Deposition of a Thin Film of TiO_x from a Titanium Metal Target as Novel Blocking Layers at Conducting Glass/TiO₂ Interfaces in Ionic Liquid Mesoscopic TiO₂ Dye-Sensitized Solar Cells

Abstract

In dye-sensitized TiO2 solar cells, charge recombination processes at interfaces between fluorine-doped tin oxide (FTO), TiO2, dye, and electrolyte play an important role in limiting the photon-to-electron conversion efficiency. From this point of view, a high work function material such as titanium deposited by sputtering on FTO has been investigated as an effective blocking layer for preventing electron leakage from FTO without influencing electron injection. X-ray photoelectron spectroscopy analysis indicates that different species of Ti (Ti4+, Ti3+, Ti2+, and a small amount of Ti0) exist on FTO. Electrochemical and photoelectrochemical measurements reveal that thin films of titanium species, expressed as TiOx, work as a compact blocking layer between FTO and TiO2 nanocrystaline film, improving Voc and the fill factor, finally giving a better conversion efficiency for dye-sensitized TiO2 solar cells with ionic liquid electrolytes.

Dye Solar Cells on ITO-PET Substrate with TiO[sub 2] Recombination Blocking Layers

“…Compared to the previous results in the literature [7][8][9]13], the data in Figure 4 demonstrates excellent recombination blocking characteristics: for the heat-treated FTOglass substrates the recombination currents here were one to two decades smaller, and for the substrates with blocking layer similar or lower than reported previously. …”

“…An optimal photoelectrode substrate forms a low resistance ohmic contact with the TiO 2 nanoparticle film, but effectively blocks electron transfer to the oxidized species (usually triiodide) in the electrolyte. This so-called recombination from the substrate has predominantly been studied in case of fluorine doped tin oxide (FTO) coated glass substrates [6][7][8][9][10][11][12][13]. Only recently other materials such as stainless steel have been examined [11].…”

“…Only recently other materials such as stainless steel have been examined [11]. In order to reduce the recombination losses, the use of blocking layers has been introduced [6,[8][9][10]13].…”

“…The effect of atomic layer deposited (ALD) TiO 2 blocking layers is studied as well. In literature the effect of blocking layers on open circuit voltage and fill factor varies considerably [6,[8][9][10]. Therefore a thorough and critical analysis is motivated to disaggregate the different ways these blocking layers contribute to the photovoltaic performance of the cell.…”

Electrochemical characterization of TiO2 blocking layers prepared by reactive DC magnetron sputtering

“…The majority of investigations deal, however, with TiO 2 blocking layers prepared by various methods. Spray pyrolysis is most commonly used, [4][5][6][7]11] but also sol-gel techniques, screen-printing [16], radio frequency magnetron sputtering of Ti followed by oxidation [17] and reactive sputtering of TiO 2 [18][19][20] have been applied.…”