Guifu Zou

Polymer-Embedded Carbon Nanotube Ribbons for Stretchable Conductors

The creation of stretchable electronics is emerging as one of the most interesting research topics in materials science and technology. [ 1,2 ] Devices that are stretchable, foldable, and deformable into complex curvilinear shapes can enable many new applications that would be impossible to achieve by conventional rigid electronics. Examples of such applications range from fl exible displays, electronic eyeball cameras to stretchable electronic implants and conformable skin sensors. [ 3–6 ]

Tailoring the Morphology of Carbon Nanotube Arrays: From Spinnable Forests to Undulating Foams

Directly spinning carbon nanotube (CNT) fibers from vertically aligned CNT arrays is a promising way for the application of CNTs in the field of high-performance materials. However, most of the reported CNT arrays are not spinnable. In this work, by controlling catalyst pretreatment conditions, we demonstrate that the degree of spinnability of CNTs is closely related to the morphology of CNT arrays. Shortest catalyst pretreatment time led to CNT arrays with the best spinnability, while prolonged pretreatment resulted in coarsening of catalyst particles and nonspinnable CNTs. By controlling the coalescence of catalyst particles, we further demonstrate the growth of undulating CNT arrays with uniform and tunable waviness. The CNT arrays can be tuned from well-aligned, spinnable forests to uniformly wavy, foam-like films. To the best of our knowledge, this is the first systematical study on the correlation between catalyst pretreatment, CNT morphology, and CNT spinnability.

Enlarging photovoltaic effect: combination of classic photoelectric and ferroelectric photovoltaic effects

Converting light energy to electrical energy in photovoltaic devices relies on the photogenerated electrons and holes separated by the built-in potential in semiconductors. Photo-excited electrons in metal electrodes are usually not considered in this process. Here, we report an enhanced photovoltaic effect in the ferroelectric lanthanum-modified lead zirconate titanate (PLZT) by using low work function metals as the electrodes. We believe that electrons in the metal with low work function could be photo-emitted into PLZT and form the dominant photocurrent in our devices. Under AM1.5 (100u2005mW/cm2) illumination, the short-circuit current and open-circuit voltage of Mg/PLZT/ITO are about 150 and 2 times of those of Pt/PLZT/ITO, respectively. The photovoltaic response of PLZT capacitor was expanded from ultraviolet to visible spectra, and it may have important impact on design and fabrication of high performance photovoltaic devices based on ferroelectric materials.

Interface engineering toward enhanced efficiency of planar perovskite solar cells

Interface engineering is an efficient method for improving the performance of planar perovskite solar cells (PSCs). In this paper, the performance of PSCs was improved significantly by introducing 4,7-diphenyl-1,10-phenanthroline (Bphen) doped with bis(2-methyldibenzo-[f,h]quinoxaline) (Ir(MDQ)2(acac)) to modify the interface between perovskite (CH3NH3PbI3−xClx)/PCBM (phenyl-C61-butyric acid methyl ester) and an Ag electrode. The power conversion efficiency (PCE) was enhanced up to 15.87%, compared with 10.77% for the reference device without interlayer modification. It was found that the enhanced PCE was attributed to the better interface contact between the perovskite and Ag cathode. A suitable interface roughness is beneficial for reducing the leakage current and the probability of carrier recombination, resulting in an enhanced fill factor and thus improved device efficiency.

Exciton dissociation and photovoltaic effect in germanium nanocrystals and poly(3-hexylthiophene) composites

Exciton dissociation and carrier transport in poly(3-hexylthiophene) (P3HT)/germanium (Ge) nanocrystals composites were investigated by steady-state and time-resolved photoluminescence (PL) as well as photovoltaic (PV) effect. Quenching of the PL quantum yield η and shortening of the PL lifetime τ in the composites were observed, which were ascribed to rapid exciton dissociate at the interface. PV devices were fabricated based on Ge/P3HT composites sandwiched between indium tin oxide and aluminum. The external quantum efficiency spectrum displayed wide photoresponse range, covering both nanocrystals absorption range and P3HT one. Large open circuit voltage up to 0.45 V and obvious short-circuit current were demonstrated in hybrid Ge nanocrystals/P3HT PV device.

Leakage mechanisms of self-assembled (BiFeO3)0.5:(Sm2O3)0.5 nanocomposite films

Nanocomposite (BiFeO3)0.5:(Sm2O3)0.5 films were deposited on (001) oriented Nb-doped SrTiO3 substrates by pulsed laser deposition. The leakage current density versus electric field characteristics were investigated and compared with those of as-deposited and annealed pure BiFeO3 (BFO) thin films. The dominant leakage mechanisms of nanocomposite films were space-charge-limited current and Poole–Frenkle emission for positive and negative biases, respectively. The leakage current density of nanocomposite films was reduced three orders of magnitude in comparison with the as-deposited pure BFO films. The less oxygen vacancies in the BFO phase in the nanocomposite is believed to contribute to the leakage reduction.

Nitrogen-Doped Carbon Dots for “green” Quantum Dot Solar Cells

Considering the environment protection, “green” materials are increasingly explored for photovoltaics. Here, we developed a kind of quantum dots solar cell based on nitrogen-doped carbon dots. The nitrogen-doped carbon dots were prepared by direct pyrolysis of citric acid and ammonia. The nitrogen-doped carbon dots’ excitonic absorption depends on the N-doping content in the carbon dots. The N-doping can be readily modified by the mass ratio of reactants. The constructed “green” nitrogen-doped carbon dots solar cell achieves the best power conversion efficiency of 0.79xa0% under AM 1.5xa0G one full sun illumination, which is the highest efficiency for carbon dot-based solar cells.

Chemical Solution Deposition of Epitaxial Carbide Films

Carbide films exhibit many unique properties. The development of a versatile and simple technique for the deposition of carbide films will enable a wide range of technological applications. Here we report a cost-effective chemical solution deposition or polymer-assisted deposition method for growing epitaxial carbide (including TiC, VC, and TaC) films. These epitaxial carbide films exhibit structural and physical properties similar to the films grown by vapor deposition methods.

Highly Conductive Films of Layered Ternary Transition‐Metal Nitrides

Film studies: Epitaxial films of BaZrN(2) (see TEM image) and BaHfN(2) are grown by polymer-assisted deposition on SrTiO(3) (STO) substrates. The films are phase-pure, allowing the intrinsic physical properties of the ternary nitrides to be studied. From 5 to 300 K, the films exhibit metallic-like resistivity-temperature behavior, with large residual resistivity ratios.

A novel carbon nanotube/polymer composite film for counter electrodes of dye-sensitized solar cells

In the development of optoelectronic and electronic devices, it is critically important, but remains challenging to discover new electrode materials to replace the conventional indium and platinum which have obvious disadvantages including high cost, complex fabrication, and chemical instability during the use. To this end, carbon nanotube (CNT)/polymer composite materials may represent one of the most promising candidates due to the combined advantages including high surface area, excellent electrical and electrocatalytic properties, and high stability from CNTs while good flexibility, abundant supply, and easy fabrication from polymers. In the current composite electrodes, however, CNTs are typically interconnected to form networks, and the generated charges have to hop through a lot of boundaries among CNTs. The resulting organic solar cells based on the CNT/polymer composite electrodes showed low efficiencies. Here we have developed a perpendicularly aligned and penetrated CNT/polymer composite film through a simple slicing technique. This novel composite film exhibits good transparency, high flexibility, excellent electrical conductivity, and remarkable electrocatalytic activity, and may be widely used for various electrode materials. As a demonstration, it was used as a counter electrode to fabricate dye-sensitized solar cells with high efficiency.