Via sol–gel route, we synthesized Nb-doped TiO2
nanoparticles, with
doping rates up to 6 mol%. The size of nanoparticles ranging from 1.8 to
2.4 nm and anatase crystalline phase was characterized by XRD. All the
samples were well dispersed in alcohol solvent due to organic ligands
attached to TiO2
nanoparticles, and thus uniform thin films with
subnanometer scale roughness could be obtained. Ellipsometry analyses on thin films revealed that the refractive indices were increased by
~20% by thermal sintering. Uniform thin films of Nb-doped TiO2
nanoparticles were utilized as HBL of OSC, and improved PCE by Nb doping
was confirmed by single cell performance measurements.