Theoretical study of the effect of π-linkers on triarylamine-based p-type D-π-A sensitiser

Abstract

ABSTRACTSix p-type dyes with D-π-A structures were designed, and their molecular structures and electronic properties were studied by the density functional theory and the time-dependent density functional theory. Thiophene, thiophene[3,4-c][1,2,5] thiadiazide and thiazole[5,4-d]thiazole in combination with dithieno[3,2-b:2',3'-d]thiophene (s-DTT) were introduced into the newly designed dyes to extend π-linkers. The results showed that the enhanced conjugation of π-linkers increases the coplanarity and decreases HOMO–LUMO gap of the dyes. The absorption spectra of dyes 1–6 are obviously red-shifted. Compared to those of QT-1, the spectra of dyes 3 and 6 are red-shifted by 128 and 154 nm, and the oscillator strengths are improved by 70% and 71%, respectively. Dyes 3 and 6 have not only the strongest absorption peaks, but also a large absorption area in the range of 400–900 nm. This guarantees them stronger light absorptions. They also have the maximum charge separation degree (t), resulting a reduced hole recombination. Furthermore, the light harvesting efficiency (LHE), hole injection power (ΔGinj), dye renewable power (ΔGreg) and charge recombination force (ΔGCR) of dyes 3 and 6 are superior to those of other dyes. In addition, the bromine substitution can effectively promote the red-shift of the absorption spectra.