Solar Energy, Vol.81, No.9, 1159-1165, 2007
Quantum dot containing nanocomposite thin films for photoluminescent solar concentrators
Silicon oxide films containing US quantum dots have been deposited on glass substrates by a sol-gel dip-coating process. Hereby the US nanocrystals are grown during the thermal annealing step following the dip-coating procedure. Total hemispherical transmittance and reflectance measurements were carried out by means of a spectrophotometer coupled to an integrating sphere. For CdS-rich films, an absorption edge at photon energies in the vicinity of the band gap value of bulk US is observed. For lower US concentrations, the absorption edge shifts to higher photon energies, as expected for increasing quantum confinement. The samples show visible photoluminescence which is concentrated by total internal reflection and emitted at the edges of the substrate. The edge emission has been characterized by angle-dependent photoluminescent (PL) spectroscopy. Information on the lateral energy transport within the sample can be extracted from spectra obtained under spatial variation of the spot of excitation. The color of the photoluminescence can be tuned by varying the annealing temperature which governs crystal growth and thus the cluster size distribution. The characteristic features observed in the PL spectra clearly exhibit a blueshift for lower annealing temperatures, confirming the presence of quantum size effects. Advantages of the proposed concept of quantum dot containing coatings on glass panes for photoluminescent solar concentrators are the high potential for low-cost fabrication on the large scale and the suitability for architectural integration. (c) 2007 Elsevier Ltd. All rights reserved.
Keywords:fluorescent planar solar concentrators;quantum dots;CdS nanocrystals;quantum size effects;nanocomposite materials;sol-gel dip-coating;thin film technology;photovoltaic cells