No abstract

We have proposed to use a special electrochemical regime to introduce a preferable grain size into the entirely porosified Si material. This periodic pulse electrochemical regime permits layering of the entire porosified film and defines its preferable partition in the post anodization mechanical treatment. Thus, a preferable grain size is “hidden” in the grown porSi film and is revealed only under additional mechanical treatment like milling. The pore dimension and total porosity are controlled by applied current density at the work pulse and prefabricated (hidden) grain size is introduced during an application of the cut or/and relaxation pulses. We have applied a described procedure to produce a sub‐micrometric grain porSi powder and report results on SEM analysis of the material fabricated in different pulse regimes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

No abstract

DC/DC converters are widely used in photovoltaic (PV) systems to maximize the power drained from solar panels. As the power generated by a PV panel depends on the temperature and irradiance level, a converter needs to constantly modify its input resistance to remain at the maximum power point (MPP). The input resistance of a converter can be described by a simple equation that includes the converter load resistance and the duty cycle of the switching signal. The equation is sufficient for an ideal converter but can lead to incorrect results for a real converter, which naturally features some parasitic resistances. The goal of this study is to evaluate how the parasitic resistances of a converter influence its input resistance and if they are relevant in terms of MPPT system operation.

No abstract

No abstract

In recent years, In 2 S 3 thin films were widely used as buffer/window layer in thin film solar cells as an alternative to toxic CdS. In the present work, we demonstrate the potential of surface photovoltage spectroscopy for estimation of minority carrier diffusion length, band gap energy and refractive index of thermally evaporated In 2 S 3 thin films. The estimated minority carrier diffusion length of In 2 S 3 thin films from SPV measurements were 0.112 μm and 0.052 μm for films annealed at 250 and 300 °C respectively.

Initially H-terminated and therefore hydrophobic surface of electrochemically prepared luminescent porous silicon (PSi) powder was transformed to the hydrophilic one by means of surface modification by undecylenic acid. Physical adsorption of undecylenic acid as a non-ionic surfactant and its chemical binding through C[triple bond]C bond opening and Si-C bond formation were applied as two different methods of PSi surface modification, physical and chemical modification, respectively. Luminescence of aqueous suspensions of the both types of modified PSi powders in merely water and in simulated body fluid physiological electrolyte was measured as a function of time. Many-fold (up to 20 times) building-up of the luminescence intensity was observed for PSi aqueous suspensions during the first few days, the growth was followed by a slower (a week and more) luminescence intensity decay. As it is evidenced by FTIR spectra and SEM images, the effect of the luminescence growth and decay of PSi suspension in water can be in part attributed to the PSi surface oxidation accompanied by its dissolution and de-aggregation of large PSi particles. It is concluded also from the experiments on PSi luminescence reversible quenching by O2 that SiO-related surface states with the excitation energy about 2.2 eV are formed during water-assisted oxidation of Si nanocrystal surface. An appearance of a large number of such surface states can be also responsible for the observed PSi luminescence building-up.