Síntese e funcionalização de pontos quânticos de CdSe para aplicação em dispositivos fotovoltaicos

Abstract

This master's thesis approaches the synthesis and passivation of cadmium selenide (CdSe) quantum dots (QDs) with 3-mercaptopropionic acid (MPA), thioglycolic acid (TGA) and beta-alanine (β-alanine) for application in hybrid photovoltaic devices with FTO/TiO2/P3HT:PCBM:CdSe/Ag structure. The text presents an introduction about the current scenario of electric power generation and emphasizes the evolution of new technologies that use renewable sources for power generation. CdSe QDs were synthesized via hot injection and were optically characterized by UV-Vis spectrophotometry and photoluminescence spectrometry, which indicated activity in the visible region of the electromagnetic spectrum. The passivation of the QDs with the different ligands modified the photoluminescence spectra of the nanocrystals regarding the emission intensities related to radiative and non-radiative transitions and the position of the nanoparticle’s emission peak. Measurements of optical absorption, photoluminescence, X-ray diffraction, profilometry and sheet resistance were carried out for optical, structural, morphological and electrical characterization of compact and mesoporous layers of titanium dioxide (TiO2), CdSe QDs, and poly(3-hexylthiophene 2,5-diyl):Phenyl-C61-butyric acid methyl ester (P3HT:PCBM) blend layers deposited by spin coating and silver (Ag) electrodes obtained by thermal evaporation. Finally, measurements of current density × voltage (J×V) were employed for electrical characterization of the built photovoltaic devices. The hybrid photovoltaic cells based on P3HT:PCBM:CdSe produced in this work presented efficiencies between 0.15% and 0.21%, depending on the ligand anchored to the surface of the QDs. The electrical characterizations of the built solar cells indicated enhancements in the extraction and mobility of charge carriers when CdSe QDs passivated with the different ligands were incorporated into the P3HT:PCBM blend in the active layer of the devices. The union of the organic blend (P3HT:PCBM) with the inorganic semiconductor nanocrystals (CdSe QDs) in the active layer of the cells improved charge mobility and reduced losses due to recombination compared to cells without the incorporation of the QDs, results that benefit the conversion of solar energy into electrical energy.