Solar-to-Electric Performance Enhancement by Titanium Oxide Nanoparticles Coated with Porous Yttrium Oxide for Dye-Sensitized Solar Cells

TiO 2 –Y 2 O 3 core–shell nanoparticles for dye-sensitized solar cells (DSSCs) have been fabricated by a solvothermal technique. The heterostructure of TiO 2 nanoparticles coated with porous Y 2 O 3 is confirmed with transmission electron microscopy. The bonding of the Y 2 O 3 coating on the TiO 2 surface is quantitatively analyzed in terms of the Lifshitz–van der Waals and electrostatic contributions to the surface free energy of the particles. TiO 2 and Y 2 O 3 constitute a core–shell heterojunction because the Fermi levels merge; this increases the open-circuit voltage. Higher recombination resistances are obtained in DSSCs with porous Y 2 O 3 -coated TiO 2 compared with those in the reference cells, indicating “backscattering” inhibition of the porous Y 2 O 3 barrier on TiO 2 nanoparticles. Moreover, smaller transport resistances and longer electron lifetimes are achieved in DSSCs with TiO 2 –Y 2 O 3 core–shell nanoparticles. Compared with a reference cell, the V OC of a DSSC with a partial Y 2 O 3 coating on the surface of the TiO 2 nanoparticles improves from 683 to 738 mV and the J sc from 14.15 to 15.35 mA·cm –2, whereas the conversion efficiency increases by 15.2%.