Heteroatom doped porous carbon flakes were prepared via carbonization of Chinese human hair fibers and employed for high-performance supercapacitor electrode materials. The morphology and chemical composition of the resultant carbon materials were characterized by electron microscopy (EM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) measurements. Human hair carbonized at 800 °C exhibited high charge storage capacity with a specific capacitance of 340 F g⁻¹ in 6 M KOH at a current density of 1 A g⁻¹ and good stability over 20 000 cycles. The specific capacitance of 126 F g⁻¹ is also verified in a 1 M LiPF₆ ethylene carbonate/diethyl carbonate (EC/DEC) organic electrolyte at a current density of 1 A g⁻¹. The high supercapacitor performance could be due to the micro/mesoporosity combined with high effective surface area and heteroatom doping effects, combining double layer and Faradaic contributions.

Fully integrated ultrathin, transparent and foldable energy storage devices are essential for the development of smart wearable electronics, yet typical supercapacitor electrodes are substrate-supported which limits their thickness, transparency and mechanical properties. Employing freestanding transparent electrodes with no substrate support could bring ultrathin, foldable and designable supercapacitors closer to reality. Herein, we report a freestanding, ultrathin (<5 μm), highly conductive (3 × 10⁴ S cm⁻¹), highly transparent (>84% transmittance) and foldable metallic network electrode, loaded with MnO₂ by electrochemical deposition, as a supercapacitor electrode. The freestanding metallic network electrode is fabricated via a simple and low-cost laser direct-writing micro-patterning technique followed by a selective electrodeposition process, where the metallic network patterns, network periods, metal thickness and also the electrode film patterns can be designed for different applications. The obtained freestanding MnO₂@Ni network electrode delivers an outstanding areal capacitance of 80.7 mF cm⁻² and long-term performance stability (96.3% after 10 000 cycles). Moreover, the symmetric solid-state supercapacitors employing the freestanding MnO₂@Ni network electrode not only show high areal capacitance as well as high optical transparency (>80% transmittance), but also can be tailored, attached, folded, rolled up, and crumpled into any object or various shapes with only slight performance degradation. The advent of such freestanding transparent metallic network electrodes may open up a new avenue for realizing fully integrated ultrathin, foldable and designable supercapacitors towards self-powered wearable electronics.

Contact-metal dependent current injection in top-contact pentacene thin-film transistors is analyzed, and the local mobility in the contact region was found to follow the Meyer-Neldel rule. An exponential trap distribution, rather than the metal/organic hole injection barrier, is proposed to be the dominant factor of the contact resistance in pentacene thin-film transistors. The variable temperature measurements revealed a much narrower trap distribution in the copper contact compared with the corresponding gold contact, and this is the origin of the smaller contact resistance for copper despite a lower work function.