## 2 Materials and Methods  
Glass electrodes coated with fluorine-doped tin oxide, whereby the front electrodes were additionally pre-coated with a TiO\({}_{2}\) layer, and the liquid electrolyte for the reference sample, were purchased from Man Solar (Petten, The Netherlands). The exact formulation of the reference electrolyte is unfortunately not known. To gain a catalyst layer on the counter electrodes, graphite was applied using a graphite pencil with a hardness of 6B (Faber-Castell, Stein, Germany), which is a common technique [26]. The semiconductor layers on the front electrodes were dyed by inserting them in a solution containing natural anthocyanins for 10 min. This solution was previously extracted from 10 g forest fruit tea (Mayfair, Wilken Tee GmbH, Fulda, Germany), which proved to be a suitable and low-cost source of the natural dyes [5], in 120 mL distilled water by stirring for 15 min at room temperature with a filtering step thereafter. After dyeing of the TiO\({}_{2}\) layer, the front electrodes were rinsed with distilled water and dried at room temperature. To gain a polymer blend, 600,000 g/mol PEO from S3 Chemicals (Bad Oeynhausen, Germany) was mixed with PAN as L-PAN, kindly provided by Dralon GmbH (Dormagen, Germany), ABS (3D printing filament, Filamentworld, Neu-Ulm, Germany), PVA under the brand name GOHSENOLTM (NIPON GOHSEI Europe GmbH, Dusseldorf, Germany), and PVDF with Amboflon(r) as the brand name (Ambofluor GmbH Co. KG, Hamburg, Germany). For comparison, these polymers were also utilized without PEO as the basis for GPEs. The composition of each sample is depicted in Table 1.  
Concerning the here-presented GPEs, the iodide-trtiodide redox couple was based on potassium iodide (KI) purchased from VWR (Darmstadt, Germany) mixed at a weight ratio of 2:1 with molecular iodine (I\({}_{2}\)) purchased from [PERSON] (Karlsruhe, Germany), inspired by [PERSON]'s solution. These electrolytic salts were dissolved in DMSO ([PERSON], Karlsruhe, Germany). For each sample depicted in Table 1, the related polymers were subsequently added. The components of the GPEs were stirred at 70 \({}^{\circ}\)C for at least 1 h and occasionally more DMSO had to be added to achieve a similar and well applicable consistency. After dissolving, the GPE of each sample was coated on the graphite layered counter electrodes using a doctor blade with a wet layer thickness of 30 \(\upmu\)m. Three unsealed DSSCs were assembled per sample by placing the front electrodes on the GPE layer and attaching them with transparent tape. The DSSCs were deliberately not sealed, as the long-term stability of the electrolyte was also to be investigated in terms of possible evaporation. The measurements of the GPEs with respect to their ionic conductivities were carried out at a temperature of 40 \({}^{\circ}\)C with a LWT-01 Voltcraft conductivity pen (Conrad Electronic, Wollerau, Switzerland). To evaluate the potential benefit of the GPEs regarding their long-term efficiency, measurements of the I-U curves were conducted using a Keithley 2450 source meter (Tektronix Inc., Beaverton, OR, USA) over a maximum of 120 days. They were measured at room temperature under illumination with an AM 1.5 G spectrum and 100 mW/cm\({}^{2}\) from a LS0500 solar simulator (LOT-Quantum Design GmbH, Darmstadt, Germany) with a black background to prevent light reflected behind the DSSC from re-entering it. After the measurements, the efficiencies were calculated and the results of all DSSCs per sample are shown for the first three weeks and the best DSSC for each sample is shown over 120 days.