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

Abstract

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 I₃⁻ 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–π–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 π-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⁻/I₃⁻ electrolyte.