Second order hyperpolarizability of triphenylamine based organic sensitizers: a first principle theoretical study

Designed metal-free dyes have been investigated by Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) to evaluate the ground state and excited state geometries of triphenylamine-based organic sensitizers. The optoelectronic properties of five types triphenylamine (TPA)-based dyes, namely, C206, TPA, TPA-N(CH3)(2), TPA-SCH3, and TPA-OC2H5, were studied. Energy band modulation has been performed for these dyes with different electron donating groups and the same electron withdrawing group. The performance of the hybrid functionals B3LYP and wB97XD using a standard basis set, 6-311++ G(d,p), has been analyzed. Solvent effects have been examined by Conductor-like Polarizable Continuum Model (C-PCM) formalisms. The C-PCM/TD-DFT results show that accurate absorption energies are obtained only when the solvent effect is included in the excited state geometries. Theoretical examination of the non-linear optical (NLO) properties was performed on the key parameters of static polarizability and first order and second order hyperpolarizability. Good photovoltaic performance based on the optimized geometry, the relative position of the frontier molecular orbital energy levels and the absorption maxima of the dye are expected for offering a remarkable response. The results provide a direction for optimizing dyes as efficient sensitizers in dye-sensitized solar cells (DSSCs) and NLO applications.