Defects in Local Atomic Structure of ZnO Films Sensitized with Tinto and Mangrove Organic Dyes

In this work, the dye/ZnO complex was prepared, using natural dyes extracted from the red tree (Haematoxylum campechianum L.) and mangrove tree (Rhizophora Mangle), with a concentration of 5 x 10-3 M, impregnation time of 2 and 6 h, using a mixture of ethanol-water and ethanol as solvents. The ZnO particles were obtained by sol gel method and deposited on Corning glass by the doctor blade technique. X-ray diffraction indicates that these particles belong to the wurtzite-type hexagonal crystalline structure. Anthraquinone and anthocyanin molecules were identified in the natural dyes used. The results of the Fourier Transform Infrared Spectroscopy of the complexes show the band associated with the functional group of the carboxyls, which represents evidence of the presence of the dyes in the semiconductor. X-ray absorption spectroscopy shows changes in the local environment around the Zn atoms. Both dyes introduce a greater quantity of electrons in the unoccupied p states of Zn. The simulation developed and the analysis of the EXAFS signals show the formation of new bonds between Zn and O with dye atoms thus reducing the Zn O and Zn-Zn bond lengths. Also, the distribution of the bonds of the neighbors closest to the Zn, in the ZnO matrix, is modified due to the generation of vacancies of O and Zn. These results imply that the obtained dyes can effectively be used as photosensitizers in ZnO-based solar cells.