Probing the dye–semiconductor interface in dye-sensitized NiO solar cells

Abstract

The development of p-type dye-sensitized solar cells (p-DSSCs) offers an opportunity to assemble tandem photoelectrochemical solar cells with higher efficiencies than TiO2-based photoanodes, pioneered by O’Regan and Grätzel [Nature 353, 737–740 (1991)]. This paper describes an investigation into the behavior at the interfaces in p-DSSCs, using a series of BODIPY dyes, BOD1-3. The three dyes have different structural and electronic properties, which lead to different performances in p-DSSCs. We have applied photoelectron spectroscopy and transient absorption spectroscopy to rationalize these differences. The results show that the electronic orbitals of the dyes are appropriately aligned with the valence band of the NiO semiconductor to promote light-induced charge transfer, but charge-recombination is too fast for efficient dye regeneration by the electrolyte. We attribute this fast recombination, which limits the efficiency of the solar cells, to the electronic structure of the dye and the presence of Ni3+ recombination sites at the NiO surface.

Dye-sensitized solar cells strike back

“…668,688 The surface electronic states at the interface between NiO and a series of bodipy dyes have been studied by hard and soft XPS and the good overlap between the dye HOMO and semiconductor valence states was consistent with rapid light-induced charge transfer. 660 Recombination at the dye À /NiO + interface, however, is also fast, occurring on a picosecond to nanosecond time scale in simple dye systems such as bodipy and perylene. 660,715,716 Regeneration occurs from a nanosecond up to microsecond time scale.…”

“…660 Recombination at the dye À /NiO + interface, however, is also fast, occurring on a picosecond to nanosecond time scale in simple dye systems such as bodipy and perylene. 660,715,716 Regeneration occurs from a nanosecond up to microsecond time scale. Competition between recombination and regeneration is responsible for the poor efficiency for p-type DSCs.…”

“…These are relatively straightforward to synthesize and simple modifications to the structure can be made to tune the absorption and emission wavelengths across the visible spectrum. 660 The performance of bodipy dyes anchored through benzoic acid at the meso position is quite low, but push–pull bodipy dyes with a triphenylamine donor linked through a thiophene spacer to the bodipy chromophore perform much better ( e.g. bodipy-6 PCE = ca.…”

NiO/ZrO2 nanocomposites as photocathodes of tandem DSCs with higher photoconversion efficiency with respect to parent single-photoelectrode p-DSCs

“…30,[52][53][54] For the last approach it has been found that the thermal treatment has the advantage of increasing the optical transparency of the NiO film, but it also brings about a significant diminution of the number of surface sites for dye-anchoring. 51,55 An efficacious way of passivating the surface of NiO is the addition of CDCA either in the electrolyte of the p-DSC, 30 or in the dyeing solution of NiO. 57 This is because CDCA reacts with the Ni(III) centres and renders them totally inactive towards recombination.…”

The degree of electron itinerancy and shell closing in the core-ionized state of transition metals probed by Auger-photoelectron coincidence spectroscopy

“…The necessity of small and still powerful electronic devices requires a deeper understanding of physical effects especially affecting the electronic properties of solid state materials. Especially 3d metals are among the most widely used for engineering purposes [1][2][3][4][5] . The 3d metals and their alloys cover a wide range of electronic properties such as semiconductors (Cu 2 O), superconductors (cuprates) or metal to insulator transitions in e.g.…”