Theoretical Study of the Effect of the Terminal Groups of Triphenylamine Donors on the Photophysical Properties of D-A-π-A Dye Sensitizers.

In this paper, a set of D-A-π-A type sensitizers with a triphenylamine core as an electron donor were investigated by using the DFT/TD-DFT method. With the aim of finding the most suitable substitution by adding extra donor groups to triphenylamine. The donor fragments are acetyl (TPA-1), benzene with acetyl (TPA-2), triphenylamine (TPA-3), and triphenylamine with acetyl (TPA-4). Extension of the donor groups in TPA-1 to TPA-3 dyes results in a progressive reduction of the energy gap (2.31 eV< 2.16 eV< 1.83 eV), accompanied by a red-shift in their UV-Vis absorption maxima (491.71 nm< 510.54 nm< 524.47 nm). It is mainly attributed to the fact that the addition of acetyl groups destroys the original donor conjugate structure, which reduces the degree of π-electron delocalization of the system. In other words, the mindless expansion of the donor structure is not a reasonable way to improve the performance of DSSCs. In addition, TPA-3 shows excellent advantages in excited state properties, photovoltaic parameters, and global chemical reactivity descriptors, which makes it one of the most beneficial sensitizers in the prospect of this paper.