Study of dye sensitized solar cells photoelectrodes consisting of nanostructures

An important element that allows the dye sensitized solar cells (DSSC) photovoltaic assemblies to achieve high efficiency is the photoelectrode. In this kind of solar devices photoanode is mostly in the form of a meso-porous oxide layer composed of nanostructures with attached dye molecules through bonds between the hydroxyl group of the oxide material and the carboxylic group in the dye structure. It is responsible for the separation of charge carriers, which plays the most important role in the photovoltaic effect.

The used dyes should be characterized by: higher dye excitation energy than the edge of the oxide semiconductor, the wide absorption spectrum, presence of groups that allow permanent bonding to the surface, resistance to photodegradation and photocorrosion, lower level of the basic state than the redox potential of the electrolyte allowing dye regeneration, thermal and electrochemical stability. Nowadays the most commonly used dyes are ruthenium, osmium, copper, iridium complexes as well as porphyrins and phthalocyanines.

The work involved the production of two types of photoelectrodes, containing TiO₂ nanoparticles and TiO₂ nanoparticle/nanowire. The nanowires of TiO₂ have been produced with use electrospinning method. The both photoelectrodes have been obtained by screen printing method ensuring dimensional accuracy and repeatability of production.

In order to determine the properties of photoanodes, topographical studies were performed using atomic force microscope (AFM), allowing through RMS Ra roughness coefficients determination to quantify of surface of the electrodes, qualitative studies of chemical composition using Energy Dispersive Spectrometer (EDS), X-ray structural studies, and investigations of optical properties in the wavelength range 200 to 800 nm.

The I-V characteristics of dye sensitized solar cells were measured using PV Test Solutions Tadeusz Zdanowicz Solar Cell I-V Tracer System and Keithley 2410 source meter under Standard Test Conditions (AM 1.5, 100 W/m2).

The research confirmed that the use of selected method of producing TiO₂ nanowires and the method of photoelectrode production allows to obtain a large specific surface area as well as homogeneity of the electrodes. Investigations of optical properties indicate good absorption of the dye used to the semiconductor TiO₂ layer, both composed of nanoparticles and the nanoparticle/nanowire system.

Obtained cell efficiency results at 4.5-5% make photovoltaic structures promising from the point of view of further development and further application.