Influence of elevated radiative lifetime on efficiency of CdSe/CdTe Type II colloidal quantum dot based solar cells

Colloidal quantum dots (CQDs) are promising materials for solar cells because their optoelectronic properties are easily adjusted by control of their size, structure and composition. We present calculations of the band gap and radiative lifetime for varying core diameter and shell thickness of CdSe/CdTe core/shell Type II CQDs using a combination of single particle (2,6)-band k·pk·p and many-electron configuration interaction (CI) Hamiltonians. These calculations are validated by comparison with experimental absorption spectra and photoluminescence decay data. The results are then incorporated into a model of photovoltaic efficiency which demonstrates how the overall performance of a solar cell based on Type II CQDs is affected by changes in the core/shell geometry. The largest effect on photovoltaic efficiency is found to be due to the longer radiative lifetime produced by increasing the shell thickness

Plan de mejora para la disminución de la rotación en Movich corporativo

En este proyecto de grado tiene como fin encontrar un plan de mejora para la disminución de la rotación en empresas del sector hotelero, para mejorar la productividad de los compañeros, motivándolos de manera extrínseca o intrínseca, dentro de dicho documento estará el software E-Learning para capacitar a los empleados y de esta manera, que pueda ejercer un plan de carrera al interior de la organización, motivación por medio de las distintas alianzas generadas, todo esto para que los empleados encuentren un clima laboral afable a sus necesidades.In this degree project aims to find an improvement plan for the decrease of rotation in companies in the hotel sector, to improve the productivity of peers, motivating them in an extrinsic or intrinsic way, within said document will be the E-Learning software to train employees and in this way, that can exercise a career plan within the organization, motivation through the various alliances generated, all this so that employees find a working environment friendly to their needs.Administrador (a) de EmpresasPregrad

Quantized growth of semiconductor nanoparticles, investigation of aggregation dynamics and the growth kinetics

Doctor of PhilosophyDepartment of ChemistryViktor ChikanColloidal semiconductor nanoparticles will be important and practical next generation materials that can be cheaply manufactured. The objective of this project is to gain more inside into chemistry is used to control the formation and assembly of semiconductor nanoparticles (NPs). As a model system CdSe and CdTe nanoparticles are used in this work. The growth kinetics, aggregation dynamics, and heterogeneous growth of NPs by using novel tools such as; in-situ monitored fluorescence and absorption techniques, time-resolved and static fluorescence spectroscopy, TEM (transmission electron microscopy), and numerical simulations are studied. This study can be divided into the following four parts. The first part presents experimental observation of the quantized growth of CdTe quantum dots (QD). The high-temperature absorption spectra indicate the evolution of multiple peaks corresponding to various sizes of QDs. The observed aggregation is driven by dipole-dipole interaction of NPs. The second part is an investigation of the aggregation dynamics of magic-sized CdTe quantum dots and how this process can be controlled. It is shown that the growth kinetics of the QDs is very sensitive to the Cd/Te ratio. Cd-rich conditions form very different aggregation pattern due to the lack of formation of magic-sized nanoparticles. Simulations also suggest that the formation mechanism is mainly coalescence of the particles rather than the ‘neck formation’ within the CdTe aggregates. The next part investigates the growth of NPs in the presence of two distinctly sized NPs in the bimodal growth regime via numerical simulations. The bimodal distribution (or quantized Ostwald ripening) technique is found to be a slower process than the repeated injection technique to focus the size distribution of NPs. Slower growth will reduce inhomogeneity in a scaled-up production of NPs. The last part focuses on the effect of addition of doping on vii heterogeneous growth and the growth kinetics. The low temperature synthesis lacks the heterogeneous growth regime. However, as the temperature is increased to 120 0C, two different sizes emerge. Addition of In dopants seems to accelerate the growth kinetics and the magic sized NPs in the solution possess a negative anisotropy that is most likely due to supperlatice formation of magic-sized NPs

Growth and stability of ZnTe magic-size nanocrystals

synthetic method for ZnTe magic-sized clusters (MSCs) is reported, and the stability and growth kinetics of these clusters are investigated. Four distinct MSC families, with lowest-energy absorption peaks at 330, 354, 378, and 392 nm, are observed. The stability and growth kinetics of the MSCs are strongly influenced by the reaction temperature, precursor concentration, and nature of the ligands used as the coordinating solvent. High precursor concentrations result in faster growth and MSC formation at lower temperatures. Higher temperatures accelerate the growth kinetics and lead to a gradual shift from the stepwise MSC growth regime to a continuous growth regime. For temperatures above 260 °C, only continuous growth of nanocrystals is observed. The nature of the ligands also influences the stability and growth of ZnTe MSCs, which are formed with primary alkylamines as ligands, but not when trioctylphosphine, trioctylphosphine oxide, or trioctylamine are used as the sole ligands. This demonstrates the crucial role of ligands in the formation of stable ZnTe MSCs using colloidal synthetic methods. Under optimal synthetic conditions (200 °C, hexadecylamine as ligand, and suitable precursor concentrations), the method presented here allows the synthesis and isolation of a single MSC family absorbing at 330 nm