Papers by Keyword: CdSe

Abstract: In this research, Zn_1-xCd_xSe alloys (x from 0 to 1) were synthesized by solid-state microwave (SSM) method of producing thermally evaporated thin films. The cubic structure and the elemental ratios of the films were studied using X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The optical characterizations of the as-deposited film in terms of the energy band gap (Eg), photoluminescence (PL), and Raman shift spectra were conducted at the room temperature. The Eg values for the thin films from ZnSe to CdSe were 3.4 to 1.7 eV, respectively. The PL orange emission for ZnSe thin film at 565 nm, whereas 590 nm in the yellow region for CdSe thin film. From Raman shift spectra, the two longitudinal-optical phonon modes (1LO and 2LO) at 240, and 490 cm^-1 are assigned for the ZnSe and CdSe thin films.

Abstract: Colloidal CdSe Nanocrystals (NCs) or quantum dots (QDs) have been developed using a yielding solution technique utilizing chemical reactions in chloroform and oleic acid in different organic solvents. This assembly is an improvement of the systematic thermal decomposition of high temperature organic solvent compounds. CdSe NCs of specific sizes can be produced easily by adjusting the solvent. This technique is reproducible and clear, so industrial development can be easily scaled up. Characterization at room temperature of the UV-Vis absorption and Photoluminescence (PL) spectra. Results reveal that the CdSe prepared with the creation of defects was nanocrystalline. The energy difference (Eg) measured in PL was 2.3 and 2.69 eV respectively for CdSe NCs in chloroform and oleic acid. The structures of the CdSe quantum dots were determined by scanning electron microscopy (SEM). The phase-transfer of chloroform and oleic acid stabilized CdSe nanocrystals solutions was studied for their potentials in white light generation applications.

Abstract: New nanocrystals (NCs) were engineered with a core/shell/shell system consisting of CdSe core/ CdTe shell/ CdS shell. The white light generation mechanism was described depending on mixing colors from the illuminated CdSe/CdTe/CdS core/shell/shell nanocrystals. The color mixed in CdSe/CdTe/CdS core/shell/shell NCs system were used to generate extreme white light when illuminated by InGaN/GaN UV LED (λ=360 nm) the core/shell/shell NCs system tuned the chromaticity coordinates to (0.332, 0.340) and increased the intensity of the emitted white light. The synthesis of the CdSe/CdTe/CdS core/shell/shell NCs were confirmed by SEM, AFM, XRD and photoluminescence (PL) experiments due to create of surface states defects information. This enhancement was recognized to the overlap of emission with the photoluminescence (PL) spectrum of CdSe/CdTe/CdS core/shell/shell NCs which indications to a cold white light generation. Current-voltage (I–V) characteristics indicate that the output current is good compared to the few voltages (6 V) used which give acceptable results to get a generation of white light.

Abstract: In the present study, we have computed the electronic band structure and electronic charge density of the alloy (Be, Cd)Se in the zinc-blende structure; using the local Empirical Pseudopotential Method (EPM), which takes into account the disorder effect into the Virtual Crystal Approximation (VCA) by introducing an effective potential disorder. The obtained results show a reasonable agreement with the available experimental data. Detailed plots of the valence charge distribution along the [111] direction and in the (110) plane are also presented and discussed.

Abstract: In this work, the development of solution-processed bulk heterojunction hybrid solar cells based on CdSe quantum dot (QD) and conjugated polymer poly [2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b] dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], PCPDTBT was performed. The photoactive layer was formed by integrating CdSe QDs onto multiwalled carbon nanotubes (CNTs). A simple method of thiol functionalization in the interface CNTs and CdSe QDs has been investigated. Integration of CNTs enhances long-term performance of solar cells devices. Initial PCE values of about 1.9 % under AM1.5G illumination have been achieved for this hybrid CNT-CdSe photovoltaic device. In addition, the long-term stability of the photovoltaic performance of the devices was investigated and found superior to CdSe QD only based devices. About 84 % of the initial PCE remained after storage in a glove box for one year without any further encapsulation. It is concluded that the improvement is mainly due to a strong binding between thiol functionalized CNTs and CdSe QDs, resulting preservation of the nanomorphology of the hybrid film over time.

Abstract: The morphological and structural transitions in CdSe hollow nanoparticles (hNPs) with zinc blende structure have studied by molecular dynamics (MD) simulation method under heating. The seven samples of CdSe-hNPs are constructed with different thicknesses from the solid NPs at 10nm and 15nm sizes. Morphological changes in CdSe-hNPs have presented by describing the first stage melting in hollow semiconductor NPs. The thermal effect on the atomic arrangement has also examined by the cubic zinc blende-to-wurtzite transformation occurred during the melting in hNPs. MD results show that the inner shells of those with thin walls have begun to melt at lower temperatures due to the thickness of the NPs. The first stage melting, which resulted in the filling of the void within the particle, takes place almost at the same temperature for hNPs with the thick wall thickness. Then, the melting of the particles is completed at higher temperatures. The cubic diamond structure disappears with the collapse of the inner cavity, and the hcp structure begins to appear at later temperatures.

Abstract: In this work, the development of room-temperature solution-processed hybrid solar cells based on carbon nanotubes (CNT) - CdSe quantum dot (QD) hybrid material incorporated into a layer of conjugated polymer poly [2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′] dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], PCPDTBT, has been demonstrated. Incorporation of multi walled CNTs helps to improve the long-term efficiency of the solar cells in respect of power conversion efficiency (PCE) and short-circuit current density (Jsc) compared to QD only based devices. For the formation of the hybrid material hexadecylamine (HDA)/ trioctylphosphine oxide (TOPO) capped CdSe QDs were attached to CNTs by engineering the interface between CNTs and CdSe QDs by introducing thiol functional groups to CNTs. Initial PCE values of about 1.9 % under AM1.5G illumination have been achieved for this hybrid CNT-CdSe photovoltaic device. Furthermore, the long term stability of the photovoltaic performance of the devices was investigated and found superior to CdSe QD only based devices. About 90 % of the original PCE remained after storage in a glove box for almost one year without any further encapsulation. It is assumed that the improvement is mainly due to the thiol-functionalization of the CNT interface leading to a strong binding of CdSe QDs and a resulting preservation of the nanomorphology of the hybrid film over time.

Abstract: Different size of colloidal CdSe quantum dot (QD) was synthesized through a simple solvothermal route and their structural, morphological and optical properties were characterized with X-ray diffraction (XRD), transmission electron microscope (TEM), UV-visible absorption spectroscopy and fluorescence spectrometer. XRD and TEM measurement confirmed the formation of CdSe QDs. The red shift of absorption and fluorescence peaks indicated that the size of CdSe QDs increased with prolonging reaction time. The size of QDs varied from 2.2 nm to 3.4 nm by varying reaction time from 1 h to 7 h. The absorption spectra of CdSe/TiO₂ electrodes proved that the loading of CdSe QDs on TiO₂ can be greatly improved by MPA pretreatment. The effect of size of CdSe QDs on the performance of CdSe QDs sensitized solar cells was investigated. Due to the change of absorption range in the visible region and the conduction band shift for different size of CdSe, the photo-electric power conversion efficiency first increased and then decreased with increasing size of CdSe. The devices fabricated with 3.1 nm diameter CdSe nanoparticles exhibited the highest conversion efficiency of 0.70% under AM 1.5 G irradiation (100 mW cm⁻²).

Abstract: This essay employed the "successive ion layer adsorption and reaction (SILAR)"technology to form PbSe/CdSe core/shell.We use the Pbse/CdSe core/shell replaced PbSe nanocrystals and obtained one new quantum dot solar cells of the inorganic.This new solar cells constituted by the metal oxide films retain the photoelectric conversion efficiency of quantum dot solar cells.At the same time,the stability of the new solar cells is tremendously improved with the oxidation resistance of inorganic oxide.Finally,when J_sc=25.2mA/cm²and V_oc=0.36V ,we can conclude the conversion efficiency of the solar cell can be evaluated as 3.929%.

Abstract: Nanoparticles such as cadmium selenide (CdSe) have unique optical properties in term of band gap. These properties can be adjusted by controlling the size of nanoparticles. In this research we have synthesized different sizes of CdSe nanoparticles by controlling the reaction temperatures at 260 ^oC and 300 ^oC using a hot injection method. The as-synthesized CdSe nanoparticles were characterized using UV-visible spectroscopy and high resolution transmission electron microscope. From the UV-visible absorption spectra, the absorption peak of CdSe nanoparticles synthesis at growth temperature of 260 ^oC was 521 nm with estimated particle diameter of 2.57 nm, and for 300 ^oC the absorption peak was at 601 nm with estimated particle diameter of 4.63 nm. This indicates that the size of CdSe nanoparticles can be controlled by controlling the reaction temperature.