Analysis of Electron Transfer Properties of ZnO and TiO₂ Photoanodes for Dye-Sensitized Solar Cells

Abstract

Mesoporous TiO2 nanoparticle films are used as photoanodes for high-efficiency dye-sensitized solar cells (DSCs). In spite of excellent photovoltaic power conversion efficiencies (PCEs) displayed by titanium dioxide nanoparticle structures, the transport rate of electrons is known to be low due to low electron mobility. So the alternate oxides, including ZnO, that possesses high electron mobility are being investigated as potential candidates for photoanodes. However, the PCE with ZnO is still lower than with TiO2, and this is typically attributed to the low internal surface area. In this work, we attempt to make a one-to-one comparison of the photovoltaic performance and the electron transfer dynamics involved in DSCs, with ZnO and TiO2 as photoanodes. Previously such comparative investigations were hampered due to the morphological differences (internal surface area, pore diameter, porosity) that exist between zinc oxide and titanium dioxide films. We circumvent this issue by depositing different thicknesses of these oxides, by atomic layer deposition (ALD), on an arbitrary mesoporous insulating template and subsequently using them as photoanodes. Our results reveal that at an optimal thickness ZnO exhibits photovoltaic performances similar to TiO2, but the internal electron transfer properties differ. The higher photogenerated electron transport rate contributed to the performances of ZnO, but in the case of TiO2, it is the low recombination rate, higher dye loading, and fast electron injection.

ZnO Tetrapods: Synthesis and Applications in Solar Cells

“…The chemical stability of ZnO is, however, less than that of TiO 2 , which was found to be problematic in the dyeadsorption procedure. Low electron injection efficiency from excited dye molecules to ZnO is also an obstacle to obtaining high efficiency [66][67][68].…”

Impact of a Mesoporous Titania–Perovskite Interface on the Performance of Hybrid Organic–Inorganic Perovskite Solar Cells

“…Au) as the key components. The mp-TiO 2 layer in a typical dye-sensitized solar cell (DSSC) plays three major roles; provides a scaffold to increase the surface area of the absorber layer, act as a hole blocker, and transports photogenerated electron from the sensitized surface to the front contact 11 . Therefore, the active surface area which has a direct link with particle size of mesoporous material is a key parameter in DSSC 12 .…”

Photocatalytic Water Oxidation on ZnO: A Review

“…This observation has been attributed to the higher rate of recombination in ZnO compared to TiO 2 [17]. Two different radiative recombination processes were found to be involved in the excitonic emission of ZnO-free exciton recombination (slow) and near surface exciton recombination (fast) [19].…”

“…Despite possessing higher electron mobility, several studies have shown that ZnO demonstrated a lower photo-conversion efficiency compared to TiO 2 [17,18]. This observation has been attributed to the higher rate of recombination in ZnO compared to TiO 2 [17].…”