Electrochemical Characterization of TiO₂ Blocking Layers for Dye-Sensitized Solar Cells

Abstract

Thin compact layers of TiO2 are grown by thermal oxidation of Ti, by spray pyrolysis, by electrochemical deposition, and by atomic layer deposition. These layers are used in dye-sensitized solar cells to prevent recombination of electrons from the substrate (FTO or Ti) with the hole-conducting medium at this interface. The quality of blocking is evaluated electrochemically by methylviologen, ferro/ferricyanide, and spiro-OMeTAD as the model redox probes. Two types of pinholes in the blocking layers are classified, and their effective area is quantified. Frequency-independent Mott–Schottky plots are fitted from electrochemical impedance spectroscopy. Certain films of the thicknesses of several nanometers allow distinguishing the depletion layer formation both in the TiO2 film and in the FTO substrate underneath the titania film. The excellent blocking function of thermally oxidized Ti, electrodeposited film (60 nm), and atomic-layer-deposited films (>6 nm) is documented by the relative pinhole area of less than 1%. However, the blocking behavior of electrodeposited and atomic-layer-deposited films is strongly reduced upon calcination at 500 °C. The blocking function of spray-pyrolyzed films is less good but also less sensitive to calcination. The thermally oxidized Ti is well blocking and insensitive to calcination.

Optimization of a compact layer of TiO2via atomic-layer deposition for high-performance perovskite solar cells

“…Various conventional methods including spin coating, 18 spray pyrolysis, 19,20 electrochemical deposition 21 and thermal oxidation 22,23 were used to prepare a TiO 2 compact layer. With these methods, thermal post-treatments at high temperature (>450 C) are required to ensure adequate electronic contact.…”

Combined Experimental-Numerical Analysis of Transient Phenomena in a Photoelectrochemical Water Splitting Cell

“…22 Impedance spectroscopy measurements of the PEC cell, as shown in Figure S7, revealed a nonlinear capacitive behavior of the anodic interface, supporting the idea of charge carrier accumulation at interfaces. 29 We consequently introduced a model for surface states, which are expected due to the reactivity and high surface-to-volume-ratio of the porous electrode. 6 Previous experimental results from Rongéet al suggested that the photocurrent was controlled by two parallel adsorption processes.…”

Electrical field profile and doping in planar lead halide perovskite solar cells

“…Doping level of the TiO 2 compact layer can be measured by employing an electrochemical three-electrode setup in which FTO/TiO 2 forms the working electrode. 12 A suitable electrolyte plays the contacting role of the perovskite layer in solar cells. Capacitance measurements are shown in Fig.…”