Fabrication and performance of nanoporous TiO2/SnO2 electrodes with a half hollow sphere structure for dye sensitized solar cells

The incorporation of nano-crystalline semiconductors with novel kinds of ordered microstructure is a very important area of research in the field of dye sensitized solar cells. A sol–gel method involving hydrolysis of titanium isopropoxide was used to form TiO₂ nanoparticles on the surface of SiO₂ spheres. In this process, 1, 5, or 10 wt% of SnCl₂.2H₂O was added to the sol–gel solution. To prepare TiO₂/SnO₂ nanoparticles with a half hollow sphere structure, SiO₂ was removed with NaOH solution. The crystal phase, crystal shape, and surface properties of the metal oxide nanocrystals were studied by x-ray diffraction and scanning electron microscopy. The photovoltaic performance of the TiO₂/SnO₂ nanoparticles with half hollow sphere structures was measured. The dye sensitized solar cell using nanoporous TiO₂ as electrode materials exhibits an overall conversion efficiency of 7.36% with a light intensity of 100 mW/cm². The short circuit photocurrent (I_sc), open circuit photovoltage (V_oc), and conversion efficiency (η) of these solar cells were improved over conventional materials.     

Toward sustainable energy: photocatalysis of Cr-doped TiO<Subscript>2</Subscript>: 1. electronic structure

The present chain of five papers considers the concept of defect engineering in processing TiO₂-based photosensitive semiconductors for solar-to-chemical energy conversion. The papers report the effect of chromium on the key performance-related properties of polycrystalline TiO₂ (rutile), including (i) electronic structure, (ii) chromium-related photocatalytic properties, (iii) oxygen-related photocatalytic properties, (iv) electrochemical coupling and (v) surface versus bulk properties. The present work reports the effect of chromium on defect disorder and the related electronic structure of TiO₂, including the band gap and mid-gap energy levels. It is shown that chromium incorporation into the TiO₂ lattice results in a decrease of the band gap from 3.04 eV for pure TiO₂ to 1.4 and 1.3 eV, for Cr-doped TiO₂ (1.365 at% Cr) after annealing at 1373 K in the gas phase of controlled oxygen activity, 21 kPa and 10^?10 Pa, respectively. The optical properties determined using the ultraviolet-vis spectroscopy (in the reflectance mode) indicate that chromium incorporation results in the formation of mid-band energy levels. In this work, we show that chromium at and above the concentrations levels of 0.04 and 0.376 at% results in the formation of acceptor-type energy levels at 0.57 and 1.16 eV (above the valence band), respectively, which are related to tri-valent chromium in titanium sites and titanium vacancies, respectively. Application of well-defined protocol leads to the determination of data that are well reproducible. The new insight involves the determination of the band gap of TiO₂ processed in the gas phase of controlled oxygen activity.

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Investigations of the defect structure of CdS single crystals and explanation of the exciton lines shift

In this paper an influence of the defect structure of CdS crystal on the exciton line shift has been investigated. It was proved that the exciton line shift towards higher energies is connected with variations of the lattice constant caused by zinc impurities. CdS crystals after Zn ions implantation do not reveal the exciton line shift and only broadening of these lines occurs due to the strain field existing in crystal lattice.     

The defect structure of CdS crystals heavy doped with Cu,Se. and Zn atoms

In this paper the defect structure of CdS crystals doped with Cu, Se and Zn atoms has been investigated. There were used two X-ray methods: the oscillating slit and oscillating film methods. CdS crystals were obtained from the melt under pressure of Se and Zn 0.5, 0.75, 1% wt and Cu 0.25, 0.5, 0.75, 1% wt in relation to CdS crystals. It was proved that high doping damages the structure of CdS crystals and that especially Cu impurity much more disturbs the crystal lattice than Zn one. Se atoms cause rather small deformation of crystal and increase the lattice constant, this being connected with decreasing of energy gap.