Seyul Kim

Highly reliable AgNW/PEDOT:PSS hybrid films: efficient methods for enhancing transparency and lowering resistance and haziness

Silver nanowires (AgNWs) are remarkable components that may be able to replace indium tin oxide (ITO) as transparent electrodes due to their high DC conductivity and excellent optical transmittance. However, a common coating method can cause detrimental electrical deviation and poor optical properties due to the creation of randomly organized connections of AgNWs. These problems should be overcome in AgNW-based films for transparent and reliable conductive electrodes through material and engineering approaches. In this work, we have demonstrated highly conductive films of an AgNW/PEDOT:PSS composite with excellent optical transparency and good electrical deviation through a multi-layer coating process with a controlled AgNW solution. We studied the effect of the number of coatings and optimized the process for high-performance AgNW/PEDOT:PSS composite films. The resulting film showed 2.3% enhancement at 550 nm in terms of the transmittance and reduction of haziness by approximately two to four percent according to the number of coatings. In addition, the film exhibited an excellent electrical standard deviation of 1.7 Ω sq−1 in all areas of the substrate in a reliability test. The optimized AgNW/PEDOT:PSS film was patterned by photolithography and etching processes to confirm the possibility for electrode applications and the patterned film showed clear 30 μm width line patterns maintaining resistance. These improvements by our method can support a new approach for transparent electrodes with excellent optical and electrical properties using metal-based nanomaterials.

A one-step roll-to-roll process of stable AgNW/PEDOT:PSS solution using imidazole as a mild base for highly conductive and transparent films: optimizations and mechanisms

A recent increase in the demand for transparent electrodes has led to shortage in supply and an increase in the price of indium tin oxide (ITO) films deposited by sputter coating owing to coating speed limitations. Furthermore, flexibility has become one of the essential properties of transparent electrodes, accounting for the rapidly changing trend in electronics. These problems can be overcome by AgNW-based films suitable for flexible and stable conductive electrodes by using wet-coating-processable material and roll-to-roll coating. In this work, we developed an effective method to fabricate a highly conductive, transparent, and stable AgNW/PEDOT:PSS film using roll-to-roll slot-die coating. This coating technique provides higher line speed and greater coating uniformity. Furthermore, the optimized AgNW/PEDOT:PSS solution allows direct one-step coating without any post-treatment, such as high-temperature annealing, mechanical pressure, and solvent washing. We also studied the mechanisms of AgNW corrosion induced by the acidity of PEDOT:PSS and by hydrogen sulfide (H2S) and carbonyl sulfide (OCS) of the atmosphere. Corrosion could be prevented by neutralizing PEDOT:PSS using imidazole, which is a suitable organic compound in terms of both material and processing properties owing to its mild basicity and high melting and boiling points. In addition, the over-coating by a silica-based protecting layer on the AgNW/PEDOT:PSS film resulted in enhanced corrosion protection. The resulting roll film (460 mm in width × 20 m in length) showed suitable electrical (Rs ∼ 75 Ω sq−1) and optical (T > 90% at 550 nm, haziness ∼1.21%, b* ∼ 0.72) properties to replace ITO films in touch screen panels.

Purification of PEDOT:PSS by Ultrafiltration for Highly Conductive Transparent Electrode of All-Printed Organic Devices.

A highly conductive, air stable and scalable poly(3,4-ethylenedioxythiophene) (PEDOT): poly(4-styrenesulfonate) (PEDOT:PSS) are prepared by using mass production ultrafiltration. By effectively removing excess PSS and various reaction impurities using repeated 100 nm pore membrane filtration, purified PEDOT:PSS exhibit conductivity as high as 2000 S cm-1 .

Gradual thickness-dependent enhancement of the thermoelectric properties of PEDOT:PSS nanofilms

We have investigated the thickness-dependent change in the thermoelectric properties of nanofilms of the conducting polymer, PEDOT:PSS. Films with varying thickness were prepared by spin coating the polymer solution at different speeds. Because of its relatively facile processing, good electrical conductivity, and environmental stability, PEDOT:PSS is considered to be one of the most promising candidates for application in thermal to electric energy conversion devices. Electrical conductivity is attributed to the enhanced carrier mobility in the ordered chain structures of the polymer. The Seebeck coefficient is influenced by the energy derivative of electronic energy density. This approach can be used to study the dependence of conductivity and the Seebeck coefficient at room temperature with varying film thickness. Both the conductivity and Seebeck coefficient improved with increasing thickness of the polymer nanofilms. This can be attributed to the change in the conformation of PEDOT, which exposes the PEDOT on the surface of the PEDOT:PSS phase. The PEDOT:PSS thin films were characterized by UV-Vis spectroscopy, tapping-mode atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. This study suggests that variation of film thickness is an effective way of improving the thermoelectric properties of PEDOT:PSS.

Synthesis of conductive and transparent PEDOT:P(SS-co-PEGMA) with excellent water-, weather-, and chemical-stabilities for organic solar cells

The water-, weather- and chemical-resistant conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)-co-poly(ethylene glycol methacrylate) (PEDOT:P(SS-co-PEGMA)) copolymer was successfully synthesized with thermally curable P(SS-co-PEGMA) copolymers. The PSS and P(SS-co-PEGMA) copolymers were synthesized by solution polymerization and PEDOT:PSS and PEDOT:P(SS-co-PEGMA) were synthesized by Fe+-catalyzed oxidative polymerization. PSS and P(SS-co-PEGMA) were characterized by Fourier-transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (NMR). The electrical properties of the conductive PEDOT:P(SS-co-PEGMA) thin films were characterized in two parts; first, the mechanism and characterization of the conductivity change, and second, the characterization of the water-, chemical-, and weather-stability of the films. The conductivity and transmittance, respectively, of PEDOT:P(SS-co-PEGMA) at 550 nm under optimized conditions were maintained at the levels found in PEDOT:PSS, 160.3 S cm−1 and 86.7%. The introduction of PEGMA to the PSS copolymer improved the mechanical properties and weather stability. The PEDOT:P(SS-co-PEGMA) was highly stable to chemical solvents and independent of the type of solvents used for stability analysis. The conductivity in the weather stability test of PEDOT:PSS decreased by 44.9%, on the other hand, the conductivity of PEDOT:P(SS-co-PEGMA) was decreased by only 22.2%. The PEDOT:PSS and PEDOT:P(SS-co-PEGMA) copolymers were used as buffer layers in organic solar cells (OSC) and showed as high efficiency as conventional PEDOT:PSS materials. The decrease of OSC efficiency with PEDOT:P(SS-co-PEGMA) was 30% less than the OSCs with the commercial and reference PEDOT:PSS buffer layers.

Multi-purpose overcoating layers based on PVA/silane hybrid composites for highly transparent, flexible, and durable AgNW/PEDOT:PSS films

Flexible hybrid overcoating layers with antireflective properties are fabricated by a catalyzed two-step sol–gel process using poly(vinyl alcohol) (PVA) and silane precursors, followed by simple bar coating. Hydrolysis of alkoxysilanes followed by the condensation reaction forms chemical bonds between Si–OH and C–OH groups. A glass substrate with the hybrid overcoating layer shows higher transmittance than a bare glass substrate because the overcoating provides an antireflective layer with an intermediate refractive index. Haziness and surface roughness of the hybrid overcoating decrease with increasing PVA content. Further, complexation of PVA and silanes yields greater mechanical flexibility. Various silanes functionalized with methyl, epoxy, amino, and phenyl groups are also incorporated into the hybrid overcoating to adjust the hydrophobicity, transparency, and protective properties. A methyltrimethoxysilane (MTMS)-based hybrid overcoating shows the best optical transparency and water repellency. Application of a PVA/MTMS hybrid overcoating over silver nanowire (AgNW)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) conducting films dramatically improves the long-term stability of the sheet resistance through enhanced resistance to moisture penetration. Consequently, highly stable and durable AgNW/PEDOT:PSS conducting films (sheet resistance, 20 Ω sq−1; transmittance, 95.4%) are fabricated by passivating them on both sides with the hybrid overcoating.