•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.

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.

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.

ZnO crystals were grown through a solution-based chemical route at ambient pressure and low temperature. It was found that the solution pH is a dominative factor in determining the morphology of crystals: Rod-like ZnO crystals are apt to be formed at near neutral condition, whereas flower-like structured ZnO crystals are preferred to be formed at higher solution pH. By monitoring the reaction intermediates during the ZnO growth process, it was realized that the crucial role of solution pH in determining the morphology of ZnO crystals is to control the structure of the primary reaction intermediates at the early stage of ZnO growth. Moreover, by appreciate controlling the solution pH together with Zn2+ concentration, various ZnO crystals of rod-like, dumbbell-like and even more complex flower-like structures were obtained without any template, and a pH-dependent morphology controllable growth mechanism is suggested.

The complete reversible phase transfer of TGA-capped CdTe NCs between aqueous and chloroform in the presence of 1-hexadecylamine (HDA) is demonstrated. It was found that the primary amine HDA is crucial in initiating the reversible phase transfer. FTIR measurements suggest that the phase transfer reversibility results from the reversible modification of CdTe NCs through the formation of surface –COONH3– complexes. UV-Vis investigations indicate that the transfer efficiency of CdTe NCs from aqueous to chloroform is dependent on the HDA concentration and the diameter of CdTe NCs. XRD and PL studies show that the particle size and distribution of CdTe NCs are retained, while the PL intensity of CdTe NCs is enhanced after the reversible phase transfer.

The complete reversible phase transfer of TGA-capped CdTe NCs between aqueous and chloroform in the presence of 1-hexadecylamine (HDA) is demonstrated. It was found that the primary amine HDA is crucial in initiating the reversible phase transfer. FTIR measurements suggest that the phase transfer reversibility results from the reversible modification of CdTe NCs through the formation of surface –COONH3– complexes. UV-Vis investigations indicate that the transfer efficiency of CdTe NCs from aqueous to chloroform is dependent on the HDA concentration and the diameter of CdTe NCs. XRD and PL studies show that the particle size and distribution of CdTe NCs are retained, while the PL intensity of CdTe NCs is enhanced after the reversible phase transfer.

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.

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.