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One-dimensional single crystalline TiO2 nanotube arrays with different length are prepared, and transferred onto the FTO glass substrate with different concentration of Ti-precursor. The relationships between the concentration of Ti-precursor and the optical properties, as well as the photovoltaic performance of the as-prepared solar cells have been investigated. The optical absorption intensity is obviously enhanced and optical absorption edge is expanded to 800 nm for the CdSe/CdS/TiO2 NTs solar cells. In addition, 20 μm - CdSe/CdS/TiO2 NTs solar cells with 0.1 M Ti-precursor have the great photovoltaic conversion efficiency of 4.18%. The excellent photovoltaic performance is attributed to the suitable TiO2 connection layer from 0.1 M Ti-precursor and length of TiO2 NTs, which greatly enhances the electron-hole generation and charge transfer performance in the solar cells. Finally, the photovoltaic efficiency of the as-fabricated solar cells can be further enhanced to 4.51% through the ZnS passivation layer deposition.

Surface states are significant factor for the enhancement of electrochemical performance in CuInS 2 quantum dot sensitized photo-electrodes. DDT, OLA, MPA, and S 2− ligand capped CuInS 2 quantum dot sensitized photo-electrodes are prepared by thermolysis, solvethermal and ligand-exchange processes, respectively, and their optical properties and photoelectrochemical properties are investigated. The S 2− ligand enhances the UV–vis absorption and electron–hole separation property as well as the excellent charge transfer performance of the photo-electrodes, which is attributed to the fact that the atomic S 2− ligand for the interfacial region of quantum dots may improve the electron transfer rate. These S 2− -capped CuInS 2 quantum dot sensitized photo-electrodes exhibit the excellent photoelectrochemical efficiency and IPCE peak value, which is higher than that of the samples with DDT, OLA and MPA ligands.

TiO2 nanowire arrays are prepared on Ti wire by a hydrothermal process, which are co-sensitized with CuInS2/Mn-CdS quantum dots to fabricate the solar cells with Cu2S/brass as the counter electrode. The UV–Vis absorption spectra observe that the deposition of CuInS2/Mn-CdS quantum dots on the TiO2 photoanodes obviously improves its optical absorption properties. The influence of the length of TiO2 nanowire arrays is also investigated, which indicates that the solar cells with 20 μm TiO2 nanowire arrays in length have the best photovoltaic performance. The diameter of Cu2S/brass counter electrode has a significant influence on the illuminated area and electrocatalytic ability of the solar cells. For comparison, the fibrous CuInS2/Mn-CdS quantum dot co-sensitized solar cells using the Cu2S counter electrode of 100 μm in diameter exhibits a photovoltaic power conversion efficiency of 3.51 %.

Due to the one-dimensional single crystal array nanostructure and large surface area ratio, the TiO 2 nanowire arrays and Cu 2 S nanorod arrays are prepared to be used as the photoanodes and counter electrodes in the quantum dot sensitized solar cells. It is observed that the diameters of TiO 2 nanowire and Cu 2 S nanorod are 80 nm and 100-150 nm, respectively. The optical absorption of TiO 2 photoanodes are obviously enhanced after the quantum dots deposition. The incident photon to current conversion efficiency spectra and electrochemical impedance spectroscopy indicate high electron transfer rate of TiO 2 nanowire arrays and good electrocatalytic activity for polysulfide reduction and charge transfer of Cu 2 S nanorod arrays. Incorporating the TiO 2 nanowire arrays photoanode and Cu 2 S nanorod arrays counter electrode, the CuInS 2 /CdS quantum dot sensitized solar cell achieves a photovoltaic power conversion efficiency of 4.13% under one-sunlight illumination, which is higher than that of the device based on TiO 2 and Cu 2 S nanoparticle films (3.53%).

One-dimensional single crystalline TiO2 nanorod arrays with different lengths were prepared by controlling the hydrothermal cycles, which were successfully sensitized with CuInS2 quantum dots by assembly linking cycles, and their optical absorption properties and photoelectrochemical properties were investigated. 6 μm-TiO2 nanorod electrodes with the CuInS2 quantum dots sensitization of three linking cycles had the best photoelectrochemical properties and short-circuit current density, such as the short-circuit current density are 27.3 times higher than that of pure 6 μm-TiO2 nanorod electrodes. The reason may be attributed to the suitable internal surface area of TiO2 nanorod, with the increasing of the adsorption content of CuInS2 quantum dots to generate much more photo-induce electrons. Moreover, it will also enhance the interface connection between TiO2 nanorod and FTO conducting substrate, which favors to reduce the recombination of photo-induced electron–hole pairs.

The effect of ZnSe passivation layer is investigated in the CuInS2 quantum dot sensitized solar cells, which is used to improve the photovoltaic performance. The CuInS2 quantum dot sensitized TiO2 photo-anodes are prepared by assembly linking technique, and then deposited by the ZnSe passivation layer using the successive ionic layer absorption and reaction technique. The optical absorption edge and photoluminescence peak have slightly red-shifted after the passivation layer coating. Under solar light illumination, the ZnSe passivation layer based CuInS2 quantum dot sensitized solar cells have the higher photovoltaic efficiency of 0.95% and incident photon conversion efficiency response than that of pure CuInS2 based solar cells and ZnS passivation layer based solar cells, as the electron injection rate becomes faster after coating with ZnSe passivation layer.

Single crystal three-dimensional TiO2 nanodendrite arrays were prepared by a hydrothermal process, which were successfully sensitized with CuInS2 quantum dots as photo-anodes to fabricate the solar cells. The UV–vis absorption and photoluminescence spectra observe that the TiO2 nanodendrite based photo-anode structures are more efficient to improve the optical absorption properties and electron–hole separation. Electrochemical impedance spectra and photoluminescence decay analysis indicate that the TiO2 nanodendrite based solar cells structure have higher electron injection rate. Under full sunlight illumination, the CuInS2 quantum dot sensitized TiO2 nanodendrite arrays exhibit a photovoltaic power conversion efficiency of 1.26%, which has great improvement of JSC comparing with that of CuInS2 quantum dot sensitized with TiO2 nanoparticles and nanorods.

ZnSe passivation layer onto the CuInS2 quantum dots sensitized solar cells was introduced by the SILAR method. The photovoltaic performance was enhanced and the resistance was lower than without passivation layer or with ZnS layer.