Luo Xiang-Dong

Influence of Different Surface Modifications on the Photovoltaic Performance and Dark Current of Dye-Sensitized Solar Cells

The TiO2 nanoporous film photoelectrode, as a crucial component of dye-sensitized solar cells, has been investigated. The photovoltaic properties and the dark current were studied by two surface modification methods. One was to apply a compact layer between the conductive glass substrate and nanoporous TiO2 film. Another was to produce TiO2 nanoparticles among the microstructure by TiCl4 treatment. A suitable concentration and number of times for TiCl4 treatment were found in our experiment. The dark current is suppressed by surface modifications, leading to a significant improvement in the solar cells performance. An excessive concentration of TiCl4 will produce more surface states and introduce a larger dark current reversely. The dye is also regarded as a source of charge recombination in dark to some extent, due to an amount of surface protonations introduced by the interfacial link in the conductive glass substrate/dye interface and dye/TiO2 interface.

The Electric Mechanism of Surface Pretreatments for Dye-Sensitized Solar Cells Based on Internal Equivalent Resistance Analysis

Based on the optimization of dye-sensitized solar cell (DSC) photoelectrodes pretreated with different methods such as electrodeposition, spin-coating and TiCl4 pretreatment, theoretical calculations are carried out to interpret the internal electric mechanism. The numerical values, including the series resistance Rs and the shunt resistance Rsh corresponding to the equivalent circuit model, are well evaluated and confirm that the DSC has good performance with a high Rsh and a low Rs due to good electrical contact and a low charge recombination after the different modifications. The I-V curves are fitted in the case without series resistance, and account for the role of Rs in the output characteristics. It is found that when Rs tends to the infinitesimal, the short-circuit current Isc, the open-circuit voltage Voc and the fill factor can be improved by almost 0.8–1.4, 2.9 and 2.1–6.8%, respectively.

A Study on Porosity Distribution in Nanoporous TiO2 Photoelectrodes for Output Performance of Dye-Sensitized Solar Cells

Porosity as one of the crucial factors to film morphology affects the overall electrical current-voltage characteristics of dye-sensitized solar cell (DSC). We search for the short-circuit current density, the open-circuit voltage and the maximum power output as the main functional parameters of DSC closely related to porosity under different film thickness. The theoretical analyses show some exciting results. As porosity changes from 0.41 to 0.75, the short-circuit current density shows the optimal value when the film thickness is 8–10 μm. The open-circuit voltage presents different variation tendencies for the film thicknesses within 1–8 μm and within 10–30 μm. The porosity is near 0.41 and the film thickness is about 10 μm, DSC will have the maximum power output. The theoretical studies also illustrate that given a good porosity distribution, DSC can obtain an excellent short-circuit current characteristic, which agrees well with the experimental results reported in previous literature.

Effect of Reactor Pressure on Qualities of GaN Layers Grown by Hydride Vapour Phase Epitaxy

The influence of reactor pressure on GaN layers grown by hydride vapour phase epitaxy (HVPE) is investigated. By decreasing the reactor pressure from 0.7 to 0.5 atm, the GaN layer growth mode changes from the island-like one to the step flow. The improvements in structural and optical properties and surface morphology of GaN layers are observed in the step flow growth mode. The results clearly indicate that the reactor pressure, similarly to the growth temperature, is one of the important parameters to influence the qualities of GaN epilayers grown by HVPE, due to the change of growth mode.