The effect of electrolyte filling method on the performance of dye-sensitized solar cells

Abstract

The effect of electrolyte filling method on the performance of the dye-sensitized solar cells is investigated with the segmented cell method, a recent technique which is very simple but effective as it can be used to examine all the photovoltaic characteristics. The electrolyte filling techniques compared were single injection, which is typically used in small laboratory cells, and pumping the electrolyte through the cell several times, which is often used for larger cells and modules. Significant photovoltage and photocurrent variations occur with the repeated pumping of the electrolyte in the cell preparation.Transient and charge extraction measurements confirmed that the differences in open circuit voltage were due to the shifts of the TiO2 conduction band and time correlated single photon counting confirmed that the reduction of short circuit current was largely due to reduced electron injection correlated with the increasing conduction band edge in the studied cases. This was interpreted as an effect of molecular filtering by the TiO2 causing an accumulation of electrolyte additives (4-tert-butylpyridine and benzimidazole) near the electrolyte filling hole, the concentration of which increased with repeated pumping of the electrolyte. Interestingly, spatial variations were seen not only in the relative TiO2 conduction band energy but also in the density of trap states. In this contribution it is demonstrated how the changes in the conduction band can be separated from the changes in the density of trap states which is an essential for the correct interpretation of the data.

Nanocellulose aerogel membranes for optimal electrolyte filling in dye solar cells

“…Here we applied a commercial electrolyte so unfortunately the used voltage increasing agent is unknown to us. Based on previous studies, it is known that the effects of different voltage increasing agents are quite similar [3][4][5] and the commercial electrolyte used here is known to have similar spatial performance issues as the ones with known compositions [4]. It is seems very likely that here the reference cells have a higher voltage as significantly larger amount of the voltage increasing agent has been adsorbed in the dyed TiO2 film in the electrolyte filling.…”

“…In contrast, the way how the electrolyte comes in touch with the photoelectrode has been shown to have the observed effect on the performance characteristics [3][4][5][6]. In the reference cells, the electrolyte is pushed laterally through the dyed TiO2 film (length 8 mm).…”

“…Also, the porous dyed TiO2 layer acts as a filter adsorbing some of the electrolyte additives leading to an uneven distribution of the electrolyte components in the cell. Hence, significant spatial variations in the performance may result [3][4][5][6]. The efficiency losses due to this spatial effect have been as high as 35% [4].…”

“…The effects can be reduced to some extent by changing e.g. the electrolyte composition [4][5][6]. Optimally, the electrolyte filling method should intrinsically result in an even spatial distribution.…”

Interpretation of Optoelectronic Transient and Charge Extraction Measurements in Dye‐Sensitized Solar Cells

“…Although it is increasingly common to compare electron lifetimes as a function of charge, there is emerging evidence showing that some electrolyte additives can not only change the concentration of charge for a given voltage, but also the concentration of charge for a given current 64, 97. If the diffusion coefficient of free electrons has not changed, this implies that these additives or dyes may modify the distribution (or concentration) of trapping states in addition shifting the semiconductor conduction band 98, 99.…”