Effect of Surface Etching on the Efficiency of ZnO-Based Dye-Sensitized Solar Cells

Abstract

In this study, we report on an insight into the influential factors of the conversion efficiency of ZnO-based dye-sensitized solar cells. With ZnO nanoflowers as the photoelectric anode and dye N719 as the sensitizer, we found with the addition of N719 that the surfaces of ZnO nanoflowers were slightly etched at the beginning and gradually destroyed with time. On the basis of these observations, a series of experiments were further carried out to distinguish the influence of dye-induced aggregation from that of dye-induced etching on the solar-to-electric conversion efficiency. SEM observation reveals that there were no obvious dye/Zn(2+) aggregations on any of the samples. XRD results indicate that there was no new phase formed during the dye-sensitizing process. I-V measurements reveal clearly that the efficiency of ZnO-based DSSCs was inversely proportional to the etching level of ZnO surfaces. We concluded that the dye-induced etching of the ZnO anode may be an assignable cause that results in the low efficiency of ZnO-based DSSCs. The etching of ZnO may lead to low surface absorption efficiency of the dye, low electron mobility, and a high surface recombination ratio of photocarriers. Therefore, we suggest that special attention should be paid to protecting the surface structure of the ZnO anode during the dye-sensitizing process.

Optimization of dye adsorption time and film thickness for efficient ZnO dye-sensitized solar cells with high at-rest stability

“…Dye aggregation leads to slower electron injection and higher charge recombination [36,37]. The end result is a lower J SC and overall conversion efficiency [39]. These reports support the trends of τ eff and J SC versus dye adsorption time observed in this study.…”

“…For example, when a dye adsorption time of 3 h (optimal for the 31-μm film) was applied to the 20-μm film, the conversion efficiency dropped from the peak value of 4.95% to approximately 3.4%, representing a 31% drop. Prolonged dye adsorption times cause dye aggregation [32,35-38] and etching of the ZnO surface [39], both of which result in performance deterioration in ZnO-based DSSCs. Conversely, TiO 2 -based DSSCs are typically less sensitive to prolonged sensitization times because of the higher chemical stability of TiO 2 [32-34].…”

“…When dye molecules undergo aggregation, electron injection becomes less efficient, and overall conversion efficiency declines. However, Yan et al [39], on the other hand, observe the surface etching of ZnO nanoflowers after a long sensitization time. Surface etching also leads to a significant loss in overall conversion efficiency.…”

Organic and inorganic surface passivations of TiO2 nanotube arrays for dye-sensitized photoelectrodes

“…It was reported that ZnO is etched by N719 dye molecules resulting in deterioration of DSCs [25]. Although Diamant et al said that basic coating layers shift conduction band in negative direction [26], a direct proof that present conduction band shift by coating layers was not shown in this study.…”

High performance of Mn-doped CdSe quantum dot sensitized solar cells based on the vertical ZnO nanorod arrays

“…Significantly, the high-electron mobility (~130e200 cm 2 V À1 s À1 ) and direct conduction path of vertical ZnO arrays would benefit electron transport with less recombination and enable the possibility for a larger open circuit voltage (V oc ) [23,26]. Further, ZnO has similar band gap (~3.2 eV) in comparison with TiO 2 [27]. Hence, vertical aligned ZnO arrays has been explored as electrodes in sensitized solar cells with great potential.…”