2.2.2. Fabrication of dye-sensitized solar cell (DSSC)

TEC7 FTO glass measuring 2 × 2 cm² was washed using soap and water, then the glasses were immersed in 70% ethanol and sonicated for 30 min. After that, the glasses were dried at 100 °C for 1 h, and the conductive side of the glasses was determined using a multimeter.

Photoelectrode was prepared by adopting the method of Rahmalia et al. [19]. The photoelectrode used was a mixture of TiO₂ anatase (2.3751 g), NH₄OH-activated metakaolinite (MKA) (0.1264 g), 15 mL of absolute ethanol, 16 drops of triton-x-100, and 12 drops of acetylacetone. The mixture was stirred for 24 h to form a paste, followed by sonication for 3 h.

Electrolyte was prepared by adopting the method of Rahmalia et al. [5] and Rahmalia et al. [15]. The 0.05 M I₂ was added to the KI solution (1.66 g in 20 mL of acetonitrile). The mixture was stirred until homogeneous. An amount of 5 mL of 1-methyl-3-prophylimidazolium iodide (MPII) 0.4 M ionic liquid was added to the mixture and was shaken carefully. The electrolyte solution was stored in a dark and closed bottle.

Two pieces of TCO glass with an active side of 1 × 1 cm² were prepared. Photoelectrode paste was dripped onto the surface of one glass using the doctor blade method. The glass was then heated in a furnace at a temperature of 450 °C for 30 min. Meanwhile, platinum paste was dripped into the other glass (as a counter electrode) and heated at a temperature of 400 °C for 5 min.

Photoelectrode was immersed in a sensitizer solution (36 g/L of Zn-astaxanthin in acetone) for 24 h. Furthermore, one drop of electrolyte was added and then covered with FTO glass which has been coated with a counter electrode to form a layer like a sandwich (Figure 1). As a comparison, DSSC with pure astaxanthin as a sensitizer was made using the same method. DSSCs using Zn-astaxanthin and astaxanthin were made in 3 cells each for repetition of the test in triplicate.

¹H-NMR (500 MHz) spectra of astaxanthin (a) and Zn-astaxanthin (b).

In the discussion section, photoelectrode immersed in Zn-astaxanthin and pure astaxanthin are called PE/Zn-astaxanthin and PE/astaxanthin respectively. In addition, the DSSC using Zn-astaxanthin and astaxanthin as sensitizers are called DSSC/Zn-astaxanthin and DSSC/astaxanthin, respectively.

The performance test was carried out by illuminating the DSSCs using a 500-watt halogen lamp with a light intensity of 0–1000 W/m². The light intensities were measured using a solar power meter. The short-circuit current (I_SC) and open-circuit voltage (V_OC) were measured using a multimeter 6.5 digits PICOTEST M3510. Furthermore, the stability of the cells was tested by illuminating the cells at maximum intensity for 10 h, determining the I_SC and V_OC values of the cells with an illumination period of 1 h. Cells were rested for 14 h in the dark and reilluminated continuously. Measurements were carried out for a total time of 70 h.