Preparation Of Well Distributed And Core Double Shell Structured Quantum Dots In Water And Their Film Deposition With Graphene

Quantum dots (QDs) is a type of colloid semiconductor nanocrystal. Once it is excited, its electrons at conduction band (CB), holes at valence band and excitons are restricted in three dimension directions. There are wide developed foregrounds for QDs in solar cells, light-emitting dipoles and biomedicine areas. Synthesis of high quality QDs is a very hot research topic because the property of QDs, such as fluorescence efficiency, spectrum response range and aqueous solubility restricts the research of applications and results. The research aims to synthesize QDs with narrow size distribution and wide spectrum response range and deposit thin film with QDs and graphene in turn in order to get full use of solar energy.Synthesis of QDs in water takes many advantages, but the fluorescence efficiency is comparatively low due to wide particle size distribution. Aqueous route for QDs synthesis is optimized in order to get QDs with narrow size distribution. The block copolymer P123 is used as template according to lyotropic liquid crystal principle. Inerratic pore by micelle can be formed when the concentration is higher than CMC. Cd precursor and NaHTe (NaHSe) or S precursor is added into the well-prepared template solution respectively. QDs with narrow size distribution can be obtained because nucleation and growth of QDs take place inside of the inerratic pore. The precursor molar ratio, origin pH value of solution and three different templates are discussed and characterized by spectrum methods. QD of CdTe, particle size ranging from 2.5 to 3 nm, is synthesized under the molar ratio of 1:2.4:0.25(Cd2+: thioglycollic acid:Te) in the solution which pH value is 9. It can be turned out that narrow size distribution QDs can be synthesized with templates.One of the issues that leads to low utilization efficiency of solar energy, particularly to the long wave and infrared region energy is narrow spectrum response range. Although absorption and emission of QDs can red shift with the growth of particle size, QDs with large diameter become unstable in water. The larger particles become, the sooner QDs get precipitated in water. Absorption and emission wave length of core-shell-shell structured QDs can be tuned significantly by the difference of electrons band edge and thickness of outmost shell. Two different core-shell-shell structured QDs are designed and synthesized by the method of Successive Ionic Layer Adsorption and Reaction coupling Thermal Cycling (SILAR-TC). Absorption and emission of the former one get red shift (almost 100nm at most), and those of the latter one get blue shift with thickness increase of outmost shell. QDs with less than ten monolayers of outmost shell are very stable in water, which can be maintained under normal conditions for one than one year.Electrons are transported with very high speed by grapheme which distinguishes itself by single slide structure. Graphene can be easily assembled and fabricated with other material because there are active groups one both side of one slide. Thin film of graphene is deposited onto ITO glass by Electrophoretic Deposition (ED) technique and Layer-by-layer (LBL) technique. QDs with different fluorescence property and graphene are deposited onto ITO glass in turn by LBL method. The hybridized thin film can display higher solar energy conversion efficiency because electron-hole pair can be further separated due to high speed transportation of electrons by graphene. UV-VIS and SEM indicate that graphene can be reduced from oxidized graphene by hydrazine hydrate and Vitamin C. SEM photos demonstrate that graphene is deposited with good uniformity, and QDs are fabricated with graphene forming homogeneous thin film.QDs of CdTe,CdSe and CdS with narrow size distribution confined by template of three block copolymer P123 are synthesized under optimized precursor molar ratio and origin pH value. CdSe-CdTe-ZnSe and CdTe-CdSe-ZnSe, which are two type of core-shell-shell structured QDs are designed and synthesized by SILAR-TC method. One of the distinguished properties of them is that absorption and emission wavelength can be tuned by changing the thickness of outmost shell. The obtained QDs and graphene are deposited onto ITO glass forming homogeneous thin film. The hybridized film provides a good method for making QDs intermingled solar cells.