Junpeng Liu

Organic/inorganic hybrid solar cells with vertically oriented ZnO nanowires

Hybrid photovoltaic (PV) devices based on copper-phthalocyanine and fullerene combined with ZnO nanowire array as direct charge transport paths were fabricated. The optimized device with ZnO nanowire has a more than fourfold increase in PV performance than the device without nanowire. The former has an open circuit voltage of 0.46 V, a short circuit current of 3.86 mA/cm2, a fill factor of 0.30, and a power conversion efficiency of 0.53%. The hybrid device based on ZnO nanowires with improved PV performance suggests a way for fabrication of PV device with more exciton dissociation interface area and continuous carrier transport paths.

Charge transport in flexible solar cells based on conjugated polymer and ZnO nanoparticulate thin films

ZnO nanoparticulate thin films were fabricated on flexible indium tin oxide (ITO) covered polyethylene terephthalate (PET) substrates by spin coating technology and were used in flexible solar cells with a hybrid polymer, due to the benefit of low temperature processes. The flexible solar cells with a structure of PET/ITO/ZnO/regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/Ag have shown a photovoltaic performance with open circuit voltage of 0.56 V, short-circuit current density of 12.55 mA cm−2, fill factor of 0.36 and power conversion efficiency of 2.51%. The opposite J–V curves of the devices with ZnO and without ZnO were attributed to the opposite charge transport directions, which suggested the electron transport and hole blocking role of ZnO. The photoluminescence intensity of P3HT was totally quenched in the P3HT:PCBM thin film while there was no photoluminescence quench in the ZnO/P3HT double layer thin film, which clearly indicates that the exciton dissociation occurs at the interface between P3HT:PCBM instead of that between ZnO and P3HT. Therefore, it is reasonable to infer that the electrons transported to ZnO are from the lowest unoccupied molecular orbital (LUMO) of PCBM instead of the LUMO of P3HT according to the quenching experiment results combined with the J–V curve and energy level diagram. The identification of the charge transport directions and the exciton–dissociation interface will benefit the further improvement of photovoltaic performance by optimization of material selection, device design and process technology.

Highly Flexible and Sensitive Wearable E-Skin Based on Graphite Nanoplatelet and Polyurethane Nanocomposite Films in Mass Industry Production Available

Graphene and nanomaterials based flexible pressure sensors R&D activities are becoming hot topics due to the huge marketing demand on wearable devices and electronic skin (E-Skin) to monitor the human bodys actions for dedicated healthcare. Herein, we report a facile and efficient fabrication strategy to construct a new type of highly flexible and sensitive wearable E-Skin based on graphite nanoplates (GNP) and polyurethane (PU) nanocomposite films. The developed GNP/PU E-Skin sensors are highly flexible with good electrical conductivity due to their unique binary microstructures with synergistic interfacial characteristics, which are sensitive to both static and dynamic pressure variation, and can even accurately and quickly detect the pressure as low as 0.005 N/50 Pa and momentum as low as 1.9 mN·s with a gauge factor of 0.9 at the strain variation of up to 30%. Importantly, our GNP/PU E-Skin is also highly sensitive to finger bending and stretching with a linear correlation between the relative resistance change and the corresponding bending angles or elongation percentage. In addition, our E-Skin shows excellent sensitivity to voice vibration when exposed to a volunteers voice vibration testing. Notably, the entire E-Skin fabrication process is scalable, low cost, and industrially available. Our complementary experiments with comprehensive results demonstrate that the developed GNP/PU E-Skin is impressively promising for practical healthcare applications in wearable devices, and enables us to monitor the real-world force signals in real-time and in-situ mode from pressing, hitting, bending, stretching, and voice vibration.

Super-hydrophobic/icephobic coatings based on silica nanoparticles modified by self-assembled monolayers

A super-hydrophobic surface has been obtained from nanocomposite materials based on silica nanoparticles and self-assembled monolayers of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS) using spin coating and chemical vapor deposition methods. Scanning electron microscope images reveal the porous structure of the silica nanoparticles, which can trap small-scale air pockets. An average water contact angle of 163° and bouncing off of incoming water droplets suggest that a super-hydrophobic surface has been obtained based on the silica nanoparticles and POTS coating. The monitored water droplet icing test results show that icing is significantly delayed by silica-based nano-coatings compared with bare substrates and commercial icephobic products. Ice adhesion test results show that the ice adhesion strength is reduced remarkably by silica-based nano-coatings. The bouncing phenomenon of water droplets, the icing delay performance and the lower ice adhesion strength suggest that the super-hydrophobic coatings based on a combination of silica and POTS also show icephobicity. An erosion test rig based on pressurized pneumatic water impinging impact was used to evaluate the durability of the super-hydrophobic/icephobic coatings. The results show that durable coatings have been obtained, although improvement will be needed in future work aiming for applications in aerospace.

Solventless Synthesis of Bi2S3 Nanowires and their Application to Solar Cells

Orthorhombic Bi2S3 (bismuthinite) nanorods and nanowires were synthesized by the solventless thermolysis of bismuth alkylthiolate precursors. Reactions producing high aspect ratio nanowires were carried out in air at 225°C with the presence of a capping ligand species, octanoate. Nanorods with a lower aspect ratio were produced by the same approach with the addition of elemental sulfur at a lower temperature (~160°C). Current density –Voltage characterization of the devices under illumination with 500 W Xenon lamp showed the photovoltaic performance. Both the nanorods and the nanowires hybrid with the polymer show the improved photovoltaic performance than polymer only. As far as we know, we are the first to apply Bi2S3 nanorods and nanowires to solar cells with the structure of ITO/PEDOT:PSS/MDMO-PPV:Bi2S3/Al.

Robust Hydrophobic Surfaces from Suspension HVOF Thermal Sprayed Rare-Earth Oxide Ceramics Coatings

This study has presented an efficient coating method, namely suspension high velocity oxy-fuel (SHVOF) thermal spraying, to produce large super-hydrophobic ceramic surfaces with a unique micro- and nano-scale hierarchical structures to mimic natural super-hydrophobic surfaces. CeO2 was selected as coatings material, one of a group of rare-earth oxide (REO) ceramics that have recently been found to exhibit intrinsic hydrophobicity, even after exposure to high temperatures and abrasive wear. Robust hydrophobic REO ceramic surfaces were obtained from the deposition of thin CeO2 coatings (3–5 μm) using an aqueous suspension with a solid concentration of 30 wt.% sub-micron CeO2 particles (50–200 nm) on a selection of metallic substrates. It was found that the coatings’ hydrophobicity, microstructure, surface morphology, and deposition efficiency were all determined by the metallic substrates underneath. More importantly, it was demonstrated that the near super-hydrophobicity of SHVOF sprayed CeO2 coatings was achieved not only by the intrinsic hydrophobicity of REO but also their unique hierarchically structure. In addition, the coatings’ surface hydrophobicity was sensitive to the O/Ce ratio, which could explain the ‘delayed’ hydrophobicity of REO coatings.

Photoluminescence of Mn + doped GaAs

Photoluminescence is one of the most useful techniques to obtain information about optoelectronic properties and defect structures of materials. In this work, the room-temperature and low temperature photoluminescence of Mn-doped GaAs were investigated, respectively. Mn-doped GaAs structure materials were prepared by Mn+ ion implantation at room temperature into GaAs. The implanted samples were subsequently annealed at various temperatures under N2 atmosphere to recrystallize the samples and remove implant damage. A strong peak was found for the sample annealed at 950 °C for 5 s. Transitions near 0.989 eV (1254 nm), 1.155 eV (1074 nm) and 1.329 eV (933 nm) were identified and formation of these emissions was analyzed for all prepared samples. This structure material could have myriad applications, including information storage, magnet-optical properties and energy level engineering.