Abstract
Zinc oxide nanoparticles with different sizes and shapes have been synthesized in polyol using a bottom-up approach. We have studied the scale-up of the process to massively produce high quality nanoparticles of controlled size and shape. The scale-up strategy required the effective mixing of reagents using either axial or radial mixing configurations and was experimentally validated by comparing structural properties of particles obtained in a small and a large size reactor. In addition, the flow patterns in these reactors have been calculated using three-dimensional turbulent computational fluid dynamics (CFD) simulations. Our results indicate a strong connection between the flow patterns, as obtained by CFD simulations, and the size and shape of the particles. Actually, our pilot scale reactor allowed producing sample aliquots of ~50 grams with nanoparticle sizes ranging from 8 nm to 600 nm and aspect ratio varying from 1 (nanospheres) to 20 (nanorods). After their synthesis, these two nanoparticle classes have been tested as building blocks in D149-dye-sensitized solar cell (DSSC). The measured power conversion efficiency (PCE) was 4.66% for nanorods shaped particles and 4.21% for nanospheres. These values were significantly higher than the 3.90% PCE obtained with commercial Degussa VP20 ZnO nanoparticles.
Highlights
There is a crucial need to develop reliable growth techniques capable of yielding high purity semiconducting nanomaterials with controlled size and morphology in industrial quantities to incorporate them in solar energy devices
The measurements of individual nanoparticle size were performed from transmission electron microscopy (TEM) pictures coupled with the Image J image analysis software
The X-ray diffraction (XRD) crystallite sizes, calculated from Scherrer’s equation, are similar to those obtained from TEM analysis, indicating that the nanoparticles are fairly single crystalline
Summary
There is a crucial need to develop reliable growth techniques capable of yielding high purity semiconducting nanomaterials with controlled size and morphology in industrial quantities to incorporate them in solar energy devices. Due to their chelating properties, polyols can play a role in coordinating solvents, complexants, and surfactants that adsorb on the elementary particle surface during growth, preventing their agglomeration These materials allow two competitive chemical reactions to occur: reduction and forced hydrolysis. This method already permitted the rigorous control of the size and shape of such nanomaterials as zinc oxide nanoparticles via adjustment of the reaction stoichiometry, i.e., hydrolysis ratio and basicity [31] Other parameters such as the efficiency of mixing reagents, could affect the particle size distribution, especially in highly viscous polyol media and fast and irreversible precipitation reactions. This work presents a scaling-up strategy to produce zinc oxide semi-conducting nanoparticles with controlled properties by the polyol synthesis process. Their power conversion efficiencies were measured and compared with cells based on a commercial ZnO powder
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