Doping titania with rare-earth metals improves the photoconversion efficiency (PCE) of dye sensitized solar cells (DSSCs). In most reported cases, the overall cell quality is not optimal, making it unclear what role the rare earth oxide metal plays in the improvement, if any. Here we incorporate < 100 nm diameter nanoparticles of neodymium and erbium oxide into titania films and test their performance in high quality DSSCs. The doping level for optimized cells is 2.0% and 1.0% for neodymium oxide and erbium oxide by weight, respectively. This results in a 5 to 10% increase in PCE for the rare earth oxide doped DSSCs relative to undoped DSSCs, with erbium oxide being the best. The rare-earth metal-doped films exhibit a 20-25% larger dye loading and the loading was maximum at the same doping levels where the PCE was maximum, showing this is a big contributor to the improvement. The surface area is larger with rare-earth doped titania as determined by atomic force microscopy and BET analysis, explaining the higher dye loading. The cell impedance is lower with rare-earth doped samples, showing that the rare-earth metal oxide also facilitates electron transport through the mesoporous titania, improving the collection efficiency of the photoexcited electrons. (C) 2018 The Electrochemical Society.