Effect of 3,4‐ethylenedioxythiophene (EDOT) as Bridged Spacer on DSSC and Non Linear Optical (NLO) Properties: A DFT Approach.

Density functional theory (DFT) and time dependent DFT (TD‐DFT) techniques are used to explore six donor‐pi‐acceptor (D−A) type sensitizers that comprise coumarin as the donor unit and cyanoacrylic acid as the acceptor unit. It is examined how adding a spacer bridge like 3,4‐ethylenedioxythiophene (EDOT) affects the system. The introduction of EDOT leads to destabilization of highest occupied molecular orbital (HOMO) in both bare and TiO2 anchored sensitizers. The frontier molecular orbital (FMO) also depicts an effective intramolecular charge transfer from the EDOT unit to the acceptor unit in bare sensitizers and to the TiO2 core in TiO2 anchored sensitizers respectively. The FMO diagram of TiO2 anchored non‐bridged sensitizers reveals an electron‐deficient sensitizer unit coupled to an electron‐rich TiO2 core resulting in a poor charge transfer. The calculated Voc values are also found to be more for EDOT based sensitizers and hence making the EDOT bridged sensitizers efficient for DSSC application. According to the TD‐DFT investigation, the EDOT bridging sensitizers exhibit red‐shifted vertical excitation when compared to the corresponding non bridged sensitizers, which is consistent with the experimental data reported previously. [ABSTRACT FROM AUTHOR]