Chan Luo

High-performance polymer heterojunction solar cells of a polysilafluorene derivative

High-performance polymer heterojunction solar cells fabricated from an alternating copolymer of 2,7-silafluorene (SiF) and 4,7-di(2′-thienyl)-2,1,3-benzothiadiazole (DBT) (PSiF-DBT) as the electron donor blended with [6,6]-phenyl-C61-butyric acid methyl ester as the electron acceptor were investigated. A power-conversion efficiency up to 5.4% with an open-circuit voltage of 0.90V, a short-circuit current of 9.5mAcm−2, and a fill factor of 50.7% was achieved under the illumination of AM 1.5G from a calibrated solar simulator (800Wm−2). The field-effect transistors fabricated from PSiF-DBT showed a high hole mobility of ∼1×10−3cm2V−1s−1.

Flexible Carbon Nanotube-Polymer Composite Films with High Conductivity and Superhydrophobicity Made by Solution Process

CNT/Nafion nanocomposite film made by solution process exhibits high conductivity and superhydrophobicity. The highest water contact angle reaches 165.3 +/- 1.9 degrees. The wettability of the film can be controlled by simply varying the filtering rate and the content ratio of Nafion to CNT. We also develop a novel optical method to directly observe the air-solid-liquid interface for the first time. The extraordinary mechanical strength provided by the polymer helps the film retain its conductivity and superhydrobicity after 1000 bending cycles.

All-solution processed polymer light-emitting diode displays.

Adopting the emerging technology of printed electronics in manufacturing novel ultrathin flat panel displays attracts both academic and industrial interests because of the challenge in the device physics and the potential of reducing production costs. Here we produce all-solution processed polymer light-emitting diode displays by solution-depositing the cathode and utilizing a multifunctional buffer layer between the cathode and the organic layers. The use of ink-jetted conducting nanoparticles as the cathode yields high-resolution cathode patterns without any mechanical stress on the organic layers. The buffer layer, which offers the functions of solvent-proof electron injection and proper affinity, is fabricated by mixing the water/alcohol-soluble polymer and a curable epoxy adhesive. Our 1.5-inch polymer light-emitting diode displays are fabricated without any dead pixels or dead lines. The all-solution process eliminates the need for high vacuum for thermal evaporation of the cathode, which paves the way to industrial roll-to-roll manufacturing of flat panel displays.

High-efficiency polymer photovoltaic devices from regioregular-poly(3-hexylthiophene-2,5-diyl) and [6,6]-phenyl-C61-butyric acid methyl ester processed with oleic acid surfactant

Bulk heterojunction photovoltaic cells, comprised of regioregular-poly(3-hexylthiophene-2,5-diyl) (P3HT) and[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in the presence of the surfactant, oleic acid (OA), have been studied. The device with OA after thermal annealing has a power conversion efficiency (ηe) of 4.3%, while the devices without OA after thermal annealing have ηe=3.1%. Based on atomic force microscopy, x-ray diffraction investigation found that with OA, the P3HT-PCBM films have better molecular local ordering after thermal annealing resulting in larger donor and acceptor interfaces and higher mobility, thereby higher performance of the photovoltaic cell.

Direct Three‐Dimensional Imaging of the Buried Interfaces between Water and Superhydrophobic Surfaces

The investigation of how water interacts with hydrophobic solids is crucial for understanding many natural and technological phenomena, such as hydrophobic collapse in protein folding, the formation of hydrophobic clays, and superhydrophobicity. While it is generally believed that air is trapped at the interfaces between water and superhydrophobic (SH) surfaces, direct experimental evidence for the presence of air at the microscopic level is rare. Herein we present an in situ, nondestructive approach to the direct 3D imaging of the buried interfaces between water droplets and superhydrophobic surfaces by confocal laser scanning microscopy (CLSM). A 10 mm thick air cushion trapped at the interface is quantitatively visualized and shown to be responsible for the ultralow-resistance fluid flow. The two intangible hydrophobic states, that is, Wenzel and Cassie states, can be distinctly identified by this advanced technique. Our new approach also opens a pathway to explore complex phenomena and regulate subtle processes that occur at the liquid–vapor–solid interface for various basic research and industrial applications. Inspired by natural examples (e.g., lotus leaves and water strider legs), the design of artificial SH surfaces by fabricating rough surface microstructures and decorating the microstructured surface with chemicals of low surface free energy has become a popular research focus, since SH surfaces have found important applications in fields from aquatic devices, microfluidic transport, and protective coatings, to proteins and DNA analysis. The superhydrophobicity of the surfaces has been explained by two major mechanisms, assuming that water exists in either Wenzel or Cassie states on hydrophobic surfaces. In the Wenzel state, water is in intimate contact with the rough surface; the contact area is dominated by the liquid–solid interface, and water droplets adhere to the solid with both large contact angles (CAs) and rolling angles (RAs). In the Cassie state, the existence of the additional liquid–vapor interface means that water is partial contact with the solid, so that droplets have large CAs but small RAs. Although the two mechanisms have long been proposed for the analysis of SH surfaces, it is still a matter of debate as to which state dominates in different circumstances, owing to the lack of a direct, quantitative observation method and in-depth insights into the buried interface. The interface below the liquid cannot be imaged by using techniques such as SEM, TEM, and AFM, while conventional 2D optical observation provides only limited and nonquantitative information that is insufficient for constructing the whole picture of the topologically complex buried interface.

High-performance, all-solution-processed organic nanowire transistor arrays with inkjet-printing patterned electrodes.

Organic nanowire (NW) transistor arrays with a mobility of as high as 1.26 cm(2)·V(-1)·S(-1) are fabricated by combining the dip-coating process to align the NW into arrays with the inkjet printing process to pattern the source/drain electrodes. A narrow gap of ~20 μm has been obtained by modifying the inkjet process. The all-solution process is proven to be a low-cost, high-yield, simple approach to fabricating high-performance organic NW transistor arrays over a large area.

A solution process for size-controlled growth and transfer of organic nanostructures with manufacture scalability.

A simple and robust process has been developed to control the growth of the organic nanowires in situ self-assembled in a polymer matrix, lift off the nanostructure/polymer composite film from the mother substrate for storage and transfer, and remove the polymer host prior to usage. Every step was completed through a solution process, which ensured the processs simplicity and low cost. The realization of large-sized nanowire/polymer composite film demonstrated the necessary process scalability required by the industrial roll-to-roll manufacturing.

Photovoltaic effect and its polarity in Si doping superlattices

We have studied the photovoltaic effects in Si doping superlattices (nipi) under different excitation conditions with and without additional cw optical biasing using a He-Ne laser. On the basis of the photovoltaic theory of carrier spatial separation in superlattices, we propose the concept of spatial fixity of the photovoltage polarity in type-II superlattices and examine the experimental results. The photovoltaic effect in Si nipi is found mainly from the direct transitions related with shallow impurities in real space, not the electron-hole band-to-band process as in GaAs nipi.