Dependence of the solar cell performance on nanocarbon/Si heterojunctions

Solar cells that combine single-crystalline silicon （Si） with graphene （G） have been widely researched in order to develop next-generation photovoltaic devices. However, the power conversion efficiency （PCE） of G/Si solar cell without chemical doping is commonly low due to the relatively high resistance of graphene. In this work, through combining graphene with carbon nanotube （CNT） networks, we fabricated three kinds of hybrid nanocarbon film/Si heterojunction solar cells in order to increase the PCE of the graphene based Si solar cell. We investigated the characteristics of different nanocarbon film/Si solar cells and found that their performance depends on the heterojunctions. Specifically, a doping-free G-CNT/Si solar cell demonstrated a high PCE of 7.9%, which is nearly equal to the combined value of two individuals （G/Si and CNT/Si）. This high efficiency is attributed to the synergistic effect of graphene and CNTs, and can be further increased to 9.1% after applying a PMMA antireflection coating. This study provides a potential way to further improve the Si based heterojunction solar cells.

Electromechanical actuation of CNT/PVDF composite films based on a bridge configuration

Bridged strips consisting of carbon nanotubes and poly（vinylidene fluoride） are developed, which exhibit notable deflection in response to very low driven voltages（ 1 V）, because of both the excellent conductivity of the unique carbon nanotube film and the powerful thermal expansion capability of the polymer. The actuators demonstrate periodic vibrations motivated by the alternating signals. The amplitude of displacement is dependent not only on the driven voltage but also on the applied frequency. The mechanism of actuation is confirmed to be the thermal power induced by the electrical heating. By accelerating the dissipation of heat, the vibration response at higher frequencies can be significantly enhanced.The useful locomotion shows great promise in potential applications such as miniature smart devices and micro power generators.

Free-standing,curled and partially reduced graphene oxide network as sulfur host for high-performance lithium–sulfur batteries

Lithium–sulfur（Li–S） batteries have received more and more attention because of higher specific capacity and energy density of sulfur than current lithium–ion batteries. However, the low electrical conductivity of sulfur and its discharge product, and also the high dissolution of polysulfides restrict the Li–S battery practical applications. To improve their performances, in this work, we fabricate a novel free-standing, curled and partially reduced graphene oxide（CPrGO for short） network and combine it with sulfur to form a CPrGO–S composite as a cathode for Li–S battery. With sulfur content of 60 wt%, the free-standing CPrGO–S composite network delievers an initial capacity of 988.9 m Ah·g^（-1）. After 200 cycles,it shows a stable capacity of 841.4 m Ah·g^（-1） at 0.2 C, retaining about 85% of the initial value. The high electrochemical performance demonstrates that the CPrGO–S network has great potential applications in energy storage system. Such improved properties can be ascribed to the unique free-standing and continous CPrGO–S network which has high specific surface area and good electrical conductivity. In addition, oxygen-containing groups on the partially reduced graphene oxide are beneficial to preventing the polysulfides from dissolving into electrolyte and can mitigate the ＂shuttle effect＂.

Highly conductive and transparent carbon nanotube-based electrodes for ultrathin and stretchable organic solar cells

In this work, we have presented a freestanding and flexible CNT-based film with sheet resistance of 60 ？/ and transmittance of 82% treated by nitric acid and chloroauric acid in sequence. Based on modified CNT film as a transparent electrode, we have demonstrated an ultrathin, flexible organic solar cell（OSC） fabricated on 2.5-μm PET substrate. The efficiency of OSC, combined with a composite film of poly（3-hexylthiophene）（P3HT） and phenyl-C61 butyric acid methyl ester（PCBM） as an active layer and with a thin layer of methanol soluble biuret inserted between the photoactive layer and the cathode, can be up to 2.74% which is approximate to that of the reference solar cell fabricated with ITO-coated glass（2.93%）. Incorporating the as-fabricated ITO-free OSC with pre-stretched elastomer, 50% compressive deformation can apply to the solar cells. The results show that the as-prepared CNT-based hybrid film with outstanding electrical and optical properties could serve as a promising transparent electrode for low cost, flexible and stretchable OSCs, which will broaden the applications of OSC and generate more solar power than it now does.