Zhaozhao Zhu

Ultrahigh Aspect Ratio Copper-Nanowire-Based Hybrid Transparent Conductive Electrodes with PEDOT:PSS and Reduced Graphene Oxide Exhibiting Reduced Surface Roughness and Improved Stability.

UNLABELLED Copper nanowires (CuNWs) with ultrahigh aspect ratio are synthesized with a solution process and spray-coated onto select substrates to fabricate transparent conductive electrodes (TCEs). Different annealing methods are investigated and compared for effectiveness and convenience. The CuNWs are subsequently combined with the conductive polymer poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) ( PEDOT PSS) or with reduced graphene oxide (rGO) platelets in order to reduce the surface roughness and improve the durability of the fabricated TCEs. Our best-performing PEDOT PSS/CuNW films have optical transmittance T550 = 84.2% (at λ = 550 nm) and sheet resistance Rs = 25 Ω/sq, while our best CuNW/rGO films have T550 = 84% and Rs = 21.7 Ω/sq.

Hybrid transparent conductive electrodes with copper nanowires embedded in a zinc oxide matrix and protected by reduced graphene oxide platelets

Transparent conductive electrodes (TCE) were fabricated by combining three emerging nano-materials: copper nanowires (CuNWs), zinc oxide (ZnO) nano-particulate thin films, and reduced graphene oxide (rGO) platelets. Whereas CuNWs are responsible for essentially all of the electrical conductivity of our thin-film TCEs, the ZnO matrix embeds and strengthens the CuNW network in its adhesion to the substrate, while the rGO platelets provide a protective overcoat for the composite electrode, thereby improving its stability in hot and humid environments. Our CuNW/ZnO/rGO hybrid electrodes deposited on glass substrates have low sheet resistance (Rs ∼ 20 Ω/sq) and fairly high optical transmittance (T550 ∼ 79%). In addition, our hybrid TCEs are mechanically strong and able to withstand multiple scotch-tape peel tests. Finally, these TCEs can be fabricated on rigid glass as well as flexible plastic substrates.

Integration of the inexpensive CuNWs based transparent counter electrode with dye sensitized photo sensors

We demonstrate, a newly developed, inexpensive transparent conducting electrode (TCE) based on copper nanowires (CuNWs) combined with reduced graphene oxide (rGO) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as a cathode for Dye Sensitized Photo Sensors (DSPSs). CuNWs were synthesized and deposited in the form of a layer on glass substrates, followed by deposition of rGO and PEDOT:PSS layers, to fabricate hybrid transparent conducting electrodes (TCEs). The hybrid electrodes exhibited an average sheet resistance of 20 Ω cm−2. These TCEs have been successfully integrated with the DSPSs, which were later evaluated for their performance in terms of photo-conductive sensitivity and responsivity. A significant increase in the current and voltage was observed as a function of elevated light intensity. The average response time and reset time of the DSPSs was found to be 118 ms and 28 ms, respectively. Hence it can be said that the CuNWs/rGO/PEDOT:PSS based transparent conducting electrode could potentially be a viable alternative to the expensive ITO/Pt based cathode, in DSPSs.

Ultra-high aspect ratio copper nanowires as transparent conductive electrodes for dye sensitized solar cells

We report the synthesis of ultra-high aspect ratio copper nanowires (CuNW) and fabrication of CuNW-based transparent conductive electrodes (TCE) with high optical transmittance (>80%) and excellent sheet resistance (Rs <30 Ω/sq). These CuNW TCEs are subsequently hybridized with aluminum-doped zinc oxide (AZO) thin-film coatings, or platinum thin film coatings, or nickel thin-film coatings. Our hybrid transparent electrodes can replace indium tin oxide (ITO) films in dye-sensitized solar cells (DSSCs) as either anodes or cathodes. We highlight the challenges of integrating bare CuNWs into DSSCs, and demonstrate that hybridization renders the solar cell integrations feasible. The CuNW/AZO-based DSSCs have reasonably good open-circuit voltage (Voc = 720 mV) and short-circuit current-density (Jsc = 0.96 mA/cm2), which are comparable to what is obtained with an ITO-based DSSC fabricated with a similar process. Our CuNW-Ni based DSSCs exhibit a good open-circuit voltage (Voc = 782 mV) and a decent short-circuit current (Jsc = 3.96 mA/cm2), with roughly 1.5% optical-to-electrical conversion efficiency.

Sol-gel deposited aluminum-doped and gallium-doped zinc oxide thin-film transparent conductive electrodes with a protective coating of reduced graphene oxide

Abstract. Using a traditional sol-gel deposition technique, we successfully fabricated aluminum-doped zinc oxide (AZO) and gallium-doped zinc oxide (GZO) thin films on glass substrates. Employing a plasma treatment method as the postannealing process, we produced thin-film transparent conductive electrodes exhibiting excellent optical and electrical properties, with transmittance greater than 90% across the entire visible spectrum and the near-infrared range, as well as good sheet resistance under 200  Ω/sq. More importantly, to improve the resilience of our fabricated thin-film samples at elevated temperatures and in humid environments, we deposited a layer of reduced graphene oxide (rGO) as protective overcoating. The stability of our composite AZO/rGO and GZO/rGO samples improved substantially compared to that of their counterparts with no rGO coating.

Sol-gel deposition and plasma treatment of intrinsic, aluminum-doped, and gallium-doped zinc oxide thin films as transparent conductive electrodes

Zinc oxide and aluminum/gallium-doped zinc oxide thin films were deposited via sol-gel spin-coating technique. Employing plasma treatment as alternative to post thermal annealing, we found that the morphologies of these thin films have changed and the sheet resistances have been significantly enhanced. These plasma-treated thin films also show very good optical properties, with transmittance above 90% averaged over the visible wavelength range. Our best aluminum/gallium-doped zinc oxide thin films exhibit sheet resistances (Rs) of ~ 200 Ω/sq and ~ 150 Ω/sq, respectively.

Highly transparent low sheet resistance electrodes for solar cell applications

High aspect ratio copper nanowires were synthesized, using a solution-based approach. The nanowires along with reduced graphene oxide thin films were sprayed onto glass and flexible substrates and later annealed in order to produce transparent conducting electrodes (TCEs). These electrodes exhibited 91.5% optical transmissivity and around 9- Ω/sq sheet resistance, which are comparable to Indium Tin Oxide (ITO). In addition, the hybrid TCEs, when exposed to ambient temperature showed slowed sheet resistance degradation. The electrodes deposited on a flexible substrate, showed immunity against any notable changes in the sheet resistance, when gone through numerous bending cycles. Adaption of such nanomaterials in conducting films could lead to the potential alternatives for the conventional ITO, with applications in numerous industries, including solar cells manufacturing.

Metal nanowire-graphene composite transparent electrodes

Silver nanowires with 40 nm diameter and copper nanowires with 150 nm diameter were synthesized using low-temperature routes, and deposited in combination with ultrathin graphene sheets for use as transparent conductors. A systematic and detailed analysis involving nature of capping agent for the metal nanowires, annealing of deposited films, and pre-treatment of substrates revealed critical conditions necessary for preparing high performance transparent conducting electrodes. The best electrodes show ~90% optical transmissivity and sheet resistance of ~10 Ω/□, already comparable to the best available transparent electrodes. The metal nanowire-graphene composite electrodes are therefore well suited for fabrication of opto-electronic and electronic devices.

Transparent conducting electrodes based on thin, ultra-long copper nanowires and graphene nano-composites

High aspect-ratio ultra-long (> 70 μm) and thin (< 50 nm) copper nanowires (Cu-NW) were synthesized in large quantities using a solution-based approach. The nanowires, along with reduced graphene-oxide sheets, were coated onto glass as well as plastic substrates, thus producing transparent conducting electrodes. Our fabricated transparent electrodes achieved high optical transmittance and low sheet resistance, comparable to those of existing Indium Tin Oxide (ITO) electrodes. Furthermore, our electrodes show no notable loss of performance under high temperature and high humidity conditions. Adaptations of such nano-materials into smooth and ultrathin films lead to potential alternatives for the conventional tin-doped indium oxide, with applications in a wide range of solar cells, flexible displays, and other opto-electronic devices.

Hybrid thin-films of Graphene materials and metallic nanowires for next generation transparent electrodes

We report advances in the fabrication and characterization of transparent conductive electrodes based on thin-films of metallic nanowires (copper and silver) encapsulated with graphene, graphene oxide, and reduced graphene oxide, using solution-processed approaches.