Flexible Organic Electronic Devices Research Articles

Electrical conductivity of polyvinyl alcohol/carboxymethyl cellulose doped by zinc oxide and hematite nanoparticles for optoelectronics devices

This research explores polymer nanodielectrics, a category of materials where nanoceramic fillers are incorporated into polymers. These hybrid materials are gaining significant interest because of their tunable optical and electrical characterization, making them potentially well-suited for applications in flexible optoelectronic and organic electronic devices. Polyvinyl alcohol (PVA), Carboxymethyl cellulose (CMC), zinc oxide (ZnO), and hematite (Fe2O3) nanoparticles were utilized to fabricate PVA/CMC-ZnO/Fe2O3 films XRD analysis indicated a reduction in the crystalline character of the PVA/CMC blend following the doping of ZnO/Fe2O3 nanoparticles (NPs). FTIR data approved the complexation between the PVA/CMC blend and the ZnO/Fe2O3, leading to a decrease in intermolecular interactions within the polymeric matrix and coordination with the ZnO/Fe2O3. Electrical analysis obtained an enhancement in σac values with the increase of ZnO/Fe2O3 NPs concentration up to 30 min of laser ablation times The findings from this study suggest the promise of these materials for applications in high-performance batteries, supercapacitors, or other next-generation energy storage and conversion devices.

Gamma irradiation-induced changes in structural, linear/nonlinear optical, and optoelectrical properties of PVB/BiVO4 nanocomposite for organic electronic devices

Herein, nanocomposite films based on polyvinyl butyral (PVB) and BiVO4 plates were synthesized through solution casting. The present study aims to investigate the impact of varying doses of gamma irradiation (0, 15, 30, 60, and 90 kGy) on the structural, dispersion, linear/nonlinear optical, and optoelectrical properties of PVB/BiVO4 nanocomposite films. The effects of gamma irradiation on various optical characteristics, such as refractive index (n), extinction coefficient (k), and other related parameters, have been observed. The study of dielectric behavior and the derivation of optoelectrical parameters, including high-frequency dielectric constant (ε∞), plasma frequency (ωP), relaxation time (τ), and optical mobility (µopt.), were conducted using the real and imaginary parts of the dielectric constants εr and εi. In addition, the linear optical susceptibility (χ(1)), the third-order nonlinear optical susceptibility (χ(3)), and the nonlinear refractive index (n2) were studied as a function of gamma irradiation doses. Furthermore, the results demonstrate that the average oscillator wavelength (λ0) values, oscillator strength (S0), and optical conductivity (σopt) vary significantly after gamma radiation treatment. Overall, the strong correlations between the linear/nonlinear optical and optoelectrical parameters of the irradiated PVB/BiVO4 nanocomposite films make them suitable for application in flexible organic electronic devices.

Threshold voltage tuning in gelatin biopolymer-gated high-performance organic field-effect transistors

Natural biopolymers have been of considerable interest in developing flexible, biocompatible and biodegradable organic electronic devices. Herein, we demonstrate gelatin biopolymer gated OFETs utilizing thermally evaporated α-sexithiophene (α-6T) and solution-processable poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14) as organic semiconductors (OS). The tunability of threshold voltage (VT) for the OFETs as a function of lithium-perchlorate (LP) content (% w/w) in gelatin is also explored. With the increase of LP (0% to 20% w/w) in the gelatin, VT reduces from − 5.7 V to − 1.75 V and − 2.15 V to + 0.1 V for α-6T and PBTTT-C14 based OFETs, respectively. The highest hole mobility in the saturation regime (μS) of α-6T and PBTTT-C14 is estimated as 2.0 cm2V−1s−1 and 0.1 cm2V−1s−1 respectively with the on/off ratio ∼103. It is ascribed to the efficient formation of an electric double layer (EDL) at the dielectric/organic interface. The reduction in the VT upon LP incorporation can be attributed to the additional ionic contribution of ClO4- to the EDL along with the trap density (NT) reduction at dielectric/OS interface.

Micro/Nano-Fabrication of Flexible Poly(3,4-Ethylenedioxythiophene)-Based Conductive Films for High-Performance Microdevices.

With the increasing demands for novel flexible organic electronic devices, conductive polymers are now becoming the rising star for reaching such targets, which has witnessed significant breakthroughs in the fields of thermoelectric devices, solar cells, sensors, and hydrogels during the past decade due to their outstanding conductivity, solution-processing ability, as well as tailorability. However, the commercialization of those devices still lags markedly behind the corresponding research advances, arising from the not high enough performance and limited manufacturing techniques. The conductivity and micro/nano-structure of conductive polymer films are two critical factors for achieving high-performance microdevices. In this review, the state-of-the-art technologies for developing organic devices by using conductive polymers are comprehensively summarized, which will begin with a description of the commonly used synthesis methods and mechanisms for conductive polymers. Next, the current techniques for the fabrication of conductive polymer films will be proffered and discussed. Subsequently, approaches for tailoring the nanostructures and microstructures of conductive polymer films are summarized and discussed. Then, the applications of micro/nano-fabricated conductive films-based devices in various fields are given and the role of the micro/nano-structures on the device performances is highlighted. Finally, the perspectives on future directions in this exciting field are presented.

“Grafting from” Enabled Stretchable and Highly Fluorescent Carbon Quantum Dot–Polyisoprene Elastomers

Achieving polymer nanocomposites with improved elasticity and stable mechanical and fluorescence properties remains challenging due to the aggregation tendency of fluorescent carbon nanomaterials, particularly for a polymer with no functional groups. To alleviate the aforementioned issues, the “grafting from” method can be employed via covalent bonding design. Herein, we exploit the “grafting from” method coupled with reversible fragment-added chain transfer polymerization to construct soft polyisoprene (PI) chains onto a photostable nitrogen, sulfur, and phosphorus-doped carbon quantum dot (NSP–CQD) surface for the preparation of flexible fluorescent NSP–CQDs-grafted-polyisoprene (NSP–CQDs-g-PIx) nanocomposite films. By tuning the molecular weight of PI in NSP–CQDs-g-PIx (x = 8, 13, and 18 kg mol–1), the elastic and mechanical properties can be tailored. Upon an intense tensile cyclic test, the NSP–CQDs-g-PI18K generates remarkable elasticity, indicated by the absence of permanent deformation or residual strain even after multiple loading–unloading tests up to 50 times. Moreover, compared with the blending method that tends to cause reduced photoluminescence properties due to the NSP–CQD agglomeration, the grafting method intelligibly maintains the fluorescence property. This study concludes that “grafting from” is a feasible method for fabricating CQD-loaded composites, which have great potential to meet the demand for advanced stretchable and flexible organic electronic devices.

Aerosol Jet Printed Organic Memristive Microdevices Based on a Chitosan:PANI Composite Conductive Channel

In this study we show a chitosan:polyaniline (CPA)-based ink, responding to eco-biofriendly criteria, specifically developed for the manufacturing of the first organic memristive device (OMD) with an aerosol jet printed conductive channel. Our contribution is in the context of bioelectronics, where there is an increasing interest in emulating neuromorphic functions. In this framework, memristive devices and systems have been shown to be well suited. In particular organic-based devices are envisaged as very promising in some applications, such as brain–machine interfacing, owing to specific properties of organics (e.g., biocompatibility, mixed ionic–electronic conduction). On the other hand, the research activities on flexible organic (bio)electronic devices and direct writing (DW) noncontact techniques increasingly overlap in the effort of achieving reliable applications benefiting from the rapid prototyping to accomplish a fast device optimization. In this context, ink-based techniques, such as aerosol jet printing (AJP), although particularly well suited to implement 3D-printed electronics due to advantages it offers in terms of a wide set of allowed printable materials, still require research efforts aimed at conferring printability to the desired precursors. The developed CPA composite was characterized by FTIR, DLS, and MALDI-TOF techniques, while the related aerosol jet printed films were studied by SEM and profilometry. Taking advantage of the intrinsic and stable electrical conductivity of CPA films, which do not necessarily require any acidic treatment to promote a sustained charge carrier conduction, 10 μm short-channel OMDs were hence manufactured by interfacing the printed CPA layers with a solid polyelectrolyte (SPE). We accordingly demonstrated prototypes of stable and best performing OMD devices with downscaled features, showing well-defined counterclockwise hysteresis/rectification and an enhanced durability. These properties pave the way to further improving performance, as well as to realizing a direct integration of the devices into hardware neural networks by in-line fabrication routes.

On-the-Fly Short-Pulse R2R Laser Patterning Processes for the Manufacturing of Fully Printed Semitransparent Organic Photovoltaics.

Ultrafast laser patterning is an essential technology for the low-cost and large area production of flexible Organic Electronic (OE) devices, such as Organic Photovoltaics (OPVs). In order to unleash the potential of ultrafast laser processing to perform the selective and high precision removal of complex multilayers from printed OPV stacks without affecting the underlying nanolayers, it is necessary to optimize its parameters for each nanolayer combination. In this work, we developed an efficient on-the-fly picosecond (ps) laser scribing process (P1, P2 and P3) using single wavelength and single step/pass for the precise and reliable in-line patterning of Roll-to-Roll (R2R) slot-die-coated nanolayers. We have investigated the effect of the key process parameters (pulse energy and overlap) on the patterning quality to obtain high selectivity on the ablation of each individual nanolayer. Finally, we present the implementation of the ultrafast laser patterning process in the manufacturing of fully R2R printed flexible semitransparent OPV modules with a 3.4% power conversion efficiency and 91% Geometric Fill Factor (GFF).

Flexible Organic Electronic Devices for Pulsed Electric Field Therapy of Glioblastoma

Glioblastoma is difficult to eradicate with standard oncology therapies due to its high degree of invasiveness. Bioelectric treatments based on pulsed electric fields (PEFs) are promising for the improvement of treatment efficiency. However, they rely on rigid electrodes that cause acute and chronic damage, especially in soft tissues such as the brain. In this work, flexible electronics were used to deliver PEFs to tumors and the biological response was evaluated with fluorescent microscopy. Interdigitated gold electrodes on a thin, transparent parylene-C substrate were coated with the conducting polymer PEDOT:PSS, resulting in a conformable and biocompatible device. The effects of PEFs on tumors and their microenvironment were examined using various biological models. First, monolayers of glioblastoma cells were cultured on top of the electrodes to investigate phenomena in vitro. As an intermediate step, an in ovo model was developed where engineered tumor spheroids were grafted in the embryonic membrane of a quail. Due to the absence of an immune system, this led to highly vascularized tumors. At this early stage of development, embryos have no immune system, and tumors are not recognized as foreign bodies. Thus, they can develop fast while developing their own vessels from the existing embryo vascular system, which represents a valuable 3D cancer model. Finally, flexible electrode delivery of PEFs was evaluated in a complete organism with a functional immune system, using a syngenic, orthograft (intracranial) mouse model. Tumor spheroids were grafted into the brain of transgenic multi-fluorescent mice prior to the implantation of flexible organic electrode devices. A sealed cranial window enabled multiphoton imaging of the tumor and its microenvironment during treatment with PEFs over a period of several weeks.

Flexible Organic Electronic Devices for Pulsed Electric Field Therapy of Glioblastoma.

Glioblastoma is difficult to eradicate with standard oncology therapies due to its high degree of invasiveness. Bioelectric treatments based on pulsed electric fields (PEFs) are promising for the improvement of treatment efficiency. However, they rely on rigid electrodes that cause acute and chronic damage, especially in soft tissues such as the brain. In this work, flexible electronics were used to deliver PEFs to tumors and the biological response was evaluated with fluorescent microscopy. Interdigitated gold electrodes on a thin, transparent parylene-C substrate were coated with the conducting polymer PEDOT:PSS, resulting in a conformable and biocompatible device. The effects of PEFs on tumors and their microenvironment were examined using various biological models. First, monolayers of glioblastoma cells were cultured on top of the electrodes to investigate phenomena in vitro. As an intermediate step, an in ovo model was developed where engineered tumor spheroids were grafted in the embryonic membrane of a quail. Due to the absence of an immune system, this led to highly vascularized tumors. At this early stage of development, embryos have no immune system, and tumors are not recognized as foreign bodies. Thus, they can develop fast while developing their own vessels from the existing embryo vascular system, which represents a valuable 3D cancer model. Finally, flexible electrode delivery of PEFs was evaluated in a complete organism with a functional immune system, using a syngenic, orthograft (intracranial) mouse model. Tumor spheroids were grafted into the brain of transgenic multi-fluorescent mice prior to the implantation of flexible organic electrode devices. A sealed cranial window enabled multiphoton imaging of the tumor and its microenvironment during treatment with PEFs over a period of several weeks.

Mechanical Fatigue Resistance of Polydiketopyrrolo‐Pyrrole‐Dithienylthieno[3,2‐b]thiophene‐Based Flexible Field‐Effect Transistors

AbstractMechanical durability is one of the main obstacles of flexible organic electronic devices. In this work, the fatigue behavior of flexible field‐effect transistors based on a diketopyrrolo‐pyrrole‐dithienylthieno[3,2‐b]thiophene polymer is reported. An especially for that purpose designed bending setup allows to perform precise multiple deformation cycles of the transistor channel area while monitoring the device behavior. The transistors show high operational stability upon 100 bending cycles at a radius of 500 µm. Bending at smaller radius of 100 µm leaves the functionality of the parylene dielectric intact but induces serious mechanical fractures in the semiconducting film. Despite macroscopic defects, the transistors still reveal good reliability including high charge carrier mobility, due to presence of sufficient pathways for the charge carrier transport and to a low gate leakage. It is also observed that thinner polymer films are more sensitive to the deformation‐induced defects leading to a larger decrease in device performance, especially during the initial bending cycles. In thicker DPP‐DTT films, the crack propagation less affects the semiconductor/dielectric interface, at which the main charge carrier transport take place, resulting in a more stable device operation. Therefore, the work provides fundamental understanding of the fatigue behavior of flexible transistors based on semiconducting polymers.

The effect of ethylene glycol post-treatment on the electrical conductivity of PEDOT: PSS thin films

The application of organic conducting polymers such as poly (3,4-ethylene dioxythiophene): poly (4-styrene sulfonate) (PEDOT: PSS) is vastly expanding for the development of advanced and flexible organic electronic devices, such as solar cells, light-emitting diodes, and organic electrochemical transistors (OECTs). Also, PEDOT: PSS can perfectly replace high-cost Indium tin oxide (ITO) thin films. In this study, PEDOT: PSS was synthesized via the chemical oxidative polymerization method. The film formation was carried out through a feasible drop-casting method onto a cleaned glass substrate. To further enhance the conductivity of pristine PEDOT: PSS, the PEDOT: PSS thin films were post-treated with different concentrations (3, 5, and 7% v/v) of ethylene glycol (EG). Based on the electrochemical impedance spectroscopy (EIS) analysis, it was revealed that the post-treated sample had a higher conductivity value compared to the untreated sample (2.48 × 10-4 S/cm), with the highest recorded conductivity value of 2.67 ×10-3 S/cm at 5% v/v of EG. This result corresponds to the previous study, which highlighted that the optimum concentration of EG is 5% v/v to achieve the optimum conductivity value for thin film application. Furthermore, the structural properties of the thin films were characterized using Fourier transform infrared (FTIR) spectroscopy to confirm the presence of PEDOT: PSS and EG in the samples.

High-k Fluoropolymers Dielectrics for Low-Bias Ambipolar Organic Light Emitting Transistors (OLETs).

Organic light emitting transistors (OLETs) combine, in the same device, the function of an electrical switch with the capability of generating light under appropriate bias conditions. In this work, we demonstrate how engineering the dielectric layer based on high-k polyvinylidene fluoride (PVDF)-based polymers can lead to a drastic reduction of device driving voltages and the improvement of its optoelectronic properties. We first investigated the morphology and the dielectric response of these polymer dielectrics in terms of polymer (P(VDF-TrFE) and P(VDF-TrFE-CFE)) and solvent content (cyclopentanone, methylethylketone). Implementing these high-k PVDF-based dielectrics enabled low-bias ambipolar organic light emitting transistors, with reduced threshold voltages (<20 V) and enhanced light output (compared to conventional polymer reference), along with an overall improvement of the device efficiency. Further, we preliminary transferred these fluorinated high-k dielectric films onto a plastic substrate to enable flexible light emitting transistors. These findings hold potential for broader exploitation of the OLET platform, where the device can now be driven by commercially available electronics, thus enabling flexible low-bias organic electronic devices.

Strategies for the Development of Conjugated Polymer Molecular Dynamics Force Fields Validated with Neutron and X-ray Scattering.

Conjugated polymers (CPs) enable a wide range of lightweight, lower cost, and flexible organic electronic devices, but a thorough understanding of relationships between molecular structure and dynamics and electronic performance is critical for improved device efficiencies and for new technologies. Molecular dynamics (MD) simulations offer in silico insight into this relationship, but their accuracy relies on the approach used to develop the model's parameters or force field (FF). In this Perspective, we first review current FFs for CPs and find that most of the models implement an arduous reparameterization of inter-ring torsion potentials and partial charges of classical FFs. However, there are few FFs outside of simple CP molecules, e.g., polythiophenes, that have been developed over the last two decades. There is also limited reparameterization of other parameters, such as nonbonded Lennard-Jones interactions, which we find to be directly influenced by conjugation in these materials. We further provide a discussion on experimental validation of MD FFs, with emphasis on neutron and X-ray scattering. We define multiple ways in which various scattering methods can be directly compared to results of MD simulations, providing a powerful experimental validation metric of local structure and dynamics at relevant length and time scales to charge transport mechanisms in CPs. Finally, we offer a perspective on the use of neutron scattering with machine learning to enable high-throughput parametrization of accurate and experimentally validated CP FFs enabled not only by the ongoing advancements in computational chemistry, data science, and high-performance computing but also using oligomers as proxies for longer polymer chains during FF development.

Assessing the Donor–Acceptor Nature and the Electrochemical Stability of a Fluorene–Diketopyrrolopyrrole–Thiophene-Based Copolymer

Organic dyes have been studied for applications in large-area, flexible, cheap, and efficient organic electronic devices. Among them, diketopyrrolopyrrole (DPP) has gained attention thanks to its planar structure, photochemical and thermal stability, and easy processability. Also, the electron-withdrawing nature of DPP makes its application attractive in the synthesis of donor–acceptor (D–A) copolymers, with appealing features such as the tunable energy levels and photophysical and electrochemical properties. Inspired by these exciting characteristics, a copolymer was developed based on DPP, thiophene, and fluorene (PFDPP2T). Photophysical and electrochemical studies using both experimental and theoretical approaches were performed aiming to understand the properties of this material, such as, for instance, the D–A characteristic and the outstanding electrochemical stability upon oxidation that enables more than 400 cycles of p-doping. The outcomes unveil fundamental aspects of this class of copolymers, reinforcing their suitability for photo-electrochemical and optoelectronic applications.

Polymer-Laminated Ti3C2TX MXene Electrodes for Transparent and Flexible Field-Driven Electronics.

MXenes (Ti3C2TX) are two-dimensional transition-metal carbides and carbonitrides with high conductivity and optical transparency. However, transparent MXene electrodes with high environmental stability suitable for various flexible organic electronic devices have rarely been demonstrated. By laminating a thin polymer film onto a solution-processed MXene layer to protect the MXene film from harsh environmental conditions, we present transparent and flexible MXene electronic devices. A thin polymer layer spin-coated onto a transparent MXene electrode provides environmental stability even under air exposure longer than 7 d at high temperatures (up to 70 °C) and humidity levels (up to 50%) without degrading the transparency of the electrode. The resulting polymer-laminated (PL) MXene electrode facilitates the development of a variety of field-driven photoelectronic devices by exploiting the electric field exerted between the MXene layer and the counter electrode through the insulating polymer. Field-induced electroluminescent displays, based on both organic and inorganic phosphors, with PL-MXene electrodes are demonstrated with high transparency and mechanical flexibility. Furthermore, our PL-MXene electrode exhibits high versatility through successful implementation in capacitive-type pressure sensors and triboelectric nanogenerators, resulting in field-driven sensing and energy harvesting electronic devices with excellent operation reliability.

Delamination and Wrinkling of Flexible Conductive Polymer Thin Films

AbstractPolymer based conductive and transparent thin films are an important class of functional materials at the heart of flexible organic electronic devices. These flexible films are prone to degradation and to mechanical instability leading to the formation of blisters, wrinkles, and cracks. This is detrimental to their use especially in the case of multilayer devices. Here, it is shown that a simple water or solvent drop deposited on such films gives rise to a buckling instability and the formation of several folds due to the tendency of these films to swell in contact with the solvent. A phase diagram of the instability portraying its domain of existence, and thus the means to inhibit it, is proposed. By depositing drops on such films and observing the instability, material parameters such as the elastic modulus of the thin films or their energy of adhesion to the substrate can be estimated reliably. Further, the instability can be harnessed to pattern surfaces at low cost giving rise to percolated and more conductive pathways in the conductive polymer films under scrutiny.

Investigation of electronic properties of chemical vapor deposition grown single layer graphene via doping of thin transparent conductive films.

It is a crucial challenge to obtain the desired electronic properties of two-dimensional materials for various ubiquitous applications and improvements in the existing technology. In this article, we have demonstrated the modulation in electronic features of the chemical vapor deposition (CVD) grown single-layer graphene (SLG) via wet doping of poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The PEDOT:PSS is well known as conducting polymer and used as transparent conducting electrode in flexible organic electronic devices. The effect of doping on SLG samples were examined by Raman spectroscopy, electrical transport measurement, atomic force microscopy (AFM), and Kelvin probe force microscopy (KPFM). The Raman peaks position of doped samples provided sought evidence of p-type doping of SLG after the deposition of PEDOT:PSS films. The electrical measurement confirmed the p-type doping of SLG and also revealed enhanced carrier density and mobility of SLG after the deposition of PEDOT:PSS films. AFM micrographs revealed the homogeneous loading of PEDOT:PSS particles over the SLGs. Further, KPFM technique was used to estimate the work function modulation of SLG after PEDOT:PSS film deposition. Our investigation will be useful for understanding the device physics as well as improvement of photovoltaic devices based on PEDOT:PSS coated graphene.

Super Gas Barrier of a Polyelectrolyte/Clay Coacervate Thin Film.

Transparent polymeric thin films with high oxygen barrier are important for extending the shelf life of food and protecting flexible organic electronic devices. Polyelectrolyte/clay multilayer nanocoatings are shown to exhibit super gas barrier performance, but the layer-by-layer assembly process requires numerous deposition steps. In an effort to more quickly fabricate this type of barrier, a polyelectrolyte/clay coacervate composed of branched polyethyleneimine (PEI), poly(acrylic acid) (PAA), and kaolinite (KAO) clay is prepared and deposited in a single step, followed by humidity and thermal post-treatments. When deposited onto a 179 µm poly(ethylene terephthalate) (PET) film, a 4 µm coacervate coating reduces the oxygen transmission rate (OTR) by more than three orders of magnitude, while maintaining high transparency. This single-step deposition process uses only low-cost, water-based components and ambient conditions, which can be used to for sensitive food and electronics packaging.

(Invited) Atomic Layer Deposition of Functional Films for Organic Optoelectronic Devices

Among the advanced electronic devices, transparent flexible organic electronic devices with rapid development are the most promising technologies to customers and industries. However, thin film encapsulation (TFE) and transparent oxide conductive (TOC) of organic devices still remain a big challenge, because of the difficulty in low temperature and low plasma power fabricating process. Atomic layer deposition (ALD) is increasingly used in the field of organic electronics. However, the deposition of ALD outside the temperature window still cannot be stably implemented. In this study, transient steric hindrance caused by gas-phase molecules at low-temperature (80℃) was investigated. In order to mitigate the effect of this transient hindrance, a process of consecutive short-pulses was adopted in fabricating TFE and TOC. Overall, the proposed idea would help low temperature ALD for organic electronics become mature and be widely promoted.

The development of conjugated polymers as the cornerstone of organic electronics

The expansion of the field of organic electronics has hinged upon structural and fundamental developments in the field of conjugated polymers. Conjugated polymers allow for the manufacture of low-cost, light-weight, flexible organic electronic devices, with notable applications in organic photovoltaics (OPV), organic field effect transistors (OFET), and organic light emitting diodes (OLED). This extraordinary breadth of applications is due to the remarkable diversity of structure, an extensive understanding of structure-function relationships, and the relative ease of structural tuning. Important advancements and the development of such applications is largely due to the evolution of polymer structure, enabled by a broad range of synthetic methods for the tailoring of structures and the development of improved polymerization conditions to limit defects. This perspective provides background from the early days of concerted and focused conjugated polymer research (1970s-1990) to the present, and describes how the tailoring of conjugated polymer structure has now become closely tied to application. A significant focus is also directed to how polymerization methods have evolved from the aggressive, unselective conditions used for oxidative polymerizations to finely tuned transition-metal catalyzed polymerizations that can provide incredibly high structural-fidelity and can proceed through C–H activation. Areas for future work and emerging areas are also discussed, such as high-performing polymers without added structural and synthetic complexity, identifying polymer structures with improved environmental stability, flexible and transient or bioresorbable conjugated polymers, mixed-ion conductors, and photocatalytic and select biological applications.