Conjugated polymer chains have many degrees of conformational freedom and interact weakly with each other, resulting in complex microstructures in the solid state. Understanding charge transport in such systems, which have amorphous and ordered phases exhibiting varying degrees of order, has proved difficult owing to the contribution of electronic processes at various length scales. The growing technological appeal of these semiconductors makes such fundamental knowledge extremely important for materials and process design. We propose a unified model of how charge carriers travel in conjugated polymer films. We show that in high-molecular-weight semiconducting polymers the limiting charge transport step is trapping caused by lattice disorder, and that short-range intermolecular aggregation is sufficient for efficient long-range charge transport. This generalization explains the seemingly contradicting high performance of recently reported, poorly ordered polymers and suggests molecular design strategies to further improve the performance of future generations of organic electronic materials.

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-020288.pdf

A general relationship between disorder, aggregation and charge transport in conjugated polymers

Metal nanowire networks (MNNs) are promising as transparent electrode materials for a diverse range of optoelectronic devices and also work as active materials for electrical heating and electromagnetic interference (EMI) shielding applications. However, the relatively low performance and poor durability of MNNs are limiting the practical application of the resulting devices. Here, we report a controllable approach to enhance the conductivity and the stability of MNNs with their transmittance remaining unchanged, in which reduced graphene oxide conformally wrapped silver nanowire networks (AgNW@rGO networks) are synthesized by selective electrodeposition of GO nanosheets on AgNWs followed by a pulsed laser irradiation treatment. Experimental characterizations and finite-difference time-domain simulations indicate that pulsed laser irradiation at a specific wavelength not only reduces the GO but also welds the AgNWs together through a surface plasmon resonance process. As a result, the AgNW@rGO networks exhibit low sheet resistance of 3.3 Ω/□, average transmittance of 91.1%, and good flexibility. Wrapping with rGO improves the maximum electrical heating temperature of the AgNW network transparent heaters due to the effective suppression of the oxidation and the migration of surface silver atoms. In addition, excellent EMI shielding effectiveness of up to 35.5 dB in the 8.2-12.4 GHz frequency range is obtained as a consequence of the combined effects of dual reflection, conduction loss, and multiple dielectric polarization relaxation processes.

Reduced Graphene Oxide Conformally Wrapped Silver Nanowire Networks for Flexible Transparent Heating and Electromagnetic Interference Shielding

Metal nanowire (MNW)-based transparent electrode technologies have significantly matured over the last decade to become a prominent low-cost alternative to indium tin oxide (ITO). Beyond reaching the same level of performance as ITO, MNW networks offer additional advantages including flexibility and low materials cost. To facilitate adoption of MNW networks as a replacement to ITO, they must overcome their inherent stability issues while maintaining their properties and cost-effectiveness. Herein, the fundamental failure mechanisms of MNW networks are discussed in detail. Recent strategies to computationally model MNWs from the nano- to macroscale and suggest future work to capture dynamic failure to unravel mechanisms that account for convolution of the failure modes are highlighted. Strategies to characterize MNW network failure in situ and postmortem are also discussed. In addition, recent work about improving the stability of MNW networks via encapsulation is discussed. Lastly, a perspective is given on how to frame the requirements of MNW-encapsulant hybrids with reference to their target applications, namely: solar cells, transparent film heaters, sensors, and displays. A cost analysis to comment on the feasibility of implementing MNW hybrids is provided, and critical areas to focus on for future work on MNW networks are suggested.

Failing Forward: Stability of Transparent Electrodes Based on Metal Nanowire Networks.

Flexible transparent electrodes (FTEs) with embedded metal meshes play an indispensable role in many optoelectronic devices due to their excellent mechanical stability and environmental adaptability. However, low‐cost, simple, efficient, and environmental friendly integrated manufacturing of high‐performance embedded metal meshes remains a huge challenge. Here, a facile and novel fabrication method is proposed for FTEs with an embedded metal mesh via liquid substrateelectric‐field‐driven microscale 3D printing process. This direct printing strategy avoids tedious processes and offers low‐cost and high‐volume production, enabling the fabrication of high‐resolution, high‐aspect ratio embedded metal meshes without sacrificing transparency. The final manufactured FTEs with 80 mm × 80 mm embedded metal mesh offers excellent optoelectronic performance with a sheet resistance (Rs) of 6 Ω sq−1 and a transmittance (T) of 85.79%. The embedded metal structure still has excellent mechanical stability and good environmental suitability under different harsh working conditions. The practical feasibility of the FTEs is successfully demonstrated with a thermally driven 4D printing structure and a resistive transparent strain sensor. This method can be used to manufacture large areas with facile, high‐efficiency, low‐cost, and high‐performance FTEs.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/advs.202105331

Directly Printed Embedded Metal Mesh for Flexible Transparent Electrode via Liquid Substrate Electric‐Field‐Driven Jet

Flexible transparent electrodes (FTEs) with an embedded metal mesh are considered a promising alternative to traditional indium tin oxide (ITO) due to their excellent photoelectric performance, surface roughness, and mechanical and environmental stability. However, great challenges remain for achieving simple, cost-effective, and environmentally friendly manufacturing of high-performance FTEs with embedded metal mesh. Herein, a maskless, templateless, and plating-free fabrication technique is proposed for FTEs with embedded silver mesh by combining an electric-field-driven (EFD) microscale 3D printing technique and a newly developed hybrid hot-embossing process. The final fabricated FTE exhibits superior optoelectronic properties with a transmittance of 85.79%, a sheet resistance of 0.75 Ω sq-1 , a smooth surface of silver mesh (Ra  ≈ 18.8 nm) without any polishing treatment, and remarkable mechanical stability and environmental adaptability with a negligible increase in sheet resistance under diverse cyclic tests and harsh working conditions (1000 bending cycles, 80 adhesion tests, 120 scratch tests, 100 min ultrasonic test, and 72 h chemical attack). The practical viability of this FTE is successfully demonstrated with a flexible transparent heater applied to deicing. The technique proposed offers a promising fabrication strategy with a cost-effective and environmentally friendly process for high-performance FTE.

Templateless, Plating‐Free Fabrication of Flexible Transparent Electrodes with Embedded Silver Mesh by Electric‐Field‐Driven Microscale 3D Printing and Hybrid Hot Embossing

/pdf/transparent-heaters-a-review-umiv831ieu.pdf

Transparent Heaters: A Review

Owing to its high conductivity, good flexibility, low-cost, and ease of processing, poly(3,4-ethylenedioxythiophene) (PEDOT) has become a ubiquitous material, with uses in photovoltaics, energy sto...

Insight into the Degradation Mechanisms of Highly Conductive Poly(3,4-ethylenedioxythiophene) Thin Films

Conductive polymers are a very promising alternative for the fabrication of transparent conductive materials. They have many advantages compared to existing materials, like a low-cost and a high flexibility. However, electrical conductivity still needs to be improved. We report a straightforward solution-based approach for the fabrication of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films with conductivity as high as 6046 ± 510 S cm−1, based on accurate water content control during the polymerization step. The crystallinity improvement is evidenced by GIWAXS characterization, and low temperature electrical conductivity measurements give new insights on the transport mechanisms at stake. This very high conductivity is, to our knowledge, the highest reported value for solution-based synthesis of PEDOT based materials.

Amélie Schultheiss

Papers

Transparent Heaters: A Review

Insight into the Degradation Mechanisms of Highly Conductive Poly(3,4-ethylenedioxythiophene) Thin Films

Water content control during solution-based polymerization: a key to reach extremely high conductivity in PEDOT thin films

Electrical and Mechanical Properties of Intrinsically Flexible and Stretchable PEDOT Polymers for Thermotherapy

High performance encapsulation of transparent conductive polymers by spatial atomic layer deposition