Effects of TiO2 nanoparticle polymorphism on dye-sensitized solar cell photovoltaic properties

We present a joined experimental and theoretical investigation of the TiO2 polymorphism effects on dye-sensitized solar cells (DSSCs) photovoltaic properties. TiO2 nanoparticles of pure anatase, pure rutile and pure brookite stabilized phases with various sizes have been prepared by solution sol–gel approaches in order to evaluate their properties in photovoltaic devices. For a valuable comparison, these various nanoparticles have been used to construct identical solar cells. Their properties have been thoroughly estimated and analysed by J–V curves and impedance spectroscopy measurements along with first-principles calculations based on the density functional theory (DFT) under the B3LYP approximation. In the light of DFT calculations, the open circuit voltage (Voc) behavior of the solar cells is mainly explained by the dependency of the bottom of the conduction band position on the TiO2 phase. Quantifications of electron lifetimes, transfer times, diffusion coefficients (Deff) in the various polymorph TiO2 photoanodes are also of particular importance for explaining the photovoltaic properties of the different DSSCs. We have notably found a conductivity and Deff order being rutile < brookite < anatase. The comparison of anatase and brookite based-cells shows that the latter phase is very interesting for the considered application.

► Nanoparticles of the three main stable phases of TiO2 have been synthesized.
► Pure phase TiO2 porous films have been prepared and evaluated for the fabrication of dye-sensitized solar cells.
► DFT calculations have permitted to understand the cell Voc behavior of the polymorphs.
► Important cell functioning parameters have been determined by impedance spectroscopy and compared for the main TiO2 phases.