Hu Lin-Hua

Influence of Yb-Doped Nanoporous TiO2 Films on Photovoltaic Performance of Dye-Sensitized Solar Cells

Yb-doped TiO2 pastes with different Yb/TiO2 weight ratios are prepared in the sol-gel process to obtain dye-sensitized solar cells (DSCs). The nanocrystalline size of Yb-TiO2 becomes smaller and the lattice parameters change. Lattice distortion is observed and dark current is detected. It is found that a part of Yb existing as insulating oxide Yb2O3 state acts as barrier layers at the electrode–electrolyte interface to suppress charge recombination. A Yb-doped TiO2 electrode applied in DSCs leads to a higher open-circuit voltage and a higher fill factor. How the Yb-doped TiO2 films affect the photovoltaic response of DSCs is discussed.

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.

Metal chalcogenide complex-mediated fabrication of Cu2S film as counter electrode in quantum dot sensitized solar cells

Cu2S film onto FTO glass substrate was obtained to function as counter electrode for polysulfide redox reactions in CdS/CdSe co-sensitized solar cells by sintering after spraying a metal chalcogenide complex, N4H9Cu7S4 solution. Relative to Pt counter electrode, the Cu2S counter electrode provides greater electrocatalytic activity and lower charge transfer resistance. The prepared Cu2S counter electrode represented nanoflower-like porous film which was composed of Cu2S nanosheets on FTO and had a higher surface area and lower sheet resistance than that of sulfided brass Cu2S counter electrode. An energy conversion efficiency of 3.62% was achieved using the metal chalcogenide complex-mediated fabricated Cu2S counter electrode for CdS/CdSe co-sensitized solar cells under 1 sun, AM 1.5 illumination.

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.

Influence of Particle Coordination Number in Nanoporous TiO2 Films on the Performance of Dye-Sensitized Solar Cell Modules

The average particle coordination number, one of the characters concerning the pore size distribution in the films, was introduced in dye-sensitized solar cell (DSC) modules with the size of 15 cm × 20 cm and the active area of 187.2 cm2 to estimate the performance of a TiO2 nanoporous film, which is critical to the future DSC production. The current–voltage measurement of the DSC modules indicates that the average particle coordination number in the range of 4–5 typically appears in nanocrystalline TiO2 films used in the DSC modules and that the average coordination number could provide a very valuable way to evaluate the performance of nanoporous TiO2 films.

Influence of TiCl 4 nanoporous TiO 2 films on the performance of dye-sensitized solar cells

The mechanisms of electron transport and back-reaction in dye-sensitized solar cells (DSCSs) are investigated by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). The DSCSs with and without TiCl 4 -treated nanoporous TiO 2 films are measured by IMPS/IMVS. The results indicate that the electron lifetime ( τ n ), the diffusion coefficient ( D n ), the diffusion length ( L n ), the incident photon to current efficiency (IPCE) and the photoinduced charge ( Q oc ) increase markedly, while the dark current and the electron transit time ( τ d ) decreases for the TiCl 4 -treated nanoporous TiO 2 films. The influence of TiCl 4 -treatment of nanoporous TiO 2 film on the electron generation, the transport and the recombination processes is investigated at a microscopic level.