Doping a TiO₂ Photoanode with Nb⁵⁺ to Enhance Transparency and Charge Collection Efficiency in Dye-Sensitized Solar Cells

The optoelectronic properties of our benchmark nanocrystalline anatase TiO2 photoanode were modified by means of aliovalent doping with Nb5+. Even for a low doping level, the charge collection efficiency can be noticeably improved as a result of a higher electron lifetime when using the heteroleptic Ru(+II) C101 dye. Particularly of interest, while this was only possible by adding additives in the electrolyte, the doping concentration allows tuning of the energetic of the trap state distribution; parameter particularly crucial for the injection rate and charge collection efficiency. This improvement brings the power conversion efficiency of a 7 μm thick transparent photoanode to 8.7% while intensifying the electrode’s transparency.