Solution-processed organic photovoltaic cells (OPVs) hold great promise to enable roll-to-roll printing of environmentally friendly, mechanically flexible and cost-effective photovoltaic devices. Nevertheless, many high-performing systems show best power conversion efficiencies (PCEs) with a thin active layer (thickness is ~100 nm) that is difficult to translate to roll-to-roll processing with high reproducibility. Here we report a new molecular donor, benzodithiophene terthiophene rhodanine (BTR), which exhibits good processability, nematic liquid crystalline behaviour and excellent optoelectronic properties. A maximum PCE of 9.3% is achieved under AM 1.5G solar irradiation, with fill factor reaching 77%, rarely achieved in solution-processed OPVs. Particularly promising is the fact that BTR-based devices with active layer thicknesses up to 400 nm can still afford high fill factor of ~70% and high PCE of ~8%. Together, the results suggest, with better device architectures for longer device lifetime, BTR is an ideal candidate for mass production of OPVs.

Wearable dry electrodes are needed for long-term biopotential recordings but are limited by their imperfect compliance with the skin, especially during body movements and sweat secretions, resulting in high interfacial impedance and motion artifacts. Herein, we report an intrinsically conductive polymer dry electrode with excellent self-adhesiveness, stretchability, and conductivity. It shows much lower skin-contact impedance and noise in static and dynamic measurement than the current dry electrodes and standard gel electrodes, enabling to acquire high-quality electrocardiogram (ECG), electromyogram (EMG) and electroencephalogram (EEG) signals in various conditions such as dry and wet skin and during body movement. Hence, this dry electrode can be used for long-term healthcare monitoring in complex daily conditions. We further investigated the capabilities of this electrode in a clinical setting and realized its ability to detect the arrhythmia features of atrial fibrillation accurately, and quantify muscle activity during deep tendon reflex testing and contraction against resistance.

The conductivity of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films was significantly enhanced by preferential solvations of the hydrophobic PEDOT and hydrophilic PSS chains with cosolvents. When a PEDOT:PSS film prepared from the PEDOT:PSS aqueous solution was treated with water or a common organic solvent like ethanol, iso-propyl alcohol (IPA), acetonitrile (ACN), acetone, or tetrahydrofuran (THF), its conductivity did not change remarkably. But the conductivity was significantly enhanced when the PEDOT:PSS film was treated with a cosolvent of water and one of these common organic solvents. The conductivity enhancement was affected by several factors, including the ratio of the organic solvent to water, the dielectric constant of the organic solvent, and the temperature during the treatment. The conductivity enhancement from 0.2 S cm⁻¹ to 103 S cm⁻¹ was observed. The significant conductivity enhancement is attributed to the preferential solvation of PEDOT:PSS with a cosolvent. Water and the organic solvent of the cosolvent preferentially solvate the hydrophilic PSS and hydrophobic PEDOT chains, respectively. The preferential solvation of a PEDOT:PSS film with a cosolvent induces the phase separation of the insulator PSSH chains from the PEDOT:PSS film, aggregation of PSSH segments in the PEDOT:PSS film, and the conformational change of the PEDOT chains from coiled to linear. The cosolvent-treated PEDOT:PSS films were quite smooth and could be used to replace indium tin oxide (ITO) as the transparent electrode of electronic devices. Polymer photovoltaic cells (PVs) with the cosolvent-treated PEDOT:PSS films as the transparent electrode exhibited high photovoltaic performance.