Effects of structural optimization on the performance of dye-sensitized solar cells: spirobifluorene as a promising building block to enhance Voc

We prepared three new push-pull dyes JA3, JA4 and JA0 through structure optimization, and applied them in DSSCs. Judicious molecular structure optimization of dyes can significantly improve the performance of DSSCs. Spirobifluorene as a building block was introduced onto the phenothiazine donor groups. Compared to JA1, the steric effect of the spirobifluorene building block can effectively reduce charge recombination by preventing the I-3(-) of the electrolyte penetrating into the TiO2 surface, thus the V-oc of JA3 increased from 701 mV to 800 mV. In order to further improve the light-harvesting ability of the DSSC, we introduced a benzothiadiazole unit (BTD) and prepared D-A-pi-A dye JA4. As expected, the J(sc) of JA4 increased from 12.32 to 14.43 mA cm(-2) compared to that of JA3, and the device reached the highest PCE of 7.0%. Moreover, since extending the pi-conjugated system is known to decrease the V-oc of DSSC, the porphyrin unit was removed and dye JA0 was synthesized. Notably, the DSSC based on JA0 reached a very high V-oc of 840 mV and a high PCE of 6.69%: to our knowledge, this is the highest V-oc for DSSCs based on phenothiazine dyes with I-/I-3(-) electrolyte.