In this study, the heterogeneous growth of CdSe nanoparticles is reported by using in situ fluorescence spectroscopy. In the heterogeneous growth regime, nanoparticles with well-defined and very different sizes can coexist in the solution. The average size and size distribution of the nanoparticles is primarily not controlled by the usual focusing-defocusing (Ostwald ripening) of particles, rather by the formation of "magic" sized particles. In these studies, the effects of indium doping from indium chloride on the growth kinetics, size, size distribution, as well as the quantum yield of the various particles in the growth solution is investigated. Specifically, it is shown that the indium atoms accelerate the dissolution of the magic sized CdSe nanoparticles, while the chloride ions seem to stabilize the magic size particles. The present result will help to improve the understanding of how a dopant atom can affect the growth kinetics of semiconductor nanoparticles.

Controlling conductivity via doping in semiconductor quantum dots is an important part of nanoparticle research. In this report, doping of CdSe quantum dots with indium and tin is explored. High-resolution nanoprobing confirms the presence of indium and tin in the particles and the inclusion of indium into the particles without forming a separate phase. The tin doped CdSe samples show preferential adsorption of tin in quantum dots from the solution during synthesis while incorporation of indium is somewhat statistical. In agreement with the expected n-type behavior, the photoluminescence (PL) of both indium and tin doped samples exhibits a significantly steeper temperature dependence, compared to undoped CdSe quantum dots. Comparison of theory and experimental data suggests that the approximate locations of the dopants levels are at 280 and 100 meV below the conduction band edge of the indium and tin doped quantum dots, respectively. The relative temperature dependent Stokes shifts of the doped samples are larger than those of the undoped sample, suggesting that the electron is backfilling the lowest unoccupied quantum dots levels. The oxidized doped samples exhibit increased polarized band-edge emission. The likely explanation of the polarized emission is that trapping times are fast in the oxidized doped samples compared to the undoped samples.

Developing electronic doping of colloidal quantum dots is important for basic science and technology. In this article, the doping of colloidal CdSe quantum dots with gallium atoms is reported. Gallium doping of CdSe quantum dots produces important changes in electronic and optical properties of the material. The gallium doping shows a significant impact on the growth kinetics of quantum dots, which reveals important clues about the mechanism of the gallium dopant incorporation into the CdSe. The results show that the gallium doping significantly impacts the conductivity of CdSe thin film made of the quantum dots as well as the photoluminescence and chemical reactivity of the quantum dots, in agreement with the expected ntype character.

Colloidal CdSe quantum dots show great promise for fabrication of hybrid solar cells with enhanced power conversion efficiency. Here, we demonstrate that gallium-, indium-, tin-doped CdSe quantum dots show significantly improved conductivity and charge carrier density, and also temperature dependent behavior. Furthermore, the doped CdSe hybrid solar cells greatly enhance photocurrent and photovoltage, in which the gallium doped CdSe quantum dots and P3HT bi-layer heterojunction solar cells leads to a maximum power conversion efficiency of 2.0% at elevated temperatures under AM 1.5 solar illumination. All the doped samples exhibit inverted temperature dependent power conversion of the photovoltaic cells, which could be effectively utilized in solar concentrators. The approach presented can be applied to a wide range of doped quantum dots and polymer hybrids and is compatible with solution processing, thereby offering a general tactic for improving the efficiency of quantum dot based solar cells.The so called 3rd generation solar cells have been the interest of the scientific community with a promise of providing cheap and efficient photovoltaic devices. 1-4 One of the 3rd generation solar cell concepts depends on a combination of inorganic and organic photosensitizers. 5-8 The inorganic components can consist of quantum confined semiconductor structures 3, 9 (nanoparticle, nanorod, tetrapods) that are synthesized via colloidal route combined with conductive polymers such as P3HT. 10, 11 Varying the composition, size and shape of the inorganic component these photovoltaic cells allows capturing and utilizing photons from different parts from the solar output. While these solar cells are proven to be functional, it is difficult to manufacture them with high overall power conversion efficiencies; therefore, research needs to focus on concepts that can identify components that are responsible for the lack of improvements.Among the quantum dot (QD) materials, CdSe QDs received significant attention in this quest of producing efficient solar cells. Although CdSe is not a sustainable material, it provides a platform to study many different effects associated with the construction of polymer/inorganic solar cells. 3 In addition, the bandgap of colloidal CdSe QDs (2.6-1.7 eV) overlaps reasonably well with the solar output to capture large portion of the sunlight's energy. There are several reports that show P3HT/CdSe QDs solar cells provide somewhat efficient power conversion efficiencies in the few percent range. 9, 12-25 Recently, Zhou et al. have reached 5.3% record power conversion efficiency in PCPDTBT: CdSe device as a result of removal of trap sites upon the ethanedithiol 10.1149/06615.0001ecst ©The Electrochemical Society ECS Transactions, 66 (15) 1-8 (2015) 1 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 137.122.8.73 Downloaded on 2015-08-06 to IP