•Large enhancement of the cell efficiency of CdSe sensitized ZnO QDSSC is achieved by introducing ZnSe overcoating layer.•The thickness of ZnSe was found to be crucial.•The enhancement effect of ZnSe overcoating is superior to ZnS overcoating.•The role of ZnSe overcoating is ascribed to the suppression of surface/interface defects in photoanode.Charge recombination is an important factor that limits the cell efficiency of quantum dot sensitized solar cells (QDSSCs). Herein, we report a facile way to improve the cell performance of CdSe sensitized ZnO QDSSC by overcoating a thin layer of ZnSe on CdSe/ZnO film through a successive ionic layer adsorption and reaction (SILAR) procedure. Photovoltaic investigations indicate that ZnSe overcoating can increase photocurrent and photovoltage of the cell, resulting in significant enhancement of the cell efficiency, which is much better than the widely used traditional ZnS material. The superior role of ZnSe overcoating is ascribed to its large inhibition of charge recombination loss owing to its suitable band structure, efficient passivation of ZnO and CdSe QDs as well as its small lattice mismatch with CdSe that leads to the large decrease of surface/interface defects in CdSe/ZnO photoanode. This finding provides an alternative efficient way to enhance the cell performance of ZnO based QDSSC by suppressing the charge recombination.

We report a study on anion exchange reaction of CdTe nanocrystals with S2− in aqueous solution under ambient condition. We found that the optical properties of CdTe nanocrystals can be well tuned by controlling the reaction conditions, in which the reaction temperature is crucially important. At low reaction temperature, the product nanocrystals showed blue-shifts in both absorption and PL spectra, while the photoluminescence quantum yield (PLQY) was significantly enhanced. When anion exchanges were carried out at higher reaction temperature, on the other hand, obvious red shifts in absorption and PL spectra accompanied by a fast increase followed by gradual decrease in PLQY were observed. On variation of S2− concentration, it was found that the overall kinetics of Te2− for S2− exchanges depends also on [S2−] when anion exchanges were performed at higher temperature. A possible mechanism for anion exchanges in CdTe NCs was proposed.

•Photoluminescence (PL) enhancement was observed by irradiating CdTe nanocrystals.•Light intensity and pyridine was found to be crucial.•Further improving of the PL was achieved when keeping the illuminated CdTe in dark.•A competition mechanism was suggested.We report an efficient way to improve the photoluminescence (PL) of water-soluble CdTe nanocrystals (NCs) by irradiating the NCs in the presence of pyridine. Under illumination, continuous increases in PL of CdTe NCs were observed. The maximum quantum yield reached up to 41% was obtained, showing five times higher than that of the as prepared parent CdTe NCs. While keeping the illuminated CdTe NCs in dark, further increase in PL quantum yield to over 60% was observed. PL decay measurements revealed that the PL enhancement is associated with the increase of the average lifetime of CdTe NCs. The effects of light wavelength and intensity, pyridine derivatives as well as oxygen on the PL of CdTe NCs were investigated, and a competition mechanism between photodegradation and surface passivation of CdTe NCs induced by illumination and pyridine was suggested.

TiO2 sub-micrometer spheres and size-tunable TiO2 rods with pure anatase phases have been prepared through a combined hydrolysis and hydrothermal process by simply controlling the reaction composition. The TiO2 spheres are highly porous structures possessing a large surface area, whereas TiO2 rods are single crystalline demonstrating excellent electron transfer and light scattering abilities. The product materials were utilized to form a bilayer structured photoanode incorporated in a dye-sensitized solar cell (DSSC). Under global AM 1.5 solar irradiation, a high overall solar energy conversion efficiency of 9.23% was achieved for the resultant DSSC, significantly higher than those cells derived from both TiO2 spheres (7.29%) and P25 particles (6.52%). The large improvement in cell performance is ascribed to the enhanced light harvesting and charge collecting capability along with the lowered charge recombination, resulting from the synergetic effect of TiO2 rods and spheres.

A dual post-treatment was carried out by introducing CdS sandwiched between quantum dots (QDs) and ZnS, which leads to a large increase in photocurrent for CdS/CdSe sensitized solar cells, resulting from the improved electron injection from QDs to TiO2. As a result, a high solar-to-energy conversion efficiency of 5.47% was achieved.

A new method for preparing platinum-modified electrodes by attracting nanometer-sized platinum particles from hydrosol to –SH coated surface of conductive glass obtained through Langmuir technique has been proposed. The electrode possessed a surface modified with homogeneously distributed platinum nanoclusters and a low platinum loading. The catalytic activity of thus fabricated electrode for the triiodide reduction was investigated by electrochemical impedance measurements. The charge-transfer resistance at the interface of electrolyte/electrode was much lower and the corresponding exchange current density was several hundreds micro ampere per centimeter square larger than conventional thermal decomposed Pt-modified electrode and Pt foil electrode.

TiO2 sub-micrometer spheres and size-tunable TiO2 rods with pure anatase phases have been prepared through a combined hydrolysis and hydrothermal process by simply controlling the reaction composition. The TiO2 spheres are highly porous structures possessing a large surface area, whereas TiO2 rods are single crystalline demonstrating excellent electron transfer and light scattering abilities. The product materials were utilized to form a bilayer structured photoanode incorporated in a dye-sensitized solar cell (DSSC). Under global AM 1.5 solar irradiation, a high overall solar energy conversion efficiency of 9.23% was achieved for the resultant DSSC, significantly higher than those cells derived from both TiO2 spheres (7.29%) and P25 particles (6.52%). The large improvement in cell performance is ascribed to the enhanced light harvesting and charge collecting capability along with the lowered charge recombination, resulting from the synergetic effect of TiO2 rods and spheres.

A dual post-treatment was carried out by introducing CdS sandwiched between quantum dots (QDs) and ZnS, which leads to a large increase in photocurrent for CdS/CdSe sensitized solar cells, resulting from the improved electron injection from QDs to TiO2. As a result, a high solar-to-energy conversion efficiency of 5.47% was achieved.