TiO
2-DWCNT content affects dye adsorption amount on the flexible TiO
2 film. Figure 5 shows the absorption spectra of dye N719 desorbed from the flexible TiO
2 films with the same thickness and with different TiO
2-DWCNTs percentages. According to the Lambert-Beer’s law, higher absorbance means the more dye N719 absorbed on the TiO
2 film, which is in favor of enhancing the photocurrent of the flexible DSSC [
15]. It is obvious that the absorbance for the sample with 0.50 wt.% TiO
2-DWCNTs is the highest, the samples with 0.25 wt.% and 0 wt.% TiO
2-DWCNTs are lower, and the sample with 0.75 wt.% TiO
2-DWCNTs is the smallest. As reported in Refs. [
16,
17], incorporating CNTs in a TiO
2 matrix will decrease the TiO
2 crystallinity or the reduce TiO
2-CNTs size due to the interaction between CNTs and TiO
2. Moreover, smaller particles or crystallinity result in larger surface area of the materials, which will provide more surface active sites for adsorbing dye molecules. Besides, the roughness factor of the TiO
2 film was enhanced by adding DWCNTs, which increase dye adsorption. However, higher loaded TiO
2-DWCNTs (0.50 wt.%) may cause the formation of DWCNT aggregation and decrease the adsorption of TiO
2 film to the dye. In our experimental conditions, the TiO
2 film contained 0.50 wt.% TiO
2-DWCNTs can absorb most dye N719 [
16-
18].