Significant Improvements of Near-IR Absorption, Electron Injection, and Oxidized Regeneration on Organic Sensitizers for Solar Cells

Physicochemical mechanisms of electronic absorption, charge injection, and oxidized regeneration in D-A-π-A organic sensitizers adsorbed on the TiO₂cluster were investigated. The D-A-π-A organic sensitizers contain the donors of triphenylamine derivatives, the π-linker bridge of thiophene, and the five kinds of heterocycle groups as additional acceptors (labeled -4, -N, -O, -S, -Si), as well as two acceptors (cyanoacrylic acid and a hydantoin moiety). Our results reveal the relationship between functional groups and physicochemical performance in the utility of D-A-π-A dye-sensitized solar cells. The results prove that the substitution of extra heterocycle acceptors possesses a small energy gap, resulting in a significant red shift expansion of the near-infrared absorption band compared with that of the original CA-4 and HY-4 dyes. Among the designed dyes, CA-O, CA-S, and HY-N possess a significant advantage in the intramolecular charge transfer (ICT) mechanism, the excited state lifetime, the electron injected time, the recombination rate, the adsorption, and the vertical dipole moment. Those parameters can direct them as potential candidates for realistic devices. The hydantoin anchor of HY-4 can inhibit the recombination process in which the injected electrons could escape from outer-path recombination, promoting oxidized dye regeneration and suppressing dye aggregation by weakening the intermolecular interaction efficiently. Besides, its molecular orbitals, transition properties, and interfacial electronic injection can be further improved by the external electric field ofF= 0.15 V/Å. Our results can also deepen the understanding of the physical principle of photogenerated charge transfer in the molecular system and provide valuable theoretical guidance for their molecular synthesis.