| Nowadays, mankind is faced with two big problems, environmental degradation and the energy crisis. Thus, green energy for the sustainable development has attracted the attention all over the world. The solar energy possesses the characteristics of widely distributed, environment friendly and inexhaustible, so it inevitably becomes an important part of energy used by man on earth. Solar cell is one of the most potential and development prospects in solar energy application. Among them, the quantum dot sensitized solar cell（QDSCs） is widely regarded as a kind of new type of solar cells with application potential. It has the advantages of simple technology, low cost and the high photoelectric conversion efficiency. However, compared with the traditional solar cells, the actual photoelectric conversion efficiency of QDSCs still needs further improve by seeking new materials and methods. QDSCs mainly consists of three parts: photo-anode, electrolyte and the electrode. The photo-anode absorbs photon to produce photon-generated carrier, and it is also in charge of transmission and collection of photo-generated electrons, so the photo-anode plays a vital role in photoelectric conversion efficiency.Titanium dioxide（Ti O2） as a perfect photo-anode material of solar cell, which possesses good chemical stability and proper conduction and valence band positions in aqueous solution. The size, morphology and crystal form of Ti O2 nano-semiconductor materials have close connection with their physical and chemical properties. Therefore, researchers prepare a variety of morphologies based on some aspect of outstanding performance of Ti O2 nanostructures. The advantage of one-dimensional nanostructure, such as nanotubes, nanorods, is that it provides direct electronic transmission channels to improve transmission speed of electron, and thus lower the recombination rate of photon-generated carrier. The advantages of two-dimensional and three-dimensional nanostructures, such as nano-sheets, nano-particles, are that the large specific surface area and strong surface activity can improve the adhesion of quantum dots. But Ti O2 is a kind of wide bandgap semiconductor material, which could only absorbs the ultraviolet area in total sun light. Researchers have tried many methods to broaden the photoresponse range of Ti O2 to visible area, which can be decided into two main categories. One way is doping non-metallic or metal atoms in Ti O2, introducing acceptor or donor level in the band gap of Ti O2 to expand the light absorption range, and thus it can trap photogenerated electrons more effectively and can reduce the recombination rate of electrons and holes; the other way is sensitizing Ti O2 with narrow-band-gap semiconductor material. Ti O2 and narrow-band-gap semiconductor quantum dot could form heterojunction, and the energy level shows ladder-like distribution. Then the photo-generated electrons could transfuse from conduction band position of quantum dots into the conduction band of Ti O2 effectively, promoting the rapid photo-generated electron pair separation.According to the viewpoints above, this study mainly consists of the following five aspects. Explore the impact of electrolyte concentration on the morphology and properties of Ti O2 nanotubes array film; How the Ti O2 nanotube-wires array film treated by alkali affects the morphology and performance; Investigate the influence of temperature on the morphology and properties of Ti O2 nanotubes array film treated hydrogen; Compare the properties of Bi2S3/Cd S quantum dot co-sensitized Ti O2 nanotube-wires array film treated by hydrogen or not; Build the structure of Bi2S3/Cd S/Ti O2 nanotube-wire-particles array film, and optimize its related properties. The research mainly include the following works:（1） By changing the concentration of fluoride ionin the electrolyte, we prepared three kinds of nanostructures through anodic oxidation method: nanotube-wire array film（TTW）, nanotube array film and nanotubes array film with porous film on the top. By comparison, TTW array possess the best photoelectronchemical performance, and the current density is 0.51 m A/cm2, photoconversion efficiency is 0.29. The nanotubes and nanowires are growth relationship, so the structure can keep the advantage of electron transfer between them, and can use the advantage of larger specific surface area of nanowires to contact with the electrolyte adequately as well and thus it promotes the separation of photoelectrons from vacancies effectively.（2） The prepared TTW array film was used to react with two kind alkaline reagents. We compared the influences to morphology and properties by reacting with Na OH solution and NH3·H2O solution in different time. When TTW array film reacts with Na OH for 10 min, the photoelectrochemical performance is the best, and the current density is 0.55 m A/cm2, photoconversion efficiency is 0.32; When it reacts with NH3·H2O solution for 20 min, we get the best current density of 0.95 m A/cm2, photoconversion efficiency is 0.64. Because the reaction speed between Ti O2 and NH3·H2O is slower than that of Na OH, and the reaction will not destroy the structure of TTW. The reaction makes the nanowires longer and the nanotube wall thinner, forming a hybrid construct of nanotubes array at the bottom and nanowires porou film at the top. The nanotubes and nanowires are still growth relationship. It has the following advantages:（a） The nanowires porou film at the top using the advantage of large specific surface to contact with the electrolyte adequately, and it can again utilize the reflected light by Ti base at the bottom to produce photo-generated electron pair as many as possible.（b） The nanotubes array have the advantage of less longitudinal interface to provide more direct electron transport channels to transmit the photo-generated carrier to the Ti substrate quickly, which effectively prolong the working life of electrons.（3） The prepared TTW array film was annealed in different temperatures in hydrogen atmosphere（H-TTW）. When the annealing temperature is 300 ℃, H-TTW has the best crystallinity, which possesses the strongest light absorption strength. The photoelectrochemical property is optimal with the current density of 1.02 m A/cm2,, photoconversion efficiency is 0.57. That is because the amounts of hydroxyl groups on the surface of TTW increase after dealing with the hydrogen, promoting the density of surface active center of TTW, thereby increasing the transfer rate from the hole on the surface of Ti O2 to electrolyte and, ultimately, improving the photoelectrochemical properties of H-TTW.（4） We adopted successive ionic layer adsorption and reaction（SILAR） method to sensitize TTW and H-TTW film by Cd S and Bi2S3 quantum dots, respectively. We discussed the influences of the cycles of quantum dot sensitization on photoelectron chemical performance. The TTW was first sensitized by Cd S quantum dots for 6 times, and then sensitized by Bi2S3 quantum dots for 3 times. The photoelectron chemical property is the best, and the current density is 3.75 m A/cm2, photoconversion efficiency is 2.9; The H-TTW was first sensitized by Cd S quantum dots sensitized for 4 times, and then sensitized by Bi2S3 quantum dots for 3 times. It possesses the maximum current density of 4.34 m A/cm2, photoconversion efficiency is 3.4. It can be devided into three major reasons:（a） Cd S and Bi2S3 are narrow band gap semiconductor materials. Using them as quantum dots sensitizer can extends the light absorption region to produce more photo-generated carrier.（b）The energy level of the heterojunction material of Bi2S3/Cd S/Ti O2 shows ladder-like distribution, so the photo-generated electrons on the conduction band of Bi2S3 can quickly transfer to Cd S, then to Ti O2, which can rapidly separate the electron-hole pairs.（c） The density of surface active center of H-TTW increases after hydrogen treatment, which speeds up the adsorption rate of Cd S quantum dots, resulting in that the Cd S quantum dots can reach peak form in a short time.（d） The higher density of Cd S quantum dots enlarge the area of Cd S/Ti O2 heterojunction significantly, which can improve the transfer rate of holes from Cd S quantum dots to electrolyte, ultimately increasing the current density correspondingly.（5） By using sol-gel method, we prepared Ti O2 nanoparticles film with different thickness on nanotube-wires array film（H-TTWP（e））. Then it was sensitized by Cd S and Bi2S3 quantum dot to build the composite film which are consisted of nanotubes-wire-particle, naming as Bi2S3（3）/Cd S（4）/H-TTWP（e）. When the number of dip-coating in Ti O2 sol is 6 times, Bi2S3（3）/Cd S（4）/H-TTWP（6） has the highest current density of 9.34 m A/cm2, photoconversion efficiency is 6.13. This is because Bi2S3（3）/Cd S（4）/H-TTWP（6） fully explore the advantages of nanotubes, nanowires and nanoparticles. Such as:（a） The nanoparticles film at the top can make full use of sunlight because of their large specific surface to absorb more quantun dots to improve the utilization of sunlight. Meanwhile, they also can again utilize the reflected light by Ti base at the bottom to produce photo-generated electron pair.（b） The nanotube array not only can produce photo-generated electron pair, but also can supply more direct electron transport channel for photo-generated electron produced by Bi2S3（3）/Cd S（4）/H-TTWP（6） by the advantange of samller interface to reduce the compound probability of electrons and holes.（c） The Ti O2 nanowires play an important role as a bridge, which can use their advantage of the large specific surface area to contact with nanoparticles film fully, making the nanoparticles film on top and the nanotube-wries array at bottom grow very well together to provide continuous transfer channels for electrons, and finally improving the photoelectrochemical performance. |
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