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

Abstract

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.

Fluorine- and Niobium-Doped TiO2: Chemical and Spectroscopic Properties of Polycrystalline n-Type-Doped Anatase

“…If theoretical calculations does not allow a choice between these two solutions, the data related to the oxygen spin density and those here reported (position of the Fermi level), clearly point to a delocalized model. The excess electron centers detected by EPR, Fig 3, are thus responsible of the conduction of the solid which has been measured for Nb-TiO 2 materials and resulted to be higher than that of pure titania 24 . The fact that no optical absorption is observed for the as prepared samples despite the presence of Ti 3+ centers (Fig.…”

“…The co-doped systems can be described by a combination of the two previous formulas. Another compensation mechanism based on the formation of Ti 4+ vacancies, which has been proposed based on conductivity measurements 24 , cannot in principle be excluded and will be discussed in Section 4. The features of the EPR spectra, however, unambiguously indicate that at least a fraction of the dopant (F or Nb) releases excess electrons into the solid producing donor Ti 3+ centres that modify therefore the electronic structure of the solid itself.…”

A Review on Current Status of Stability and Knowledge on Liquid Electrolyte-Based Dye-Sensitized Solar Cells

“…It also allows charge compensation mechanism to maintain a low concentration carriers [75]. We can list a series of hypervalent cations which have been successfully incorporated into the anatase crystal structure: W 6+ [76], Nb 5+ [77][78][79][80] [89]. The common observation is that hypervalent doping affects the energy of acceptor trap states.…”

Enhancing Electron Injection in Dye‐Sensitized Solar Cells by Adopting W6+‐Doped TiO2 Nanowires: A Theoretical Study

“…[13] In addition, nitrogen as a dopant in TiO 2 was found to be harmful to the stability of batteries. Fortunately, doping with transition-metal ions (e.g., V 4+/5+ , [14] Fe 2+ , [15] Ce 4+ , [16] Zn 2+ , [17] Zr 4+ , [18] Nb 5+ , [19] Ta 5+ , [20] Cr 3+/4+ , [21] and W 6+ [7a] ) in TiO 2 has been found to shift the CB edge down and to change the electron-injection driving force of sensitizers. Doping with transition metals is also considered to be a feasible strategy to improve the value of J sc and the IPCE.…”