Solar cells are attractive candidates for clean and renewable power; with miniaturization, they might also serve as integrated power sources for nanoelectronic systems. The use of nanostructures or nanostructured materials represents a general approach to reduce both cost and size and to improve efficiency in photovoltaics. Nanoparticles, nanorods and nanowires have been used to improve charge collection efficiency in polymer-blend and dye-sensitized solar cells, to demonstrate carrier multiplication, and to enable low-temperature processing of photovoltaic devices. Moreover, recent theoretical studies have indicated that coaxial nanowire structures could improve carrier collection and overall efficiency with respect to single-crystal bulk semiconductors of the same materials. However, solar cells based on hybrid nanoarchitectures suffer from relatively low efficiencies and poor stabilities. In addition, previous studies have not yet addressed their use as photovoltaic power elements in nanoelectronics. Here we report the realization of p-type/intrinsic/n-type (p-i-n) coaxial silicon nanowire solar cells. Under one solar equivalent (1-sun) illumination, the p-i-n silicon nanowire elements yield a maximum power output of up to 200 pW per nanowire device and an apparent energy conversion efficiency of up to 3.4 per cent, with stable and improved efficiencies achievable at high-flux illuminations. Furthermore, we show that individual and interconnected silicon nanowire photovoltaic elements can serve as robust power sources to drive functional nanoelectronic sensors and logic gates. These coaxial silicon nanowire photovoltaic elements provide a new nanoscale test bed for studies of photoinduced energy/charge transport and artificial photosynthesis, and might find general usage as elements for powering ultralow-power electronics and diverse nanosystems.

Graphene and related two-dimensional crystals and hybrid systems showcase several key properties that can address emerging energy needs, in particular for the ever growing market of portable and wearable energy conversion and storage devices. Graphene's flexibility, large surface area, and chemical stability, combined with its excellent electrical and thermal conductivity, make it promising as a catalyst in fuel and dye-sensitized solar cells. Chemically functionalized graphene can also improve storage and diffusion of ionic species and electric charge in batteries and supercapacitors. Two-dimensional crystals provide optoelectronic and photocatalytic properties complementing those of graphene, enabling the realization of ultrathin-film photovoltaic devices or systems for hydrogen production. Here, we review the use of graphene and related materials for energy conversion and storage, outlining the roadmap for future applications.

Solar vapour generation is an efficient way of harvesting solar energy for the purification of polluted or saline water. However, water evaporation suffers from either inefficient utilization of solar energy or relies on complex and expensive light-concentration accessories. Here, we demonstrate a hierarchically nanostructured gel (HNG) based on polyvinyl alcohol (PVA) and polypyrrole (PPy) that serves as an independent solar vapour generator. The converted energy can be utilized in situ to power the vaporization of water contained in the molecular meshes of the PVA network, where water evaporation is facilitated by the skeleton of the hydrogel. A floating HNG sample evaporated water with a record high rate of 3.2 kg m h via 94% solar energy from 1 sun irradiation, and 18-23 litres of water per square metre of HNG was delivered daily when purifying brine water. These values were achievable due to the reduced latent heat of water evaporation in the molecular mesh under natural sunlight.

Pressure sensing is an important function of electronic skin devices. The development of pressure sensors that can mimic and surpass the subtle pressure sensing properties of natural skin requires the rational design of materials and devices. Here we present an ultrasensitive resistive pressure sensor based on an elastic, microstructured conducting polymer thin film. The elastic microstructured film is prepared from a polypyrrole hydrogel using a multiphase reaction that produced a hollow-sphere microstructure that endows polypyrrole with structure-derived elasticity and a low effective elastic modulus. The contact area between the microstructured thin film and the electrodes increases with the application of pressure, enabling the device to detect low pressures with ultra-high sensitivity. Our pressure sensor based on an elastic microstructured thin film enables the detection of pressures of less than 1 Pa and exhibits a short response time, good reproducibility, excellent cycling stability and temperature-stable sensing.

Conducting polymer hydrogels represent a unique class of materials that synergizes the advantageous features of hydrogels and organic conductors and have been used in many applications such as bioelectronics and energy storage devices. They are often synthesized by polymerizing conductive polymer monomer within a nonconducting hydrogel matrix, resulting in deterioration of their electrical properties. Here, we report a scalable and versatile synthesis of multifunctional polyaniline (PAni) hydrogel with excellent electronic conductivity and electrochemical properties. With high surface area and three-dimensional porous nanostructures, the PAni hydrogels demonstrated potential as high-performance supercapacitor electrodes with high specific capacitance (∼480 F·g −1 ), unprecedented rate capability, and cycling stability (∼83% capacitance retention after 10,000 cycles). The PAni hydrogels can also function as the active component of glucose oxidase sensors with fast response time (∼0.3 s) and superior sensitivity (∼16.7 μA·mM −1 ). The scalable synthesis and excellent electrode performance of the PAni hydrogel make it an attractive candidate for bioelectronics and future-generation energy storage electrodes.conductive polymer hydrogel | supercapacitors | biosensors H ydrogels are polymeric networks that have a high level of hydration and three-dimensional (3D) microstructures bearing similarities to natural tissues (1, 2). Hydrogels based on conducting polymers [e.g., polythiophene, polyaniline (PAni), and polypyrrole] combine the unique properties of hydrogels with the electrical and optical properties of metals or semiconductors (3-6) thus offering an array of features such as intrinsic 3D microstructured conducting frameworks that promote the transport of charges, ions, and molecules (7). Conducting polymer hydrogels provide an excellent interface between the electronictransporting phase (electrode) and the ionic-transporting phase (electrolyte), between biological and synthetic systems, as well as between soft and hard materials (8). As a result, conducting polymer hydrogels have demonstrated great potential for a broad range of applications from energy storage devices such as biofuel cells and supercapacitors, to molecular and bioelectronics (9) and medical electrodes (8).To date, the synthetic routes toward conducting polymer hydrogels include synthesizing a conducting polymer monomer within a nonconducting hydrogel matrix (8, 9) using multivalent metal ions (Fe 3þ or Mg 2þ ) to crosslink poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) (10, 11) and using nonconducting poly(ethylene glycol) diglycidyl ether, or poly(styrenesulfonate) to crosslink PAni (12, 13); however, nonconducting hydrogel matrix and polymers result in the deterioration of the electrical properties, whereas excessive metal ions may reduce the biocompatibility of hydrogels. Moreover, there have yet been any reports in regard to conductive hydrogels that can be facilely micropatterned, which is important for fabricating hy...