent conducting electrode on flexible substrates

In the quest of promising Indium free amorphous transparent conducting oxide (TCO), Zn-doped SnO₂/Ag/Zn-doped SnO₂ (OMO) multilayer films were prepared on flexible polyethylene terephthalate (PET) substrates by RF sputtering at room temperature (RT). Growth parameters were optimized by varying sputtering power and working pressure, to have high electrical conductivity and optical transmittance. Optimization of the thickness of each layer was done by Essential Macleod Program (EMP) simulation to get the higher transmission through OMO multilayer. The sheet resistance and transmittance of 3 at% Zn-doped SnO₂ thin film (30 nm) were 2.23 kΩ/□, (ρ ~ 8.92×10⁻³ Ω∙cm) and 81.3% (at λ ~ 550 nm), respectively. By using optimized thicknesses of Zn-doped SnO₂ (30 nm) and Ag (12 nm) and optimized growth condition Zn-doped SnO₂/Ag/Zn-doped SnO₂ multilayer thin films were deposited. The low sheet resistance of 7.2 Ω/□ and high optical transmittance of 85.1% in the 550 nm wavelength region was achieved with 72 nm multilayer film.     

Growth control of RF magnetron sputtered SrRuO3 thin films through the thickness of LaNiO3 seed layers

SrRuO₃ (SRO) thin films were grown on SiO₂/Si substrates with different thickness of LaNiO₃ (LNO) seed layers by RF magnetron sputtering. Effects of LNO thickness on the grain orientation, surface morphology, magnetic behavior and electrical transport properties of SRO films were investigated. The orientation of SRO films transformed from (110)_pc to (001)_pc and the residual stress was released gradually with increasing the thickness (pc refers to the pseudo-cubic unit cell of SrRuO₃). SRO films with higher orientation grown on LNO exhibited more flat surface, higher saturation magnetization, and lower coercive field. The magnetic anisotropy was enhanced on thicker LNO due to the different states of residual stress. In addition, the temperature dependence of resistivity was promoted by the microstructural disorder. (110)_pc-oriented SRO monolayer electrode and (001)_pc-oriented SRO/LNO300 bilayer electrode own low room temperature sheet resistance of 0.38 Ω/□ and 0.26 Ω/□, respectively. The results indicate that the controllable SRO films can be used as not only good bottom electrodes but also promising templates to control the crystallographic orientations of various other perovskite-based functional materials.     

Effects of Sb-doped SnO2–WO3 nanocomposite on electrochromic performance

With the increase in global challenges related to energy depletion, there is significant emphasis on studies involving next-generation optoelectronic applications such as smart windows and electronic displays. In particular, electrochromic devices (ECDs) have been identified as strategic innovations for energy-saving “smart windows” to address these challenges. Despite this increased level of attentions, ECDs have not yet attained broad commercial acceptance because of their limited electrochromic (EC) properties including coloration efficiency (CE,< 30.0 cm²/C) and switching speeds (> 10.0 s). To address these limitations, critical effort is required to enhance the EC properties by tuning the film structure and electronic structure of ECDs. In this study, we demonstrated the effect of nanocomposite structure of conductive metal oxides and WO₃ EC films. Antimony-doped tin oxide nanoparticles (ATO NPs) were utilized because of their superior electrical conductivity and large band gap. To achieve the optimum addition amount of ATO NPs in EC films, we adjusted the amount as 0, 0.6, 1.2, 2.4 wt%. WO₃ EC films with the optimum addition amount (1.2 wt%) of ATO NPs exhibited improved EC performance including both the switching speeds (5.4 s for the coloration speed and 2.4 s for the bleaching speed) and CE value (48.2 cm²/C). The enhancement of EC performance was attributed to the well-dispersed ATO NPs in the WO₃ films that can effectively improve electrical conductivity via the formation of by forming preferred electron pathway. In addition, the large band gap of ATO NPs broadens the transmittance modulation of the EC layer which contributed to the increment of the CE value. Therefore, our results suggest a strategy to obtain the enhanced WO₃ films with superior EC performances using conductive metal oxides nanocomposite structure.     

Oxygen Distribution of Fluorine-doped Tin Oxide Films Coated on Float Glass along Depth Before and After Heat Treatment

Fluorine-doped tin oxide (FTO) films were deposited on float glass to create low-emissivity glass (low-E glass) by atmospheric pressure chemical vapor deposition (APCVD). Heat treatments were carried out to assess its antioxidant properties. The surface morphology, crystal structure, and the oxygen and tin concentrations in the FTO films were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), Auger electron spectrometer (AES), and X-ray photoelectron spectroscopy (XPS), respectively. The results indicated that the electrical properties determined by the four-point probe method remained constant up to 600°C with increasing temperature. The FTO films exhibited nonstoichiometry with a ratio of [O]/[Sn] >2 on the top surface and <2 in the film. The sheet resistance of the film strongly depended on the oxygen concentration on the film surface. When the heating temperature reached 700°C, the sheet resistance increased rapidly from 9.4 to 86.7 Ω/□ with a concomitant increase in the oxygen concentration on the top surface.     

Simple and rapid synthesis of NiO/PPy thin films with improved electrochromic performance

Nickel oxide/polypyrrole (NiO/PPy) thin films were deposited by a two step process in which the NiO layer was electrodeposited potentiostatically from an aqueous solution of NiCl₂·6H₂O at pH 7.5 on fluorine doped tin oxide (FTO) coated conducting glass substrates, followed by the deposition of polypyrrole (PPy) thin films by chemical bath deposition (CBD) from pyrrole mixed with ammonium persulfate (APS). The NiO/PPy films were further characterized for their structural, optical, morphological and electrochromic properties. X-ray diffraction study indicates that the films composed of polycrystalline NiO and amorphous PPy. Infrared transmission spectrum reveals chemical bonding between NiO and PPy. Rectangular faceted grains were observed from scanning electron microscopy results. The electrochromic (EC) property of the film was studied using cyclic voltammogram (CV), chronoamperometry (CA) and optical modulation. The NiO/PPy presents superior EC properties than their individual counterparts. The coloration/bleaching kinetics (response time of few ms) and coloration efficiency (358 cm²/C) were found to be improved appreciably. The dramatic improvement in electrochemical stability (from about 500 c/b cycles for PPy to 10,000 c/b cycles for NiO/PPy) was observed. This work therefore demonstrates a cost-effective and simple way of depositing highly efficient, faster and stable NiO/PPy electrodes for EC devices.     

Fe doping effect of vanadium oxide films for enhanced switching electrochromic performances

In the present study, Fe-doped V₂O₅ films showing impressive electrochromic (EC) performance were developed using the sol-gel spin-coating method. To confirm the optimized Fe-doping effect on the V₂O₅ films for the EC performance, we adjusted the Fe atomic percentages to 0.0, 0.5, 1.0, and 1.5?at%, respectively. With the effect of Fe doping on the V₂O₅ films, the obtained films resulted in the formation of the oxygen vacancies. As the result, when the optimum Fe atomic percentage was 1.0?at%, the enhanced switching speeds (3.7?s for the bleaching speed and 2.0?s for the coloration speed) and enhanced coloration efficiency value (47.3?cm²/C) compared to the other films were implemented. This can be attributed to the improved electrical conductivity and Li⁺ diffusion coefficient that led to efficient generation of the EC reaction activity and narrowing the optical bandgap at the coloration state to increase transmittance modulation. Therefore, this unique film can be a promising EC material to improve the performance for the EC devices.     

Ultrasonic-vibration-assisted laser annealing of fluorine-doped tin oxide thin films for improving optical and electrical properties: Overlapping rate optimization

An ultrasonic-vibration-assisted laser annealing method was developed to enhance the performance of fluorine-doped tin oxide (FTO) thin films. The influences of ultrasonic vibration, laser scan line overlapping rate (L_OR) and laser spot overlapping rate (S_OR) on surface morphology, FTO layer thickness, RMS roughness, crystal structure and photoelectric properties of the FTO films were investigated. The results indicated that the presence of ultrasonic vibration during laser annealing could significantly enhance the film compactness, and using moderate L_OR and S_OR values resulted in significantly decreased FTO layer thicknesses and RMS roughnesses as well as slightly increased crystallite sizes, thus yielding significantly improved optical transmittance values and slightly enhanced electrical conductivity values. It was found that the optimal L_OR and S_OR values for ultrasonic-vibration-assisted laser annealing of the FTO films were 80% and 90%, respectively. The as-obtained film possessed the best overall photoelectric property with an average transmittance (400–800?nm) of 85.9%, a sheet resistance of 8.7?Ω/sq and a figure of merit of 2.51?×?10^–2 Ω^–1. This work may be of great significance in terms of performance optimization of transparent conducting oxide (TCO) thin films.     

Growth control of single-walled, double-walled, and triple-walled carbon nanotube forests by a priori electrical resistance measurement of catalyst films

We present the wall number control of carbon nanotube (CNT) forests grown on metal catalyst films in a water-assisted chemical vapor deposition (CVD) by measuring the sheet resistances of metal catalyst films. Catalyst film thicknesses and thickness variations are monitored using a 2-point-based electrical characterization methodology. The electrical characterization and high-resolution transmission electron microscopy analysis showed that single-, double-, and triple-walled CNT forests were grown on iron (Fe) catalyst films with mean sheet resistances of 646.63, 75.40, and 27.84 MΩ/sq, respectively. The average wall number and outer diameter of CNT forests were found to linearly depend on the logarithm of the mean sheet resistances of Fe catalyst films.     

Thermally stable and transparent F-doped SnO2 (FTO) /Ag/FTO films for transparent thin film heaters used in automobiles

We investigated the characteristics of F-doped SnO₂ (FTO)/Ag/FTO films prepared using thermal evaporation at room temperature for the application of the as-formed films in transparent thin film heaters (TFHs) of automobiles. To optimize the electrical and optical properties of the FTO/Ag/FTO multi-layer, the figure of merit (FoM) values of the FTO/Ag/FTO multi-layers were compared as a function of the thickness of the Ag and FTO layers. The sheet resistance and optical transmittance of the FTO/Ag/FTO multi-layer were primarily affected by the Ag inter-layer and bottom/top FTO thicknesses, respectively. At optimized Ag (10 nm) and FTO (40 nm) thicknesses, we fabricated a FTO/Ag/FTO electrode with a sheet resistance of 8.00 Ohm/square, an optical transmittance of 83.04 % at a visible wavelength (400–800 nm) and a FoM value of 19.49 Ohm^-1. The TFHs comprising the optimal FTO/Ag/FTO electrode exhibited a saturated temperature of 117 °C at a low operating direct current of 6 V, owing to the low sheet resistance. In addition, the FTO/Ag/FTO-based TFHs exhibited thermally stable performances owing to the stability of the bottom and top FTO electrodes. The performance of the FTO/Ag/FTO-based TFHs demonstrated that the thermally evaporated FTO/Ag/FTO multi-layer is a promising, stable, and transparent electrode material for application in the front window TFHs used in automobiles.     

Carbon black thin films with tunable resistance and optical transparency

Layer-by-layer assembly was used to produce highly conductive thin films of carbon black and polymer. Positively and negatively-charged polyelectrolytes, polyethylenimine (PEI) and poly(acrylic acid) (PAA), were used to stabilize carbon black in aqueous mixtures that were then deposited onto a PET substrate. The effects of sonication and pH adjustment of deposition mixtures on the conductivity and transparency of deposited films was studied, along with drying temperature. Sonication and oven drying at 70 °C produced films with the lowest sheet resistance (∼1500 Ω/sq), which is a bulk resistivity below 0.2 Ω cm for a 14-bilayer film that is 1.3 μm thick. These two variables improve packing and connectivity amongst carbon black particles that results in increased electrical conductivity. Increasing the pH of the PAA-stabilized mixture and decreasing the pH of the PEI-stabilized mixture resulted in transparent films due to increased polymer charge density. These pH-adjusted films have much higher sheet resistance values than their non-adjusted counterparts due to their reduced thickness and patchy deposition. Varying the number of bilayers allows both sheet resistance and optical transparency to be tailored over a broad range. Carbon black-filled thin films able to achieve these levels of resistivity and transparency may find application in a variety of optoelectronic applications.     

Improved mechanical properties of SnO2:F thin film by structural modification

This study reports the improvement in the mechanical properties of SnO₂:F (FTO) thin films through the modification of the structure and surface morphology. The FTO thin films are deposited on glass substrates by the atmospheric pressure chemical vapor deposition method on an industrial production line. Both the average grain size and the surface roughness were progressively increased by increasing the flow rate of metal organic monobutyltin trichloride (MBTC). The hardness and Young's modulus of the FTO films increased from 9.01 GPa to 15.08 GPa, and from 125.24 GPa to 206.93 GPa, respectively, according to the nanoindenter results. Post-heat treatment at 650 °C for 10 min resulted in a further increase in the hardness and Young's modulus, reaching maximum values of ~15.89 GPa and ~235.9 GPa, respectively. The enhancement in mechanical properties can be attributed to the reduced grain boundaries and the improved structural densification.     

Ag mesh network framework based nano composite for transparent conductive functional electrodes for capacitive touch sensor and thin film heater

We report on the development of a highly conductive, transparent and flexible Ag mesh-like network covered by an ITO/PEDOT:PSS nanocomposite for flexible conductive electronics. The electrode was deposited completely via solution-based deposition. A lower R_s value, from 7.21 Ω/□ to 5.05 Ω/□, was achieved by annealing the substrate via low-temperature plasma annealing. The low-temperature annealing was used to achieve crystallinity of the materials without deformation and degradation of PEDOT:PSS and the PET substrate. The low-cost deposition-based Ag NW-ITO/PEDOT:PSS electrode substantially decreased sheet resistance and provides the transmittance of 85.17%. The chemical stability and mechanical stability of the product were examined, and morphological studies were performed; in all of these, the substrate exhibited excellent behavior. Finally, a transparent flexible electrical heater and capacitive touch screen panel were fabricated using the Ag NW-ITO/PEDOT:PSS electrode to demonstrate the performance of the electrode and its potential applications.     

High tunability in (1 1 0)-oriented BaZr0.2Ti0.8O3 (BTZ) lead-free thin films fabricated by pulsed laser deposition

Using a pulsed laser deposition method the BaZr_0.2Ti_0.8 O₃ (BTZ) lead–free thin films with a thickness of ~250 nm were grown on FTO, ITO and Pt–Si substrates, respectively. The analysis results of microstructural, dielectric properties and leakage current reveal that the thin films deposited on Pt–Si substrates are oriented growth along the (1 1 0) direction and exhibit the optimal performance characteristics. Calculations of figure of merit (FoM) and dielectric tunability display a maximum value of ~42.8 and ~68.5% at E = 400 kV/cm at room temperature, respectively. The excellent tunable properties, high dielectric constant (~635@ 100 kHz) and low leakage current density of (9.3 × 10^–8 A/cm² at 400 kV/cm) make the (1 1 0)–oriented BaZr_0.2Ti_0.8 O₃ thin film to be an attractive material for applications of tunable devices.     

A flexible carbon counter electrode for dye-sensitized solar cells

A pure carbon counter electrode (CE) for dye-sensitized solar cells (DSCs), has been fabricated using an industrial flexible graphite sheet as substrate and activated carbon as the catalytic material. The CE shows very low series resistance (Rs) and charge-transfer resistance (Rct) by combining the high conductivity of the flexible graphite with the high catalytic property of activated carbon. The Rs and Rct for the CE are respectively only a quarter and two-thirds of those for a platinized fluorine-doped tin oxide glass (Pt/FTO). DSCs with cell areas of 0.15 and 1 cm² fabricated with this CE show higher solar-to-electricity conversion efficiencies. The respective values are 6.46% and 5%, compared with 6.37% and 2.91% for the Pt/FTO based devices.     

Studies of electrochemically deposited poly(N-methyl aniline) films

The effect of surface resistance of substrate and concentration of monomer on the properties of electrochemically deposited poly(N-methyl aniline) films has been investigated. The UV–visible spectra of the films show enhanced selectivity in the formation of the conducting phase (approximately 860nm) of polymer on lower surface resistance substrate (10Ω/□) over those with higher surface resistance (50Ω/□). The magnitude of selectivity increases with concentration of monomer. These results are further supported by IR analysis of the samples. From morphological studies it is noted that the films deposited on 10Ω/□ substrates exhibit an overall granular nature irrespective of concentration of monomer. In the case of films deposited on 50Ω/□ substrates sequential changes in patterning are observed with increasing concentration of monomer. Two redox couples are observed in the cyclic voltammograms together with distortion of peak potential in the films obtained on higher surface resistance substrates. © SCI 1998.     

溶液组成对喷雾热解法制备氟掺杂二氧化锡导电薄膜性能的影响

以四氯化锡和氟化铵为原料,异丙醇和水为溶剂,采用喷雾热解法,在载玻片上制备氟掺杂二氧化锡导电薄膜(fluorine-doped tin oxide,FTO)。研究了四氯化锡浓度、氟化铵浓度、双氧水浓度、异丙醇与水的体积比对FTO薄膜的透光率和方块电阻的影响。运用X射线衍射仪、扫描电子显微镜、紫外-可见分光光度计和四探针测试仪分别对FTO薄膜进行了表征。结果表明:在喷雾热解液中加入少量的H2O2(0.05mol/L)可明显提高FTO薄膜在可见光区的透光率,而不影响其方块电阻;当喷雾热解液组成为0.8mol/LSnCl4,0.1mol/LNH4F,0.05mol/LH2O2,异丙醇与水的体积比为8:2,衬底温度为500℃,喷涂100次时,所得FTO薄膜在可见光区的平均透光率为84%,方块电阻为15Ω/□,且FTO薄膜平整致密、二氧化锡晶粒均匀。     

Effects of process parameters on sheet resistance uniformity of fluorine-doped tin oxide thin films

An alternative indium-free material for transparent conducting oxides of fluorine-doped tin oxide [FTO] thin films deposited on polyethylene terephthalate [PET] was prepared by electron cyclotron resonance - metal organic chemical vapor deposition [ECR-MOCVD]. One of the essential issues regarding metal oxide film deposition is the sheet resistance uniformity of the film. Variations in process parameters, in this case, working and bubbler pressures of ECR-MOCVD, can lead to a change in resistance uniformity. Both the optical transmittance and electrical resistance uniformity of FTO film-coated PET were investigated. The result shows that sheet resistance uniformity and the transmittance of the film are affected significantly by the changes in bubbler pressure but are less influenced by the working pressure of the ECR-MOCVD system.