Growth and Photovoltaic Performance of Single-Crystal TiO₂ Nanorod Array Directly on Transparent Conducting Substrates

Abstract

In this study, single-crystal TiO2nanorod (NR) arrays were used as the photoanodes of dye sensitized solar cells (DSSC). The post-annealing treatment was carried out in air, O2, N2and vacuum atomsphere. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) have been used to characterize the structure, morphology and crystallity of these samples. Although the nanorod arrays which undergo annealing remained the single-crystal structure without any change in the morphology, considerable improvement in the nanorod solar cell performance was obtained. The high efficicency of 4.42 % was achieved in the cells containing nanorods which were annealed in air at 500 °C for 30 min. In comparison, the cell fabricated using TiO2samples without post- annealing treatment exhibited a low efficiency of just 2.1 %. Such a large improvement (280 %) was mainly attributed to the faster electron transport and the lower charge recombination rate after annealing due to an increase of the depletion width. Otherwise, the cell performance improvement may result from an enhancement in the adhension and electrical contact at the TiO2/FTO interface. The in-depth study shows that the solar cell efficiency was strongly dependent on the annealing ambience, too.

Influence of annealing temperature on performance of dye-sensitized TiO2 nanorod solar cells

“…Such a behavior has been demonstrated by a comparison of UV-visible absorption spectra indicated in our previous report [22]. In that report, the dye-sensitized TiO 2 NR array which underwent annealing exhibited a higher absorption coefficient over the visible band than that which didn't undergo annealing.…”

“…As is well known, V OC is related mainly to the electron concentration in the conduction band of TiO 2 [29]. Hence, the increase of V OC over the range of RT-600°C can be mainly ascribed to the increased electron injection or the reduced recombination of electrons [22].…”