Roles of Chenodeoxycholic Acid Coadsorbent in Anthracene-Based Dye-Sensitized Solar Cells: A Density Functional Theory Study

In the present work, the coadsorption of the 4-(7-{10-[bis­(4-hydroxy-phenyl)-amino]-anthracen-9-ylethynyl}-2-octyl-2H-benzotriazol-4-yl)-benzoic acid (TY6) dye and the chenodeoxycholic acid (CDCA) coadsorbent on the anatase TiO2(001) surface as crucial components of a high-performance dye-sensitized solar cell (DSSC) has been investigated using density functional theory. Our results show that the CDCA coadsorbent plays an active role not only in stabilizing the dye/oxide system but also in preventing the surface tensile stress induced by the dye monolayer. The monolayer of the TY6 dye at high surface coverage in the absence of the coadsorbent applies tensile stress to the TiO2(001) surface because of the repulsive interactions between polar TY6 molecules. The induced tensile stress will shift both the valence band and the conduction band to higher energy, which reduces the energy gap between the lowest unoccupied molecular orbital (LUMO) of TY6 and the conduction band maximum (CBM) of TiO2(001). The reduced LUMO–CBM gap is detrimental to the charge injection efficiency of the DSSC, which results in a loss of power conversion efficiency. The coadsorbent increases the spacing between the dyes to reduce the surface tensile stress and thus prevents the decrease in the charge injection efficiency