Significant enhancement in efficiency of NKX-2807 Coumarin dye by applying external electric field in dye sensitizer solar cell: Theoretical study

We present calculations of various properties of the ground and excited electronic states of Coumarin NKX-2807. An extensive Density Functional Theory (DFT) and Time Dependent DFT study of this sensitizer was performed, investigating on the electronic structure and optical properties of the dye both in the gas phase and in ethanol solution. The absorption bands are assigned to π → π∗ transitions. We also examine the ground and excited-state dipole moments and polarizability of this Coumarin dye. Solvents (ethanol) are found to induce a red shift of the vertical excitation energies, and their effects on the molecular geometry and the electronic structure are studied in detail. Electric fields influence any process or transition that involves charge transfer, effect of a strong external electric field on the absorption spectrum is evaluated. The effect of the electric field is observed as a broadening of the absorption band if there is a change in the dipole moment and polarizability upon excitation. The results of this work show that field application, parallel to the dipole moment, can be very effective to increase DSSC efficiency. Our results open the possibility of computationally screening the various predictions on the electronic structure, optical response and in consequence their influences on the efficiency, thus paving the way to an effective molecular engineering of further enhanced sensitizers for solar cell applications.