We present a sol-gel process which is used to prepare thin titanium dioxide nanoparticle layers by spin-coating or doctor-blading techniques. After being sensitized with a dye, the films are used for the transport of electrons in photoelectrochemical solar cells. The titanium dioxide particles have diameters of about 100 nm. A comparison with screen-printed layers consisting of particles with a typical size of 25 nm shows that the power conversion efficiencies of the cells reach identical levels. Thus, we can show that a large internal surface of the nanocrystalline layers, which is one prerequisite for a good solar cell performance, can only be achieved by adjusting the respective size of the nanoparticles. The coating and heating processes, and the obtained crystal structure of titanium dioxide also play a major part in the preparation of highly efficient devices.