Solvent Post-treatment Research Articles

AgNWs self-assembly along coaxially electrospun SEBS-PVP core-sheath fibers for stretchable conductive membranes with low interfacial losses

In this paper, core-sheath fibers with poly(styrene-ethylene/butylene-styrene) triblock copolymer (SEBS) as the core layer and polyvinylpyrrolidone (PVP) of different molecular weights as the sheath layer were prepared by coaxial electrospinning. Amphiphilic triblock copolymers were added to the SEBS core layer, and the fusion of incompatible SEBS-PVP at the core-sheath interface was further promoted by appropriate solvent post-treatment. Polydopamine (PDA) was in situ polymerized on the surface of SEBS-PVP fibers, so that silver nanowires (AgNWs) with high aspect ratios were conformally self-assembled along the fibers to form good interfacial bonding, so that the SEBS-PVP/AgNW composite membrane has high conductivity and exhibits good interfacial transfer effect in cyclic stretching under large strain. Based on core-sheath nanofibers and self-assembly, the excellent interfacial transfer gives SEBS-PVP/AgNW low viscoelastic loss, integrated large tensile strain sensing and stable Joule heating effect, which is conducive to the development and application of multifunctional stretchable electronics.

Solvent-Activated Transformation of Polymer Configurations for Advancing the Interfacial Reliability of Perovskite Photovoltaics.

Organic materials have been widely used as the charge transport layers in perovskite solar cells due to their structural versatility and solution processability. However, their low surface energy usually causes unsatisfactory thin-film wettability in contact with the perovskite solution, which limits the interfacial performance of the photovoltaic devices. Although solvent post-treatment could occasionally regulate the wetting behavior of organic films, the mechanism of the solid-liquid interaction is still unclear. Here, we present evidence of a possible correlation between the solvent and the wettability of a conventional polymer, poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA), and reveal the critical roles of Hansen solubility parameters (HSPs) of solvents in wetting mechanisms. Our results suggest that the conventional solvent N,N-dimethylformamide (DMF) improves the wettability of PTAA by the morphological disruption mechanism but negatively impacts interfacial charge collection and stability. In contrast, 2-methoxyethanol (2-Me) with an appropriate HSP value induces the transformation of the PTAA configuration in an orderly manner, which simultaneously improves the wetting property and maintains the film topography. After careful optimization of the surface conformation of the PTAA film, both perovskite crystallization and interfacial compatibility have been enhanced. Benefiting from superior interfacial properties, the perovskite solar cells based on 2-Me deliver a champion efficiency of 24.15% compared to 21.4% for DMF-based ones. More encouragingly, the use of 2-Me minimizes the perovskite buried interfacial defects, enabling the unencapsulated devices to maintain about 95% of their initial efficiencies after light illumination for 1100 h. The present study demonstrates the high effectiveness of solvent-polymer interaction for adjusting interfacial properties and strengthening the robustness of perovskite solar cells.

Biodegradable flexible conductive film based on sliver nanowires and PLA electrospun fibers

AbstractBiodegradable conductive films are crucial for the sustainable development of wearable electronics. In this work, a flexible and degradable conductive film was prepared based on a carefully designed interface of polylactic acid (PLA) electrospun fibers and silver nanowires (AgNWs). The amphiphilic triblock copolymer was added to PLA solution for electrospinning, followed by solvent posttreatment to induce the hydrophilic block of the amphiphilic triblock copolymer to migrate to the fiber surface. Dopamine can be uniformly polymerized on the surface of hydrophilic PLA fibers, and the prepared PLA@PDA fiber film can form a good interface combination with AgNWs. The electrical conductivity of AgNWs/PLA@PDA flexible film can reach 258.5 S cm−1, showing obvious Joule heating effect and good mechanical properties. Degradation experiments showed that in phosphate buffered saline, the PLA molecular chain showed a dynamic equilibrium due to the scission and rearrangement of the ester groups and degraded slowly, while AgNWs/PLA@PDA degraded rapidly under alkaline conditions. Our study provides a simple and controllable method to prepare flexible degradable electronic films, which is expected to be applied to flexible wearable bioelectrodes.

Are Hansen solubility parameters relevant in predicting the post-treatment effect on polyamide-based TFC membranes?

This study investigates the impact of solvent post-treatment on polyamide-based thin film composite (TFC) membranes, specifically examining the effect on commercial nanofiltration (NF) and reverse osmosis (RO) membranes. Na2SO4 rejection and increase in pure water permeance (PWP) were considered as the output parameters. The disparity in Hansen solubility parameters (HSP) between the post-treatment solution and the polyamide layer of the TFC membrane, denoted by Ra, is well adapted to understand the enhancement in water permeance through the membranes upon treatment. Aqueous solutions of dimethylformamide with a Ra value of 4, acetonitrile with a Ra value of 8.3, and ethanol with a Ra value of 12.7 were used as the post-treatment solutions. Our experimental design, based on the Box-Behnken design of Response Surface Methodology, incorporates variables such as the concentration of the solvent in the solution (% v/v), Ra value, and treatment time (s). Our findings demonstrate that the effect of post-treatment on the TFC membranes is not governed by the Ra value. Notably, while the post-treatment with the aqueous solution of acetonitrile, 80% v/v for 30 s, had considerable effects on NF membranes (124.5% enhancement in PWP; reduction of 3.5% in Na2SO4 rejection), its impact on RO membranes was negligible. Several factors explain this discrepancy, including the limitations of the HSP model for composite polymers, the inaccuracy of the PWP or salt rejection as a swelling indicator, variations in the HSP values of the polyamide layers for different membranes, and possible modifications in the interface between the support membrane and the polyamide layer. In summary, our study provides insights into the complex interactions between solvents and composite membranes, indicating that HSP alone is not a decisive factor in predicting post-treatment effects on polyamide-based TFC membranes.

Enhancing the Conductivity of PEDOT:PSS Films by the Confinement of Ice Crystals.

Rapid developments in organic electronics demand highly conductive and freestanding (PEDOT:PSS) films. However, the synthesis of highly conductive PEDOT:PSS films requires toxic reagents, such as high-concentration acids and bases. Herein, an eco-friendly and cost-effective strategy is reported for improving the conductivity of PEDOT:PSS films through the confinement of ice crystals. The crystallization of water swelled by the film facilitated the phase separation of PEDOT and PSS, and the excess PSS in the skin layer is effectively removed. Moreover, under the confinement effect, the carrier mobility of the film is enhanced through the formation of a well-crystallized PEDOT molecular morphology. A detailed elucidation of aggregate structure evolution in PEDOT:PSS films during annealing, solvent post-treatment, and subsequent confined crystallization is presented herein. After multiple water crystallization cycles, the conductivity of the PEDOT:PSS film increased by over 85%, achieving a maximum of 2564±142Scm-1. Finally, compared to post-treatment with dimethyl sulfoxide (DMSO), the current strategy can improve the Seebeck coefficient by 5.6% and the power factor by 139%.

Engineering CsPbBr3 perovskite from 2D nanoplatelets to 0D quantum dots via polar solvent post-treatment

Cesium lead halide (CsPbX3 X = I, Br, Cl) perovskites have potential applications in the fields of X-ray fluorescence imaging, solar cells, light-emitting diodes (LEDs) and photocatalysis due to their excellent optical and electrical properties. In this work, we propose a novel method to tune the emission color of CsPbBr3 by polar solvent post-treatment. The blue emission color of the two-dimensional (2D) CsPbBr3 nanoplatelets (NPLs) prepared at room temperature is evidently changed to green under UV excitation via DMF post-treatment. We verify the DMF is used to decompose these NPLs into 0D quantum dots followed by the color variation. We further reveals the polarity of the employed solvent is the main parameter in the decomposition processes. This novel route might be suitable for other 2D perovskites and benefit the application of these colorful products in LEDs and information storage fields.

Aggregate structure evolution induced by annealing and subsequent solvent post-treatment for thermoelectric property enhancement of PEDOT:PSS films

• Effect of aggregation structure evolution on thermoelectric performance is studied. • Thermal annealing induces notably increased PEDOT crystallinity. • Solvent treatment affects nanofibril formation, edge-on stacking, phase separation. • Power factor of the treated film is 216 times of that of the pristine. Organic polymer thermoelectric (TE) materials have developed rapidly in recent years in terms of strategies to improve their TE performance. However, the effect of molecular mechanisms on their TE performance remains yet to be unveiled. Insights into the evolution of crystalline microstructures of conjugated polymers are critical in determining their aggregate structure and hence their TE performance. Herein, an effective approach has been developed to modify the aggregate structures of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). During annealing and subsequent solvent post-treatment, phase separation between the conductive PEDOT and the insulating PSS occurs and the excess PSS in the skin layer is effectively removed. As a result, carrier mobility and carrier concentration are synergistically boosted via the formation of well-crystallized molecular morphology and the increase of PEDOT doping level, leading to significantly enhanced TE performance with an unprecedented power factor that is 216 times of that of the pristine samples. The corresponding molecular mechanisms are discussed in detail and the aggregate structure evolution route is thoroughly proposed. It is believed that the aggregate structure evolution proposed in this work and its influential mechanisms on TE performance can be extended to other polymers and potentially direct the future design of high-performance polymer-based TE materials.

Manipulation of PEDOT:PSS with Polar and Nonpolar Solvent Post-treatment for Efficient Inverted Perovskite Solar Cells

Poly(3,4–ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has been widely used as a hole conducting polymer in many optoelectronic devices including perovskite solar cells. However, its ...

Two-step solvent post-treatment on PTAA for highly efficient and stable inverted perovskite solar cells

Modifying the surface of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) with toluene during the high-speed spin-coating process of dimethylformamide considerably improves the wettability and morphology of PTAA and results in improvement of the crystallinity and absorption of perovskite film. The hole mobility and ohm contact have also been improved accordingly. Combined with these improved parameters, inverted perovskite solar cells with high efficiency of 19.13% and long-term stability could be achieved, which are much better than those with untreated PTAA. Importantly, our devices can keep 88.4% of the initial power conversion efficiency after 30 days of storage in ambient air.

Organic/inorganic hybrid for flexible thermoelectric fibers

Fiber-based flexible thermoelectric (TE) generators are highly desirable for their capability of converting electricity from thermal energy and their potential applications in wearable and portable electron devices. Herein, by inducing the gelation of conducting polymer PEDOT:PSS, we successfully prepared PEDOT:PSS/tellurium nanowires (PEDOT:PSS/Te-NWs) organic/inorganic hybrid fibers for flexible TE generator without substrates. In this work, the higher TE performance of hybrid fibers were achieved compared to its individual components. Further, solvent post-treatment was employed as an effective strategy to enhance the TE performance and mechanical properties of the as-fabricated hybrid fibers. Therefore, a power factor as high as 17.8 μW m−1 K−2 with good mechanical stability was realized for H2SO4 post-treated PEDOT:PSS/Te-NWs hybrid fiber with 50 wt% of Te-NWs. Additionally, a simple flexible TE generator with six pairs of p-n fiber legs with this post-treated hybrid fibers and carbon nanotube fibers (CNFs) was fabricated and showed the acceptable power density. This work may share lights on the development of organic/inorganic hybrid fiber-based flexible energy generators.

Impacts of secondary solvents on morphology and charge transport of conjugated polymer thin films

Secondary solvents are utilized in post-processing procedures, such as the solvent post-treatment and post-deposition of polymer protecting and dielectric layers, and their effects on the morphology, molecular ordering, and charge-transport characteristics of poly (3-hexylthiophene) (P3HT) thin films have been investigated by systematically varying the polarity, viscosity, and solubility of co-solvent systems (i.e., chloroform/hexane, chloroform/methanol, and DCB/n-heptanol). During the solvent post-treatment, the P3HT films are preferentially dissolved by a co-solvent in the following order: DCB/n-heptanol < chloroform/methanol < chloroform/hexane co-solvent system. The chloroform/hexane blend with a lower polarity preferably dissolved the P3HT films compared to the chloroform/methanol blend with a higher polarity owing to a better compatibility with non-polar hexyl side chains of P3HT. The chloroform/methanol blend, which has a relatively low viscosity, was found to be more effective for the dissolution of the P3HT films than the DCB/n-heptanol blend, which has a high viscosity, owing to its faster diffusion and better wettability. Interestingly, it was revealed that co-solvent systems increasingly facilitate the rearrangement of P3HT chains with a decrease in the RED values (i.e., increase in solubility), resulting in enhanced intra- and intermolecular interactions of P3HT films. Meanwhile, the crystal grain size of the P3HT films did not noticeably vary. Consequently, as the relative energy difference (RED) values of secondary co-solvents decreased, the average mobility of the P3HT films increased in the following order: DCB/n-heptanol < chloroform/methanol < chloroform/hexane. Further, we apply secondary solvents to the post-deposition of polymer protecting layers and dielectric layers, and study their effects on the conjugated polymer films. In contrast with the case involving solvent post-treatment, the secondary co-solvents used in the case of the post-deposition of either a polymer protecting or dielectric layer (i.e., poly (methyl methacrylate) (PMMA)) very slightly affected the molecular ordering, morphology, and charge-transport properties of the P3HT films for solvent RED values ranging from 1.2 to 1.8; this is because of the attenuated interactions between the solvent and P3HT molecules by the PMMA molecules, which indicates that the spectrum of secondary solvent systems and polymers that are applicable to the deposition of protecting polymer and dielectric layers can be expanded.

Effect of solvents treatment on the electrical stability and surface wetting properties of PEDOT:PSS thin films

Solvent post-treatment of PEDOT:PSS conductive thin films have been shown to be an effective way to improve their electrical conductivity. However, such treatment could also have an impact on the performance stability and surface properties of PEDOT:PSS films. In the current work, PEDOT:PSS samples were prepared with different thicknesses and treated using a simple solvent post-treatment method. The electrical performance stability of the solvent post-treated films was investigated over prolonged time period. The electrical stability of the studied samples shows some dependence on their thickness. Moreover, reduced electrical performance degradation was noticed after solvent treatment. An alteration in the films wetting-dewetting properties after the treatment was also observed. The correlation between the surface properties and the improved performance stability of the treated PEDOT:PSS films is discussed in the light of the obtained results. Some remarks on the impact of solvent treatment on the performance of the treated-PEDOT:PSS films based devices are also given.

High performance ITO-free white organic light-emitting diodes using highly conductive PEDOT:PSS transparent electrodes

We report high performance white organic light-emitting diodes (OLEDs) based on high conductivity poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films optimized by a solvent post treatment. The device stack is carefully optimized with high efficiency tandem structures including red, yellow/green, and blue emissive materials. The OLED with the PEDOT:PSS transparent electrode achieves a high power efficiency of 26.1 lm/W and an external quantum efficiency of 19.3%, which are comparable to the reference indium tin oxide (ITO)-based OLEDs. In addition, it is observed that the angular emission characteristic of PEDOT:PSS-based OLEDs is closer to Lambertian distribution compared to that of the ITO-based OLED. We show that the optimized device stack together with post-treated PEDOT:PSS transparent electrodes can realize high performance ITO-free white OLEDs.

Catalytic Activity Control via Crossover between Two Different Microstructures.

Metal nanocatalysts hold great promise for a wide range of heterogeneous catalytic reactions, while the optimization strategy of catalytic activity is largely restricted by particle size or shape control. Here, we demonstrate that a reversible microstructural control through the crossover between multiply twinned nanoparticle (MTP) and single crystal (SC) can be readily achieved by solvent post-treatment on gold nanoparticles (AuNPs). Polar solvents (e.g., water, methanol) direct the transformation from MTP to SC accompanied by the disappearance of twinning and stacking faults. A reverse transformation from SC to MTP is achieved in nonpolar solvent (e.g., toluene) mixed with thiol ligands. The transformation between two different microstructures is directly observed by in situ TEM and leads to a drastic modulation of catalytic activity toward the gas-phase selective oxidation of alcohols. On the basis of the combined experimental and theoretical investigations of alcohol chemisorption on these nanocatalysts, we propose that the exposure of {211}-like microfacets associated with twin boundaries and stack faults accounts for the strong chemisorption of alcohol molecules on MTP AuNPs and thus the exceptionally high catalytic activity.

Enhanced electrical properties of PEDOT:PSS films using solvent treatment and its application to ITO-free organic light-emitting diodes

Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films are prepared by introducing a new solvent 2-ethoxyethanol and are optimized by acid-free solvent post treatment. The behavior of samples are investigated with various coating conditions. The change of electrical performance for 2-ethoxyethanol added PEDOT:PSS films with various post treatment methods is studied. Upon post treatment, the sheet resistance greatly decreases attributed to a structural change with removal of insulating PSS in the film. Based on these conductive films, we demonstrate efficient ITO-free green phosphorescent organic light-emitting diodes (OLEDs). The efficiency of OLEDs with post-treated PEDOT:PSS electrodes is greater than that of OLEDs with untreated PEDOT:PSS electrodes. The results illustrate a promising future for flexible, low-cost, ITO-free OLEDs employing PEDOT:PSS electrodes optimized by 2-ethoxyethaol with acid-free solvent post treatment.

Efficient ITO-free organic light-emitting diodes comprising PEDOT:PSS transparent electrodes optimized with 2-ethoxyethanol and post treatment

We demonstrate highly conductive poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) films introduced with a newly investigated solvent 2-ethoxyethanol. The films are optimized by simple solvent post treatment and show enhanced conductivities and reduced sheet resistances. Solvent post treatment for 2-ethoxyethanol added PEDOT:PSS films reduces insulating PSS and forms conductive PEDOT networks in conductive films, resulting in improved electrical properties. ITO-free white OLEDs are fabricated with post-treated PEDOT:PSS electrodes and show almost equal performance to ITO-based OLEDs. Our work demonstrate that the conductive PEDOT:PSS electrode optimized by 2-ethoxyethanol and post treatment promises its potential as alternative transparent electrode in flexible, low-cost, high-performance ITO-free OLEDs.

Highly Conductive PEDOT:PSS Films with 1,3-Dimethyl-2-Imidazolidinone as Transparent Electrodes for Organic Light-Emitting Diodes.

PSS) films as transparent electrodes for organic light-emitting diodes (OLEDs) are doped with a new solvent 1,3-dimethyl-2-imidazolidinone (DMI) and are optimized using solvent post-treatment. The DMI doped PSS films show significantly enhanced conductivities up to 812.1 S cm(-1) . The sheet resistance of the PSS films doped with DMI is further reduced by various solvent post-treatment. The effect of solvent post-treatment on DMI doped PSS films is investigated and is shown to reduce insulating PSS in the conductive films. The solvent posttreated PSS films are successfully employed as transparent electrodes in white OLEDs. It is shown that the efficiency of OLEDs with the optimized DMI doped PSS films is higher than that of reference OLEDs doped with a conventional solvent (ethylene glycol). The results present that the optimized PSS films with the new solvent of DMI can be a promising transparent electrode for low-cost, efficient ITO-free white OLEDs.

솔벤트 도핑과 후처리 공정에 따른 전도성 고분자 PEDOT : PSS의 특성 변화

Poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT : PSS) has attracted a great deal of attention as a transparent conductive material for organic solar cells or organic light-emitting diodes due to its high electrical conductivity, optical trans- parency, and excellent mechanical flexibility. It is well known that a solvent doping for PEDOT : PSS thin-films significantly increases the conductivity of films. In this paper, the effect of various kinds of solvent doping and post-treatment on the electrical and structural properties of PEDOT : PSS thin-films is investigated. The solvent doping greatly increases the con- ductivity of PEDOT : PSS thin-films up to 884 S/cm. A further enhancement of the conductivity of PEDOT : PSS thin-films is achieved by the solvent post-treatment which raises the conductivity up to 1131 S/cm. The enhancement is mainly caused by the depletion of insulating PSS and forming conducting PEDOT-rich granular networks. Strong optical absorption peaks at the wavelength of 225 nm of PEDOT : PSS thin-films indicate the depletion of insulating PSS by post-treatment. We be- lieve that the solvent post-treatment is a promising method to achieve highly conductive transparent PEDOT : PSS thin-films for applications in efficient, low-cost and flexible organic devices.

The optimization of thermoelectric properties in a PEDOT:PSS thin film through post-treatment

Our study shows that by combination of co-solvent and temperature of solvent post treatment method, the highest power factor of 37.05 μW mK−2 is obtained for PEDOT:PSS post-treated with DMSO at 120 °C.