Cadmium sulfide (CdS) and cadmium selenide (CdSe) quantum dots (QDs) are sequentially assembled onto a nanocrystalline TiO2 film to prepare a CdS/CdSe co‐sensitized photoelectrode for QD‐sensitized solar cell application. The results show that CdS and CdSe QDs have a complementary effect in the light harvest and the performance of a QDs co‐sensitized solar cell is strongly dependent on the order of CdS and CdSe respected to the TiO2. In the cascade structure of TiO2/CdS/CdSe electrode, the re‐organization of energy levels between CdS and CdSe forms a stepwise structure of band‐edge levels which is advantageous to the electron injection and hole‐recovery of CdS and CdSe QDs. An energy conversion efficiency of 4.22% is achieved using a TiO2/CdS/CdSe/ZnS electrode, under the illumination of one sun (AM1.5,100 mW cm−2). This efficiency is relatively higher than other QD‐sensitized solar cells previously reported in the literature.

An efficient photoelectrode is prepared by sequentially assembled CdS and CdSe quantum dots (QDs) onto a nanocrystalline TiO 2 film. The CdS/CdSe co-sensitized photoelectrode was found to have a complementary effect in the light absorption. Furthermore, the cascade structure, TiO 2 /CdS/CdSe, exhibits a significant enhancement in the current-voltage response, both in dark conditions and under light illumination. On the contrary, the performance of the reverse structure, TiO 2 /CdSe/CdS, is much less than the electrode using a single sensitizer. The open circuit potentials measured in the dark for these electrodes indicates that a Fermi level alignment occurs between CdS and CdSe after their contact, causing downward and upward shifts of the band edges, respectively, for CdS and CdSe. A stepwise band edge structure is, therefore, constructed in the TiO 2 /CdS/CdSe electrode, which is responsible for the performance enhancement of this photoelectrode. The saturated photocurrent achieved by the TiO 2 /CdS/CdSe electrode under the illumination of UV cutoff AM1.5 (100 mW/cm 2 ) is 14.9 mA/cm 2 , which is three times the value obtained by the TiO 2 /CdS and TiO 2 /CdSe electrode. When a ZnS layer is further deposited for passivating the QDs, the corresponding hydrogen evolution rate measured for the TiO 2 /CdS/CdSe/ZnS electrode is 220 μmol/(cm 2 h) (5.4 mL/(cm 2 h)). This performance is presently the highest reported for the QD-sensitized photoelectrochemical cells.

Alcohol, instead of water, was used as a solvent in a chemical bath deposition process for the in situ synthesis of CdS quantum dots onto mesoporous TiO 2 films. Due to low surface tension, the alcohol solutions have high wettability and superior penetration ability on the mesoscopic TiO 2 film, leading to a well-covered CdS on the surface of mesopores. The CdS-sensitized TiO 2 electrode prepared using the alcohol system not only has a higher incorporated amount of CdS but also greatly inhibits the recombination of injected electrons. The efficiency of a CdS quantum-dots-sensitized solar cell prepared using the present method is as high as 1.84% under the illumination of one sun ͑AM1.5, 100 mW/ cm 2 ͒.

No abstract

A facile method using layer-by-layer assembly of silica particles is proposed to prepare raspberry-like particulate films for the fabrication of superhydrophobic surfaces. Silica particles 0.5 microm in diameter were used to prepare a surface with a microscale roughness. Nanosized silica particles were then assembled on the particulate film to construct a finer structure on top of the coarse one. After surface modification with dodecyltrichlorosilane, the advancing and receding contact angles of water on the dual-sized structured surface were 169 and 165 degrees , respectively. The scale ratio of the micro/nano surface structure and the regularity of the particulate films on the superhydrophobic surface performance are discussed.