The redox-diffusion (RD) battery concept introduces an environmentally friendly solution for stretchable batteries in autonomous wearable electronics. By utilising plant-based redox-active biomolecules and cellulose fibers for the electrode scaffold, separator membrane, and current collector, along with a biodegradable elastomer encapsulation, the battery design overcomes the reliance on unsustainable transition metal-based active materials and non-biodegradable elastomers used in existing stretchable batteries. Importantly, it addresses the drawback of limited attainable battery capacity, where increasing the active material loading often leads to thicker and stiffer electrodes with poor mechanical properties. The concept decouples the active material loading from the mechanical structure of the electrode, enabling high mass loadings, while retaining a skin-like young's modulus and stretchability. A stretchable ion-selective membrane facilitates the RD process, allowing two separate redox couples, while preventing crossovers. This results in a high-capacity battery cell that is both electrochemically and mechanically stable, engineered from sustainable plant-based materials. Notably, the battery components are biodegradable at the end of their life, addressing concerns of e-waste and resource depletion. A stretchable battery design that uses sustainable plant-based materials and enables high electrochemical and mechanical performance and is biodegradable at the end-of-life.

Next-generation wearables will interface intimately with the human body either on-skin, implanted or woven into clothing. This requires electrical components that match the mechanical properties of biological tissues - stretchability (up to 60% strain) and softness (Youngs modulus of similar to 1 kPa to 1 MPa). As wearables become increasingly complex, the energy and mechanical requirements will increase, and an integrated power supply unit such as a soft and stretchable battery is needed to achieve autonomy and wireless operation. However, two key challenges remain for current stretchable battery technology: the mechanical performance (softness and stretchability) and its relation to the size and charge storage capacity (challenge I), and the sustainability and biocompatibility of the battery materials and its components (challenge II). Integrating all these factors into the battery design often leads to a trade-off between the various properties. This perspective will evaluate current strategies for achieving sustainable stretchable batteries and provide a discussion on possible avenues for future research. Stretchable battery technology still faces several challenges to progress the development of next-generation wearables. This perspective will evaluate current strategies and provide a discussion on possible avenues for future research.

A wide range of nanophotonic applications rely on polarization-dependent plasmonic resonances, which usually requires metallic nanostructures that have anisotropic shape. This work demonstrates polarization-dependent plasmonic resonances instead by breaking symmetry via material permittivity. The study shows that molecular alignment of a conducting polymer can lead to a material with polarization-dependent plasma frequency and corresponding in-plane hyperbolic permittivity region. This result is not expected based only on anisotropic charge mobility but implies that also the effective mass of the charge carriers becomes anisotropic upon polymer alignment. This unique feature is used to demonstrate circularly symmetric nanoantennas that provide different plasmonic resonances parallel and perpendicular to the alignment direction. The nanoantennas are further tuneable via the redox state of the polymer. Importantly, polymer alignment could blueshift the plasma wavelength and resonances by several hundreds of nanometers, forming a novel approach toward reaching the ultimate goal of redox-tunable conducting polymer nanoantennas for visible light. Traditional anisotropic nanoantennas have asymmetric shape. In this work, symmetry is instead broken by straining of a conducting polymer, leading to an in-plane anisotropic plasma frequency. This enables circularly symmetric nanoantennas with polarization-dependent localized surface plasmon resonances. The polarization dependence is consistent with inverse changes of the effective mass and mobility of thecharge carriers along different in-plane directions.image

Conducting polymers (CPs) constitute a promising building block to establish next-generation stretchable electronics. However, achieving CPs with both high electrical conductivity and outstanding mechanical stretchability beyond flexibility is still a major challenge. Therefore, understanding the key factors controlling such characteristics of CPs is required. Herein, a method to simultaneously manipulate the mechanical and electrical properties of a representative CP, PEDOT:PSS, by modifying ionic liquid (IL) additives is reported. The cation/anion modification of ILs distinctly improves the electrical conductivity of PEDOT:PSS up to ≈1075 S cm−1, and the PEDOT:PSS/IL films showing higher conductivity also exhibit superior electromechanical stretchability, enabling them to maintain their initial conductivity under a tensile strain of 80%. Based on grazing incidence wide angle X-ray scattering and Fourier transform infrared spectroscopy analyses, it is found that the cation/anion-modified ILs control the crystallinity and π–π stacking density of conjugated PEDOT chains and the growth of amorphous PSS domains via IL-induced phase separation between PEDOT and PSS, which can be the origin of the significant conductivity and stretchability improvements in PEDOT:PSS/IL composites. This study provides guidance to develop highly stretchable CP-based conductors/electrodes.

The tailoring of the chromaticity of white organic light-emitting diodes (WOLEDs) has presented a significant challenge in their application in smart lighting sources to improve the quality of life and human performance. Here, a new microcavity WOLED (M-WOLED) structure to modulate the chromaticity of the emitted light is demonstrated by only adjusting the thickness of the white light-emitting layer. By introducing a polymer-metal hybrid electrode that functions both as a partially reflective mirror and a transparent electrode, a very simple microcavity architecture that does not require additional outer mirrors, such as distributed Bragg reflectors is developed. The resulting M-WOLEDs exhibit reddish-, greenish-, and bluish-white colors with different thicknesses of the single white light-emitting layer.

In this chapter, the authors summarize their understanding of Poly(3,4-ethylenedioxythiophene) (PEDOT), with respect to its chemical and physical fundamentals. They focus upon the structure of several PEDOT systems, from the angstrom level and up, and the impact on both electronic and ionic transport. The authors discuss the structural properties of PEDOT:X and PEDOT:poly(styrenesulfonate) based on experimental data probed at the scale ranging from angstrom to submicrometer. The morphology of PEDOT is influenced by the nature of counter-ions, especially at high oxidation levels. The doping anions intercalate between PEDOT chains to form a “sandwich” structure to screen the positive charges in PEDOT chains. The authors provide the main transport coefficients such as electrical conductivity s, Seebeck coefficient S, and Peltier coefficient σ, starting from a general thermodynamic consideration. The optical conductivity of PEDOT has also been examined based on the effective medium approximation, which is normally used to describe microscopic permittivity properties of composites made from several different constituents.

Despite the high expectation of deformable and see-through displays for future ubiquitous society, current light-emitting diodes (LEDs) fail to meet the desired mechanical and optical properties, mainly because of the fragile transparent conducting oxides and opaque metal electrodes. Here, by introducing a highly conductive nanofibrillated conducting polymer (CP) as both deformable transparent anode and cathode, ultraflexible and see-through polymer LEDs (PLEDs) are demonstrated. The CP-based PLEDs exhibit outstanding dual-side light-outcoupling performance with a high optical transmittance of 75% at a wavelength of 550 nm and with an excellent mechanical durability of 9% bending strain. Moreover, the CP-based PLEDs fabricated on 4 µm thick plastic foils with all-solution processing have extremely deformable and foldable light-emitting functionality. This approach is expected to open a new avenue for developing wearable and attachable transparent displays.