Browsing by Author "Saarinen, Jaakko"

Now showing 1 - 1 of 1

Manufacturing and characterization of compacted and low-temperature-sintered nanostructured titanium dioxide films for dye-sensitized solar cells
(2004) Saarinen, Jaakko
Helsinki University of Technology | Master's thesis
The dye-sensitized solar cell (DSSC) is an electrochemical solar cell. The absorption of light takes place in dye molecules adsorbed as a monolayer on a nanostructured wide band-gap semiconductor electrode which is usually titanium dioxide. To date, the efficiency record for a DSSC is ca 11 %. The most efficient photo electrodes are obtained by sintering at high temperatures requiring the use of glass substrates. The current research trend is to replace the costly glass by inexpensive plastic substrates by developing compaction and low-temperature sintering (at 150°C or below) techniques to deposit the titanium dioxide. The ultimate goal is to produce both the photo electrode and the counter electrode by compaction in continuous roll-to-roll processes. This thesis starts with an introduction to the characteristics of solar cells and the basic technology behind the DSSC. This is followed by discussing the phenomenology of compaction and sintering. Nanocrystalline TiO2 is a hard ceramic material, which cannot be compacted easily to high densities. If the starting powder is additionally agglomerated, the resulting product has high porosity. Also, sintering below 550°C does not activate significant densification in the powder giving a porous product with strong interparticle contacts. Titanium dioxide thin films were prepared by compaction and low-temperature sintering both on glass and plastic substrates. Characterization of the titanium dioxide materials and films utilized in the photo electrode of the DSSC was performed by light and electron microscopy, thermal analysis and current-voltage performance measurements of whole solar cells using a solar simulator at illumination corresponding to 1000 W /m2 and AM 1.5G spectrum. Compaction resulted in stable and thick TiO2 films with good performance, whereas the stability of low-temperature sintered films was poor and thick films could not be prepared. Their performance was nonetheless good taking their thinness into account. The best efficiencies obtained for DSSCs with compacted TiO2 films were 3.3 % and 1.7 % on glass and plastic substrates, respectively. Correspondingly, the efficiencies obtained by low-temperature sintering were 2.7 % and 1.7 % on glass and plastic substrates, respectively.