Insights into the role of D‐A‐π‐A type pro‐aromatic organic dyes with thieno[3,4‐b]pyrazine as A acceptor group into dye‐sensitized solar‐cells. A TD‐DFT/periodic DFT study

Time‐dependent density functional theory (TD‐DFT)/periodic DFT calculations were performed to determine the role of pro‐aromatic organic D‐A‐π‐A type dyes (the NL1‐NL17 family) with Thieno[3,4‐b]pyrazine (Tpy) as A acceptor group into dye‐sensitized solar‐cells (DSSC). This work presents a discussion of the ground and excited states of these dyes along with the aromaticity analysis and the electron injection step using a dye@(TiO2)72 model. The results suggest that the pro‐aromatic behavior increases from the thiophene ring to the pyrazine when an acceptor π‐bridge such as phenyl is used. This strong pro‐aromaticity is also reflected in the electron injection step, studied using a 3x2 3 layer (TiO2)72 slab model. The resulting adsorption energies (ΔEads and ΔGads) and the electron injection (ΔGinject) in the stablest coordination mode, Bid_CN_COOH, indicate that the redox reaction (Dye* ➔ Dye+ + e−) is stronger and more spon than the adsorption reaction (Dye+ + TiO2 [+e−] ➔ Dye@TiO2) in the electron injection. In this way, the highest efficiency of NL6 and NL12 is a consequence of the more significant pro‐aromatic characteristics and the more spontaneous redox process. Finally, these NL dyes are promising in the molecular engineering of D‐A‐π‐A metal‐free types dyes. NL dyes (D‐A‐π‐A) with Thieno[3,4‐b]pyrazine as A acceptor group for DSSC are studied using a dye@(TiO2)72 model. NL6 and NL12 are the most efficient dyes as consequence of the greater pro‐aromatic features.