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TiO2 modified by Sm and catechol for photovoltaic use

Nanostructured titanium dioxide is known as a material with excellent physical and chemical properties, such as high specific surface area, high photo-activity, and environmental stability as well as low-cost synthesis. TiO2 exists in three different crystalline phases: anatase, rutile and brookite, but it was found that anatase (Eg ~ 3.2 eV) is more photo-active than other modifications. It has gathered much research for its application in solar energy, primarily as the electron transporting layer in perovskite and dye-sensitized solar cells. Furthermore, numerous studies were done with the aim to furthered improve optical properties of TiO2 e.g. by doping with other elements and by modification with different organic and inorganic substances. In this work, we studied the influence of doping with samarium and furthered modification with organic catechol to improve TiO2 morphology, structure, optical properties and photovoltaic performance. TiO2 samples doped with samarium were prepared by sol-gel syntheses, while further modification by catechol was obtained by immersing overnight in a solution of different concentration. The structure and morphology of nanostructured TiO2 doped with Sm and modified by catechol were studied using FEG-TEM Philips CM200-F. HAADF-DF and BF were used with the aim to study doping of the TiO2 and were performed using JEOL- ARM300. The thin layers of porous doped and modified TiO2 for photovoltaic application are prepared by sintering of the materials applied at the conducting glass substrates by blade casting. The morphology of the obtained layers was studied by HR-SEM Hitachi. Electron microscopy results were related to Raman spectroscopy measurements, while the optical properties are studied by UV-vis spectroscopy. The dye-sensitized solar cells solar cells were prepared using different types of doped and modified TiO2 as electron conductive layers. TEM measurements of doped as well as doped and additionally modified TiO2 samples indicated crystallite sizes smaller than 10 nm and strong agglomeration of the particles (Figure 1), which influenced the preparation of the thin layers. HAADF-DF measurements show successful doping of the TiO2 nanoparticles by Sm that are inbuilt substitutionary in the crystal lattice of TiO2 (Figure 2). The Raman spectroscopy measurements clearly indicated anatase structure of TiO2, but also bands characteristic for luminescence due to the Sm in crystal lattice were observed. The solar cell performances will be discussed in the view of structure and crystallite sizes of the starting TiO2 powder with different doping and modification as well as in the view of the morphology of the obtained electron conducting layers.

TiO2 ; samarium ; SEM ; TEM

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