Influence of interface modification on the performance of polymer/Bi2S3 nanorods bulk heterojunction solar cells

In this paper, bulk heterojunction photovoltaic devices based on the poly[2-methoxy-5-(3',7'-dimethyloctyloxy)- 1,4-phenylenevinylene] (MDMO-PPV):Bi2S3 nanorods hybrid material were present. To optimize the performance of the devices, the interface modification of the hybrid material that has a significant impact on the exciton dissociation efficiency was studied. An improvement in the device performance was achieved by modifying the Bi2S3 surface with a thin dye layer. Moreover, modifying the Bi2S3 surface with anthracene-9-carboxylic acid can enhance the performance further. Compared with the solar cells with Bi2S3 nanorods hybrid with the MDMO-PPV as the active layer, the anthracene-9carboxylic acid modified devices are better in performance, with the power conversion efficiency higher by about one order in magnitude.

Enhanced photocatalytic activity of TiO2 nano-structured thin film with a silver hierarchical configuration

TiO2 sol-gels with various Ag/TiO2 molar ratios from 0 to 0.9% were used to fabricate silver-modified nano-structured TiO2 thin films using a layer-by-layer dip-coating (LLDC) technique. This technique allows obtaining TiO2 nano-structured thin films with a silver hierarchical configuration. The coating of pure TiO2 sol-gel and Ag-modified sol-gel was marked as T and A, respectively. According to the coating order and the nature of the TiO2 sol-gel, four types of the TiO2 thin films were constructed, and marked as AT (bottom layer was Ag modified, surface layer was pure TiO,), TA (bottom layer was pure TiO,, surface layer was Ag modified), TT (pure TiO, thin film) and AA (TiO, thin film was uniformly Ag modified). These thin films were characterized by means of linear sweep voltammetry (LSV), X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy and transient photocurrent (I-ph). LSV confirmed the existence of Ago state in the TiO, thin film. SEM and XRD experiments indicated that the sizes of the TiO,, nanoparticles of the resulting films were in the order of TT > AT > TA > AA, suggesting the gradient Ag distribution in the films. The SEM and XRD results also confirmed that Ag had an inhibition effect on the size growth of anatase nanoparticles. Photocatalytic activities of the resulting thin films were also evaluated in the photocatalytic degradation process of methyl orange. The preliminary results demonstrated the sequence of the photocatalytic activity of the resulting films was AT > TA > AA > TT. This suggested that the silver hierarchical configuration can be used to improve the photocatalytic activity of TiO2 thin film.

CONTROLLED FORMATION AND CHARACTERISTICS OF INTERFACES IN GAAS/ALGAAS SINGLE QUANTUM-WELLS

The influence of heterostructure quality on transport and optical properties of GaAs/AlGaAs single quantum wells with different qualities was studied. In a conventional sample-A, the transport scattering time and the quantum scattering time are small and close to each other. The interface roughness scattering is a dominant scattering mechanism. From comparison between theory and experiment, interface roughness with fluctuation height 2.5 Angstrom and the lateral size of 50-70 Angstrom were estimated. For samples introducing superlattices instead of AlGaAs layers or by utilizing growth interruption, both the transport and PL measurements showed that interfaces were rather smooth in the samples. The two scattering times are much longer. The interface roughness scattering is relegated to an unimportant position. Results demonstrated that it is important to control the formation of heterostructures in order to improve the interface quality.

EFFECTS OF DEEP CENTERS AT PT SI INTERFACES AND HYDROGENATION

Electrical measurements were combined with surface techniques to study the Pt/Si interfaces at various silicide formation temperatures. Effects of deep centers on the Schottky barrier heights were studied. Hydrogen plasma treatment was used to passivate the impurity/defect centers at the interfaces, and the effects of hydrogenation on the Schottky barrier heights were also examined. Combining our previous study on the Pt/Si interfacial reaction, factors influencing the PtSi/Si Schottky barrier diode are discussed.

EXCIMER-LASER DOPING OF SPIN-ON DOPANT IN SILICON

Solid films containing phosphorus impurities were formed on p-type silicon wafer surface by traditional spin-on of commercially available dopants. The doping process is accomplished by irradiating the sample with a 308 nm XeCl pulsed excimer laser. Shallow junctions with a high concentration of doped impurities were obtained. The measured impurity profile was ''box-like'', and is very suitable for use in VLSI devices. The characteristics of the doping profile against laser fluence (energy density) and number of laser pulses were studied. From these results, it is found that the sheet resistance decreases with the laser fluence above a certain threshold, but it saturates as the energy density is further increased. The junction depth increases with the number of pulses and the laser energy density. The results suggest that this simple spin-on dopant pre-deposition technique can be used to obtain a well controlled doping profile similar to the technique using chemical vapor in pulsed laser doping process.

THE ADSORPTION OF O2 ON FESI SURFACES

The initial adsorption stages and the interaction of oxygen on FeSi surfaces have been studied as a function of exposure and annealing temperature using a variety of techniques including HREELS, AES, LEED, XPS and UPS. O2 was found to adsorb dissociatively on the FeSi surfaces at room temperature. The whole adsorption process can be divided into four stages. Heating promotes the oxidation of Si, and a thin SiO2 overlayer is formed on the surface when annealed at 450-degrees-C, while all FeOx species are reduced. Models for adsorbed atomic O on the FeSi(100) surface exposed to different oxygen exposures have been put forward to account for the observed experimental results.

A NEW METHOD FOR MEASURING THE EFFECTIVE DIFFUSION CONSTANT OF 2-DIMENSIONAL ELECTRONS IN THE PRESENCE OF MAGNETIC-FIELDS

The transient charge response Q(t) of a two-dimensional electron gas (2DEG) in GaAs/AlxGa1-xAs heterostructures to a small pulse of the gate voltage, applied between the top gate and source electrodes in a Corbino structure, was employed to directly measure the effective diffusion constant of a 2DEG in the quantum Hall regime. The measured diffusion constant D showed a drastic change as the magnetic field was swept through the integer fillings of the Landau levels.

PHOTOEMISSION-STUDY OF THE INTERFACIAL FORMATION PROCESS AND REACTIONS BETWEEN AL AND HYDROGENATED AMORPHOUS SI

Using photoemission spectroscopy and Auger electron spectroscopy, the interfacial formation process and the reactions between Al and hydrogenated amorphous Si are probed, and annealing behaviors of the Al/a-Si:H system are investigated as well. It is found that a three-dimensional growth of Al metal clusters which includes reacted Al and non-reacted metal Al occurs at the initial Al deposition time, reacted Al and Si alloyed layers exist in the Al/a-Si:H interface, and non-reacted Al makes layer-by-layer growth forming a metal Al layer on the sample surface. The interfacial reactions and element interdiffusion of Al/a-Si:H are promoted under the vacuum annealing.