Stability and photodegradation of phthalocyanines and hematoporphyrin doped PMMA as solar concentrators

Luminescent solar concentrator samples using polymethylmethacrylate (PMMA) as the matrix with phthalocyanine, nickel-phthalocyanine and hematoporphyrin IX dichloride laser dyes were prepared by a casting method. Optical absorption measurements were carried out at room temperature across the 200–900 nm wavelength region both before and after the samples were exposed to sunlight for two weeks. The degradation of PMMA–dye samples, measured by absorption, was found to obey a first-order kinetic equation. Values of the optical band gaps (Eg) have been obtained for the direct allowed transitions before and after the samples were exposed to sunlight. The tail width of localized states in the band gap (Eu) was calculated from Urbach’s formula. Photodegradation studies revealed that the phthalocyanine dye systems are the most stable. Emission spectra and quantum efficiency were also investigated, and phthalocyanine dyes were shown to have a lower Stokes shift and a higher fluorescence quantum yield (Qf) than the hematoporphyrin IX dichloride. Collectively, these results suggest that PMMA doped with phthalocyanines provide the better system for use in fluorescent solar collector systems. 2006 Published by Elsevier Ltd