CZTS thin films on transparent conducting electrodes by electrochemical technique

We have fabricated single phase Cu₂ZnSnS₄ (CZTS) films using a specially designed 3-stage electrochemical system. Sequential electrodepositon of constituent metallic layers was carried out on SnO₂/F coated glass substrates using a platinum counter electrode and a saturated calomel reference electrode. Unique bath compositions were formulated for each of these constituents. Sequentially deposited tri-layer stacks were annealed in sulfur environment to get CZTS phase. Detailed structural, morphological and optical characterization experiments were performed using several techniques including x-ray diffraction, Raman and UV-visible spectroscopy, scanning electron microscopy and atomic force microscopy. All characterization experiments indicated that the films are single phase with a measured direct band gap of 1.5 eV.     

Polarization and incidence angle-dependent transmittance of transparent nickel electrodes with various thicknesses

The polarization and incidence angle-dependent transmittance of thin nickel film with various thicknesses deposited on glass substrates was first investigated by using a modified UV-Vis spectrometer. The thin nickel films showed relatively high uniform transmittance over a wide range of wavelengths, 300-1100 nm. The thickness-dependent dielectric and optical constants extracted from the experimental transmittance are significantly distinct from those of the thick nickel film. In particular, the p-polarized light transmittance largely increases with larger incidence angle, but the s-polarized light transmittance behavior is opposite from that of p-polarized light. The difference of the polarization-dependent transmittance increases parabolically with the incidence angle.     

Development of ZTO/Ag/ZTO transparent electrodes for thin film solar cells

Journal of Materials Science: Materials in Electronics - This article presents the optimization of Zinc Tin Oxide/Silver/Zinc Tin Oxide (ZTO/Ag/ZTO) multilayers to implement them in thin film solar...     

Copper doped nickel oxide transparent p-type conductive thin films deposited by pulsed plasma deposition

Transparent p-type conductive Ni_0.9Cu_0.1O thin films were prepared by pulsed plasma deposition (PPD) method. The effects of substrate temperature and oxygen pressure on the structural, electrical and optical properties of the films were investigated respectively. The film deposited at room temperature exhibits the highest conductivity of 5.17 S cm⁻¹, with an average transmittance of 60% in the visible region. A transparent p-Ni_0.9Cu_0.1O/n-In₂O₃:W (IWO) hetero-junction diode was fabricated exhibiting rectifying current-voltage characteristics.     

Solution-processed metal nanowire mesh transparent electrodes

Transparent conductive electrodes are important components of thin-film solar cells, light-emitting diodes, and many display technologies. Doped metal oxides are commonly used, but their optical transparency is limited for films with a low sheet resistance. Furthermore, they are prone to cracking when deposited on flexible substrates, are costly, and require a high-temperature step for the best performance. We demonstrate solution-processed transparent electrodes consisting of random meshes of metal nanowires that exhibit an optical transparency equivalent to or better than that of metal-oxide thin films for the same sheet resistance. Organic solar cells deposited on these electrodes show a performance equivalent to that of devices based on a conventional metal-oxide transparent electrode.     

Emerging transparent electrodes based on thin films of carbon nanotubes, graphene, and metallic nanostructures

Transparent electrodes are a necessary component in many modern devices such as touch screens, LCDs, OLEDs, and solar cells, all of which are growing in demand. Traditionally, this role has been well served by doped metal oxides, the most common of which is indium tin oxide, or ITO. Recently, advances in nano-materials research have opened the door for other transparent conductive materials, each with unique properties. These include CNTs, graphene, metal nanowires, and printable metal grids. This review will explore the materials properties of transparent conductors, covering traditional metal oxides and conductive polymers initially, but with a focus on current developments in nano-material coatings. Electronic, optical, and mechanical properties of each material will be discussed, as well as suitability for various applications.     

Optical anisotropy in single-walled carbon nanotube thin films: implications for transparent and conducting electrodes in organic photovoltaics

Optical anisotropy in single-walled carbon nanotube thin film networks is reported. We obtain the real and imaginary parts of the in-(parallel) and out-of-plane (perpendicular) complex dielectric functions of the single-walled carbon nanotube (SWNT) thin films by combining transmission measurements at several incidence angles with spectroscopic ellipsometry data on different substrates. In sparse networks, the two components of the real part of the complex dielectric constant (epsilon1 parallel and epsilon1 perpendicular) were found to differ by 1.5 at 2.25 eV photon energy. The resulting angular dependence (from 0 to 70 degrees incidence angles) of transmittance is reflected in the conversion efficiency of organic solar cells utilizing SWNT thin films as the hole conducting electrodes. Our results indicate that, in addition to the transparency and sheet resistance, factors such as the optical anisotropy must be considered for optical devices incorporating SWNT networks.     

Optically transparent carbon nanowire thin film

Thin films of amorphous carbon nanowire (a-CNW) have been fabricated from crossed multi-walled carbon nanotube (MWCNT) thin film. The fabrication was done by means of ion beam irradiation on various substrates. It is found that the a-CNW thin films show electrical conduction behaviour, and electrical conductivity varies after annealing. In addition, the transmission spectra in the visible range reveal that the film has above 90% optical transmission. It can be ascribed to the fact that the decreased crystallinity of MWCNTs by ion beam irradiation has caused the incremental increase of optical transmission. We also report on a method for cutting or destroying a-CNWs using low-energy focused electron beam from a scanning electron microscope.     

Intrinsically stretchable transparent electrodes based on silver-nanowire-crosslinked-polyacrylate composites

Stretchable transparent composites have been synthesized consisting of a silver nanowire (AgNW) network embedded in the surface layer of a crosslinked poly(acrylate) matrix. The interpenetrating networks of AgNWs and the crosslinked polymer matrix lead to high surface conductivity, high transparency, and rubbery elasticity. The presence of carboxylic acid groups on the polymer chains enhances the bonding between AgNWs and the polymer matrix, and further increases the stretchability of the composites. The sheet resistance of the composite electrode increases by only 2.3 times at 50% strain. Repeated stretching to 50% strain and relaxation only causes a small increase of the sheet resistance after 600 cycles. The morphology of the composites during reversible stretching and relaxation has been investigated to expound the conductivity changes.     

超疏水性透明涂层的研究进展

超疏水性固体表面是指表面对水的接触角在150°以上,前进接触角和后退接触角的差＜10°的固体表面.超疏水性透明涂层具有自清洁的表面性能,在许多领域具有潜在的应用价值.本文就超疏水性透明涂层研究的理论发展和该领域近年来取得的一些重要研究成果进行评述,并扼要分析了该领域今后的发展方向.     

High quality transparent conductive electrodes in organic photovoltaic devices

The use of indium tin oxide (ITO) in conjunction with polymeric substrates requires deposition at low temperatures or room temperature, and with a limited or no thermal treatment. This process results in high resistivity materials. To achieve practical resistivity levels, we replaced ITO, the workhorse in organic optoelectronic devices, with an ITO/Ag/ITO tri-layer anode. This material yielded the desired electrical properties without a significant effect on its optical properties. For example, a sheet resistance of 15 Ω/□ and an optical transmission of 90% at 550 nm were obtained for a tri-layer film in which thickness of each ITO layer is 50 nm and the Ag layer thickness is 8 nm. The use of these tri-layer anodes in CuPc-C₆₀-based organic solar cells led to an increase in the fill factor under illumination, and thus an improvement of the external power conversion efficiency.     

Fabrication of silver nanowire transparent electrodes at room temperature

Silver nanowires (AgNWs) surrounded by insulating poly(vinylpyrrolidone) have been synthesized by a polyol process and employed as transparent electrodes. The AgNW transparent electrodes can be fabricated by heat-treatment at about 200 °C which forms connecting junctions between AgNWs. Such a heating process is, however, one of the drawbacks of the fabrication of AgNW electrodes on heat-sensitive substrates. Here it has been demonstrated that the electrical conductivity of AgNW electrodes can be improved by mechanical pressing at 25 MPa for 5 s at room temperature. This simple process results in a low sheet resistance of 8.6 Ω/square and a transparency of 80.0%, equivalent to the properties of the AgNW electrodes heated at 200 °C. This technique makes it possible to fabricate AgNW transparent electrodes on heat-sensitive substrates. The AgNW electrodes on poly(ethylene terephthalate) films exhibited high stability of their electrical conductivities against the repeated bending test. In addition, the surface roughness of the pressed AgNW electrodes is one-third of that of the heat-treated electrode because the AgNW junctions are mechanically compressed. As a result, an organic solar cell fabricated on the pressed AgNW electrodes exhibited a power conversion as much as those fabricated on indium tin oxide electrodes. These findings enable continuous roll-to-roll processing at room temperature, resulting in relatively simple, inexpensive, and scalable processing that is suitable for forthcoming technologies such as organic solar cells, flexible displays, and touch screens.      

Hybrid graphene-NiW nanofiber transparent electrodes for all-nanofiber-based pressure sensor

Alloying technique as an ancient and practical instrument has been a diverse fabricator for desirable properties of materials. Herein, utilizing the alloying engineering, we have developed a two-step process for hybrid graphene-NiW nanofibers (Gr-NiW NFs) transparent electrodes. Further analysis reveals that alloying NiW NFs significantly improve their mechanical performance, reducing the growth temperature of graphene down to?~?700 °C or below, which is far less than that of?~?1000 °C for graphene grown on Cu or Pt. More importantly, such Gr-NiW network has exhibited excellent transmittance in a broad wavelength and remarkable conductivity, which, in turn, could be tailored by the growth temperature and the W content. A high transmittance (84.2% at 550 nm) and low sheet resistance (125.4 Ohm/square) were observed at Ni NFs with 5 wt% W. The combination of excellent conductivity, high transparency and mechanical tunability makes it a promising candidate for wearable electronics and optoelectronics. Finally, an all-nanofiber-based pressure sensor on sandwiched Gr-NiW/P(VDF-TrFE)/Gr-NiW NFs was demonstrated, with high sensitivity (0.61 mV kPa^?1) and excellent operation stability. This work offers deep insights into the development of transparent graphene-based electrodes via alloy engineering.

     

High performance metal microstructure for carbon-based transparent conducting electrodes

In this work, a metal busbar microstructure is introduced to decrease the effective sheet resistance of both graphene and carbon nanotube films to a value suitable for use as transparent conducting electrodes (TCEs). The proposed busbar architecture, implemented with Cu, theoretically can reduce the sheet resistance by a factor of 1000, while yet limiting the optical absorption to 4%. Experimental sheet resistance and optical transparency data are presented for two metals with differing contact resistance (Pd and Cu) and for mono- and multi-layer graphene as well as nanotube films. It is found that the metal busbar microstructure decreases the sheet resistance by a factor of 8 and 70 on graphene and nanotube films respectively, a sufficient resistance reduction to enable utilization as a TCE. The contact resistance between the metal grid and carbon film is believed to limit the ultimate performance. The metal busbar microstructure provides a viable route to the use of carbon films in photovoltaic and display applications.     

Electrospray deposition of silver nanowire films for transparent electrodes

Silver nanowire (AgNWs) films were fabricated as transparent electrodes by electrostatic spray deposition (ESD) at atmospheric pressure and room temperature. The effects of solution concentration, spray flow rate, applied high voltage, and annealing temperature were characterized to obtain uniform films. AgNWs thin film was produced with ca. 20 Ω/[square] sheet resistance and 83% transparency in the visible range. Morphologies, optical and electrical properties, and stabilities of the films were investigated in this work. A maximum ratio of DC to optical conductivity of 288 was achieved in a 120 nm thick AgNW thin film. Chemical stability was evaluated in various solvents and we found that solvents had little effect on conductivity.     

Silicon metal-semiconductor-metal photodetector with zinc oxide transparent conducting electrodes

Transparent conducting oxides thin layers, due to their optical and electrical properties, can be used as transparent electrodes in various optoelectronic devices. We present a metal-semiconductor-metal photodiode (MSM-PD) on silicon as optically active layer with zinc oxide (ZnO) thin layer as interdigitated Schottky transparent electrodes. The advantage of using a ZnO thin layer as Schottky electrodes consists in the improvement of the photoresponse by eliminating the shadowing of the active area by opaque metallic electrodes. ZnO thin layers were deposited on 10 Ω cm resistivity silicon epitaxial wafers by the vacuum thermal evaporation method. High purity metallic powders were mixed with an (Al + Sn)/Zn ratio of 0.03. In order to obtain transparent layers the metallic depositions were thermally treated at 450 °C for 2 h. The Al, Sn co-doped ZnO layers of 0.5-0.8 μm were investigated regarding structural, optical and electrical properties and surface morphology. The obtained thin layers have a high transparency (T > 85%) over a large spectral range and the resistivity is quite low, ρ ~ 10^− 4 Ω cm. The interdigitated Schottky contacts of ZnO were configurated onto the optically active Si layer providing an MSM-PD structure of 0.143 mm² active area and finger spacing and finger width of 6 μm. The optoelectronic characteristics were measured and the Schottky barrier height of 0.62 eV was determined from the current-voltage characteristic. A responsivity of 0.2 A/W at 475 nm and a capacitance of 1.4 pF at 10 V bias were obtained for the MSM-PD structure with transparent conducting ZnO Schottky electrodes.