Evaluation of Novel Glycerol/PEO Gel Polymer Electrolytes for Non-Toxic Dye-Sensitized Solar Cells with Natural Dyes Regarding Long-Term Stability and Reproducibility

Abstract

Alongside efficiency, long-term stability of dye-sensitized solar cells (DSSCs) is a key factor regarding their commercialization. One suitable and cost-effective method to increase the long-term stability is to prevent leakage and evaporation of the electrolyte by gelling it with polymers such as poly(ethylene oxide) (PEO) and gaining a gel polymer electrolyte (GPE). In this study, a GPE based on PEO and glycerol is investigated for the first time as electrolyte for environmentally friendly DSSCs with natural dyes. To evaluate the novel glycerol/PEO GPE, the ionic conductivity and resulting efficiency progressions of DSSCs were measured for 75 days. Different molecular weights (MWs) of PEO and blending with poly(vinylidene fluoride) (PVDF) had negligible impact on efficiencies. 17 wt% PEO was found to be more suitable than lower concentrations and resulted in a relatively high efficiency over 75 days. A glycerol electrolyte without PEO had higher ionic conductivity and achieved higher efficiencies as well but leaked from the unsealed DSSCs. In addition, the reproducibility was examined especially, which appeared to be reduced by considerable differences between identical DSSCs and between measurements of the same DSSC at different times. This emphasizes the relevance of studying multiple DSSC per sample to ensure reliable results.

Investigation of the Long-Term Stability of Different Polymers and Their Blends with PEO to Produce Gel Polymer Electrolytes for Non-Toxic Dye-Sensitized Solar Cells

“…Table 2 shows the results of the ionic conductivity measurements for the different GPEs used to build the DSSCs. The value of the reference electrolyte was taken from Reference [27], where it was measured under identical conditions. For each sample, the three assembled DSSCs were studied for 21 days to examine the most efficient DSSC per sample and their reproducibilities.…”

“…Isolated downward deviations in efficiency, e.g., reference DSSC c on day 19 (Figure 1a) or sample 3a on days 5, 12 and 14 (Figure 1b), are probably due to deviations in measurement, which is probably caused by damaged conductive layers on the electrodes due to the attachment of measuring clamps [27]. The general differences in efficiency indicate deviations in the manufacturing process or in the raw materials of the DSSCs per sample [27]. These can for instance be caused by the pressure, by which the glass electrodes are pressed together, or by the manually applied graphite coatings on the counter electrodes [6,26,27,30].…”

“…The general differences in efficiency indicate deviations in the manufacturing process or in the raw materials of the DSSCs per sample [27]. These can for instance be caused by the pressure, by which the glass electrodes are pressed together, or by the manually applied graphite coatings on the counter electrodes [6,26,27,30]. Even though the best DSSCs were considered for the assessment of long-term stability, the general validity of the results is limited by the low reproducibility.…”

“…An exact comparison of the DSSCs is difficult due to the different additives in the electrolyte and differences in the general structure of the DSSC. Additionally, the problematic reproducibility makes accurate comparisons between DSSCs developed by different researchers difficult [27]. Furthermore, the approach chosen here was to optimize long-term stability and not efficiency.…”

“…In comparison to earlier publications, more reproducible but also thicker glass plates are now used for the DSSCs, so that higher losses could occur here before the light hits the anthocyanins. Furthermore, the comparatively lower efficiencies are due in particular to observed deviations in the forest fruit tea as the basis for the natural dye, the use of a black background in the measurement and the generally problematic reproducibility [27]. Finally, the comment by Ehrmann and Blachowicz [51] should be mentioned, which notes out that some of the efficiencies of DSSCs with natural dyes found in the literature have unfortunately been calculated too high (mostly by a factor of between 10 and 100) and, thus, place too high an expectation on the efficiencies of non-toxic DSSCs with natural dyes.…”