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High electrochemical performance energy storage devices coupled with low cost and high safety operation are in urgent need due to the increasing demand for flexible and wearable electronics. For these applications lithium-ion and sodium-ion batteries are vastly limited due to their relatively low power density and security risks. On the other hand, conventional supercapacitors are suitable for flexible and wearable electronics due to their high power density while their low energy density has hindered their wide applications. Lithium or sodium ion hybrid supercapacitors are promising energy storage devices that benefit from the combined high energy density of batteries and high power density of supercapacitors. However, the use of organic electrolytes and shortage of lithium resources are expected to limit their widespread commercialization for flexible and wearable electronics. Here, for the first time, we introduce a safe and flexible solid-state zinc ion hybrid supercapacitor (ZHS) based on co-polymer derived hollow carbon spheres (HCSs) as the cathode, polyacrylamide (PAM) hydrogel as the electrolyte and Zn deposited on carbon cloth as the anode. Owing to the high surface area of the HCSs and the hollow structure which improves the ion adsorption and desorption kinetics of the cathode, the flexible solid-state ZHS delivers a highest capacity of 86.8 mA h g−1 and a maximum energy density of 59.7 W h kg−1 with a power density of 447.8 W kg−1. Besides, it displays excellent cycling stability with 98% capacity retention over 15 000 cycles at a current density of 1.0 A g−1. Moreover, the solid-state ZHS is flexible enough to sustain various deformations including squeezing, twisting and folding due to the use of flexible electrodes and electrolytes. Our study unveils a pioneering flexible solid-state ZHS with high safety, which is a promising candidate for flexible and wearable energy storage devices.

Flexible supercapacitors with high areal capacitance are a promising approach for wearable energy-storage technology due to the limitation of the surface area of the human body (about 2 m2). Meanwhile, a tolerance to deformation and mechanic damage is critical for wearable applications. However, it is still a challenge to achieve supercapacitors with outstanding electrochemical performance and wearability, simultaneously. To solve this problem, we report high-performance, flexible, and tailorable solid-state supercapacitors enabled by Co3O4@PPy nanorod bundle arrays immobilized on carbon fiber cloth (CFC). Furthermore, a solid-state asymmetric supercapacitor was assembled using a freestanding Co3O4@PPy electrode, a freestanding porous carbon electrode, and PVA gel electrolyte. Benefiting from a 3D structure and the synergetic contribution of the Co3O4 nanorods and electrically conductive PPy layer, the Co3O4@PPy electrode and our developed supercapacitor exhibit a high areal capacitance of 6.67 F cm−2 at a current density of 2 mA cm−2, and 2.47 F cm−2 at 4 mA cm−2, respectively, as well as excellent rate capability. More importantly, the solid-state supercapacitor can be tailored into several units and various shapes. Each unit retains its original electrochemical performance. This work provides a new route to wearable energy-storage technology.

In this paper, systematic investigations on the fabrication and characterization of high performance TiO2 nanorod array perovskite solar cells (NAPSCs) are reported. The TiO2 nanorods, of length around 350–400 nm, were grown by solvothermal technique directly on glass/FTO substrates. From the scanning transmission electron microscopy (STEM) we demonstrate that excellent crystallinity for the TiO2 nanorods can be produced using the solvothermal technique. Precursor consisting of a mixture of PbI2, CH3NH3I (MAI) and CH3NH3Cl (MACl) was used for the growth of perovskite thin films on the glass/FTO/TiO2 nanorod array (TiO2-NA) substrates. It is found that the morphology and quality of the perovskite layer depend strongly on the concentration of MACl in the precursor. Experimental studies on femtosecond transient absorption (fs-TA) indicate that the incorporation of TiO2-NA greatly enhances the collection efficiency of the photo-generated carriers due to substantial increase of interfacial area between the perovskite and TiO2-NA, leading to a reduction in carrier diffusion distance. It is shown to be the key factor that the proposed technique facilitates the use of a thicker perovskite absorber layer (∼500 nm) without compromising on the series resistance. Detailed J–V characterization shows that the NAPSCs exhibit negligible hysteresis with a power conversion efficiency (PCE) >19% for the champion device.

A novel facile and environmentally friendly strategy was developed to prepare Fe3O4 and graphene (Fe3O4/G) nanocomposites through in situ thermal reduction of FeOOH nanorods and graphene oxide (GO) nanocomposites, in which GO serves as a structural platform to uniformly incorporate as-prepared FeOOH nanorods via mutual electrostatic interactions. In the preparation process, GO was added into a FeOOH solution by two steps which are beneficial to form well confined nanocomposites. As anode materials for lithium ion batteries, the Fe3O4/G nanocomposites exhibited significantly enhanced electrochemical performance with excellent cycling stability and a high reversible capacity of ∼1200 mA h g−1 at a current density of 1000 mA g−1 after long-term testing for 1000 cycles, and a remarkable rate capability of ∼660 mA h g−1 at 5000 mA g−1, thus exhibiting great potential as advanced anode materials for lithium ion batteries.

We develop a one-pot and scalable hydrothermal strategy to prepare nanoscale metallic Cu incorporated CuFe2O4 hexagonal platelets and graphene (Cu–CuFe2O4/G) composites at a low reaction temperature as anode materials for lithium-ion batteries (LIBs). Nanoscale metallic Cu was attached to CuFe2O4 hexagonal platelets and graphene sheets in the composites. Such structural features are responsible for exploiting the respective advantages to improve electrochemical performance. The Cu–CuFe2O4/G composites deliver a high capacity of 672 mA h g−1 after 200 cycles at a current density of 1000 mA g−1, good rate capability and cyclic stability due to the synergistic effect among CuFe2O4 hexagonal platelets, metallic Cu, and graphene sheets.

Traditionally, lattice-matched substrates are a requisite for the epitaxial growth of one-dimensional (1D) semiconductor nanostructure arrays, while the lack of suitable substrates seriously limits the nanowire (NW) arrays available for future nanoelectronic and nano-optoelectronics applications. In this work, we reported a new strategy for achieving the one-step homoepitaxial growth of highly aligned CdSe NW arrays by utilizing porous silicon as substrates. The porous Si with dense holes could promote the nucleation of CdSe micro-crystals at the early stage of vapor phase transport owing to its high surface energy. Subsequently, the epitaxial growth of CdSe NW arrays would take place on the top surfaces of the micro-crystals, resulting in large-area highly aligned NW arrays. As compared with the conventional epitaxial methods, the hole-induced method is greatly simplified because no lattice-matched substrates or catalysts are needed; furthermore, the universality of the proposed method was demonstrated for a variety of II–VI NW arrays. As a demonstration of the potential applications, preliminary studies on CdSe NW array/Si p–n heterojunction solar cells were shown with an efficiency of ∼0.43% under AM 1.5G illumination.