Rational tailoring of C275 towards promising organic dyes: Enhancing light absorption and charge separation

Abstract Designed with electron-donating and electron-withdrawing moieties as donors and acceptors, respectively, a series of novel organic dyes for dye-sensitized solar cells (DSCs) are simulated using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods The interacting dye/TiO 2 systems are also studied to further explore the interfacial injection process of photo-excited electron. The model dye C275 is featured with donor/acceptor (D/A) molecular architecture, which is primary to achieve the easy charge-transfer excitation and suitable energy levels alignment. To date, considerable efforts are devoted to the design and synthesis of D/A type organic dyes, and the initial configurations are typically comprised of N-annulated perylene donor, porphyrin linker, and carboxylic acid acceptor. Our results show that, the electronic levels and optical absorption properties can be tuned gradually by introducing auxiliary donor units or electron-deficient spacer in acceptor groups. Moreover, the designed dyes also exhibit good performance in terms of photoinduced charge transfer, electron injection, and dye regeneration, etc . Through structural modification of donor moieties, the new tailored dyes provide appropriate energy levels, strong light-harvesting and easy charge separation. Meanwhile, the distinct red-shift of optical absorption and large amount of transferred charges are also obtained by structural tailoring of acceptor groups, whereas the large values of injection time may be harmful for the interfacial photoelectron injection. Therefore, comparing with donor modification, it should be more carefully to choose appropriate acceptor group with the balance of various energetic and kinetic factors for the rational design of high-efficient organic dyes.