Dye-sensitized solar cell fabricated by electrostatic layer-by-layer assembly of amphoteric TiO2 nanoparticles

Nanocrystalline TiO2 amphoteric colloidal charged particles and polyelectrolytes have been used to fabricate a dye-sensitized solar cell. Two weak polyelectrolytes, poly(allylamine hydrochloride) and poly(acrylic acid), and two strong polyelectrolytes, poly(dimethyldiallylammonium chloride) (PDAC) and poly(sodium 4-styrenesulfonate), have been utilized to assemble polyion/TiO2 nanocomposite multilayered films by the electrostatic layer-by-layer deposition technique. The layer-by-layer assembly of the TiO2 nanoparticles proceeds linearly as shown by sequential UV-vis absorption and thickness measurements. The morphology of these assemblies was characterized using atomic force microscopy. The nanoporous polyion/TiO2 films were sintered and used as working electrodes for cis-di(thiocyanato)-NN-bis(2,2'-bipyridyldicarboxylate)-ruthenium(II) (N3) sensitized solar cells. I-V characteristics of the solar cells made by the calcinated polyelectrolyte/TiO2 electrodes show several;interesting results. (i) The short-circuit current does not linearly increase with the thickness of the TiO2 electrode, even though the adsorption behavior of the N3 dye shows a linear increase. (ii) The precursor polyelectrolytes used to assemble TiO2 play a major role in the photovoltaic performance of the solar cells. Thermogravimetric analysis studies show that the thermal stability of the polyelectrolytes may have a direct effect on the overall device efficiency. (iii) The photovoltaic performance of these solar cells is comparable to that of cells made by other methods such as spin casting, the layer-by-layer technique offers unsurpassed control in manipulating the final device thickness. An efficiency of 7.2% was obtained for the solar cell made from PDAC/TiO2 (200 bilayers) precursor film, under 1 sun at simulated Air Mass 1.5 direct irradiation.