First-Principles and Molecular Dynamics on A-D(II)-A Type Sensitizers for Dye-Sensitized Solar Cells: Effects of Various Anchoring Groups on Electronic Coupling and Dye Aggregation

The aggregation effect of five A-D(pi)-A organic dyes, 1-5, with different anchoring groups is investigated by a combination of first-principles and molecular dynamics (MD). The dye with CSSH anchoring group (2) exhibits improved optoelertronic properties with the wider absorption range and larger absorption strength as compared with the other four dyes. More importantly, the stacking dimer of 2 has smaller or equal electronic coupling as compared with 1, indicating more efficient electron injection from dye to TiO2. Besides the isolated dyes, the monomer and two H-aggregation configurations of 1 and 2 are adsorbed onto the TiO2 anatase (101) surface to evaluate the injection time and variation of the band gap. The aggregation would be suppressed by choice of the suitable anchoring groups. Even if the aggregation is formed, it is not totally detrimental for the photovoltaic efficiency. The influence of aggregation is complicated and should be evaluated from many aspects.