Can 2-pyrone derivative act as an effective π-linker for dye-sensitized solar cells: a theoretical study?

Abstract

Thiophene and derivatives have been broadly used in metal-free organic dyes as π-bridge in the past 10 years. However, the relatively sharp and narrow visible absorption bands of these organic dyes not only severely attenuated the light capture capability but also restrict the efficiency. In this contribution, to design efficient sensitizers for dye-sensitized solar cells, a series of triphenylamine (TPA) dyes with 2-pyrone as the π-bridge are investigated using the density functional theory and time-dependent density functional theory approaches. The results show that the designed dyes have smaller gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, the absorption bands are greatly bathochromic-shifted by at least 39 nm and the light-harvesting efficiencies are improved compared to the experimentally efficient sensitizer T with thiophene as the π-bridge. The calculated values of free energy change ΔG inject for all the designed dyes are very negative, which favors electron injection from the excited-state dye to the TiO2 conduction band edge. Our simulations show that the sensitizers studied here are strongly adsorbed to the TiO2 cluster. During light excitation, electrons are transferred from the TPA group through the π-spacer to the surface-bound cyanoacrylate, facilitating electron injection to the TiO2 nanoclusters. Our calculations indicate that the newly designed dyes will be promising candidates for the future solar cell applications.