## 4 Discussion  
Investigating and presenting the reproducibility of the assembled DSSCs with Figure 1 is necessary to face the known problem of low reproducibility of DSSCs in the greater context of the reproducibility crisis of science [6; 28; 30; 31; 32; 33; 34]. From the observed deviations in the efficiency curves of identical DSSCs per sample over 21 days, it is evident that the DSSCs investigated here have poor reproducibility. 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),  
Figure 7: I-U curves of PAN blended with PEO (sample 1), ABS blended with PEO (sample 4), PVA blended with PEO (sample 6), PVDF blended with PEO (sample 8) GPEs and a reference for: (**a**) day 0; (**b**) day 28; (**c**) day 59; and (**d**) day 110.  
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]. 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 improvement of the reproducibility is essential for future research. As is apparent in Figures 2-5, the GPE blends based on PEO show a clearly higher long-term stability and efficiency than the GPEs with only one polymer. In Figures 6 and 7, the measurements of these GPEs mixed with PEO, namely PAN/PEO (sample 1), ABS/PEO (sample 4), PVA/PEO (sample 6) and PVDF/PEO (sample 8), are compared with a reference DSSC. The reference DSSC, which steadily deteriorates (decreasing efficiency) during the measurement, shows a higher energy conversion efficiency than the GPE DSSCs during the first week. The maximum efficiencies of the DSSCs achieved after several days can be explained by the comparatively slower penetration of the nanoporous TiO\({}_{2}\)/dye layer by the GPE [10; 26; 28; 30]. This pore filling and the resulting contact depends on the structure of the respective polymer [9; 35]. Samples 1 and 8 had the least degradation after their peak efficiency, which can also be seen from their relatively constant I-U curves. According to current literature, the effectiveness of unsealed DSSCs with liquid electrolyte decreases due to leaking and drying of the electrolyte over time [6; 7; 36]. Thus, because the reference DSSC was not rehydrated during the long-term measurement, a steady reduction in efficiency to a point of malfunction was expected and observed [37]. The positive effect of PEO was already described by [PERSON] et al. [38] before, therefore a good long-term stability of the PEO blended GPEs were also expected and observed. Thanks to the gelling effect of PEO, a stable framework is created, which decreases leakage and evaporation of the GPE [7; 11; 38; 39]. However, GPEs also have some disadvantages, as the contact of the GPEs with the dye and TiO\({}_{2}\) layer is worse compared to a liquid electrolyte and increased crystallinity of PEO further reduces the energy conversion efficiency [7; 9; 11; 35; 40]. Therefore, it is suggested to blend the polymers PAN, ABS, PVA and PVDF with PEO to adjust the viscosity and reduce the crystallinity of the GPE, which leads to a better penetration of the TiO\({}_{2}\) semiconductor, ionic conductivity and overall better energy conversion rate [38; 41]. Here, the PAN/PEO blend (sample 1) reaches the highest efficiencies of all GPE DSSCs and shows the best long-term stability. As already mentioned, the types of conductivity of the two polymers are different, but their properties seem to be complementary.