Table 1 presents a summary of the photovoltaic characteristics of the best-performing cell for each film thickness, along with the corresponding optimal dye adsorption time. The optimal dye adsorption time varies with the film thickness; thicker films require longer dye adsorption times. In addition, the attainable conversion efficiency depends on the photoanode thickness. A photoanode that is too thin or too thick results in a lower conversion efficiency. This is because insufficient film thickness leads to a low interfacial surface area, whereas an overly thick film aggravates unwanted charge recombination

and poses more restriction on mass transfer [14, 21, 30, 31]. Consequently, for the fabrication of ZnO/N719-based DSSCs, the dye adsorption time must be optimized simultaneously with the film thickness. A 26-μm-thick photoanode soaked in the dye solution for 2 h achieved the highest conversion efficiency (5.61%) www.selleckchem.com/products/azd-1208.html of all the cells prepared

in this study. Figure 4 shows the J V curve of the best-performing cell measured under 1 sun AM 1.5 G simulated light. Table 1 Optimal dye adsorption times and photovoltaic characteristics of best-performing cell at each film thickness Film thickness (μm) Optimal dye adsorption time (h) Conversion efficiency (%) Short-circuit photocurrent density (mA/cm2) Open circuit voltage (V) Fill factor 14 0.5 3.98 9.00 0.65 0.68 20 1 4.92 www.selleckchem.com/products/17-AAG(Geldanamycin).html 10.35 0.66 0.72 26 2 5.61 11.95 0.68 0.69 31 3 5.47 11.60 0.66 0.72 Figure 4 J-V curve of the best-performing cell. The cell was prepared with a 26-μm film sensitized in a dye solution for 2 h. To better

understand the effects of dye adsorption time on cell performance, this study also investigates dye loading in cells based on 26-μm-thick films. Figure 5 shows the correlation between J SC and dye loading as a function of dye adsorption time. The amount of adsorbed dye molecules increases continuously as the adsorption time increases, 17-DMAG (Alvespimycin) HCl whereas the J SC value reaches a maximum value and then decreases as the dye adsorption time increases. This observation is in contrast to that reported for TiO2-based DSSCs, where dye loading reached saturation after 2 h of sensitization and remained at the same level even when the sensitization time increased to 24 h [33]. The continuous increase of dye loading with sensitization time observed here suggests that the J SC deterioration is the result of dye aggregation. In this study, the ZnO film was sensitized with the weak acidic N719 dye, which was adsorbed onto the surface of ZnO particles through the carboxylic acid anchoring group. Compared to TiO2, ZnO is less stable in acidic dyes. Thus, immersing ZnO in an acidic dye solution for a long period can lead to ZnO dissolution and the formation of Zn2+/dye aggregates [32, 35–37].