Influence of vibronic contribution on light harvesting efficiency of NKX-2587 derivatives with oligothiophene as π-conjugated linker

Abstract Based on the NKX-2587 molecule we designed ten sensitizers with 1–10 thiophene moieties to investigate how the number of thiophene unit in the spacer influences the absorption spectra of sensitizer in dye sensitized solar cells (DSSCs). The parameters of short-circuit current density ( J sc ), open circuit voltage ( V oc ), the light harvesting efficiency ( LHE ), injection driving force ( ∆ G inject ), and transferred electron number ( n c ), were calculated and discussed in detail. Results indicated that the increasing of thiophene units makes for the enhancement of oscillator strengths ( f ), although the red shift of vertical electronic absorption spectra is small. For the designed sensitizers with 1–5 thiophene units, their Δ G inject and n c raise gradually with the increasing of thiophene number. However, for those sensitizers with 6–10 thiophene units, the Δ G inject and n c decrease continuously with the increasing of thiophene units. In order to study how the oligothiophene as π-conjugated linker affects light harvesting efficiency of DSSCs, the vibrationally resolved electronic spectra of five metal-free NKX-2587 derivatives with 1–5 thiophene units were simulated within the Franck-Condon approximation including the Herzberg-Teller and Duschinsky effects. The present theoretical results provided helpful guidance for understanding the sources of spectral intensities of dye molecules, and a valuable method for rational design of new molecules to improve the energy conversion efficiency ( η ) of DSSCs.