Theoretical investigation of organic dyes for dye-sensitized solar cell applications: effect of auxiliary acceptor groups

Abstract

Using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), the efficiency of a series of novel organic D-π-A-π-A dyes with different auxiliary acceptors in dye-sensitized solar cells (DSSCs) was predicted. The geometrical structures, electronic and optical properties and some key parameters related to energy conversion efficiency, such as light harvesting efficiency (LHE), electron injection driving force (ΔG_inject), electron regeneration energy (ΔG_reg) and excitation lifetime (τ) of all the investigated dyes were determined and discussed. In addition, dye/(TiO₂)₉ systems were also studied. The results show that all the dyes substituted by auxiliary acceptors (QL3–1 to QL3–5) have a very narrow energy gap, resulting in a broad UV–Vis absorption spectrum and a red shift in wavelength compared with the reference dye QL3. Among the dyes, QL3–4 and QL3–5 have a remarkably narrow energy gap, a significant red shift in peak wavelength (λ_max), a longer excited lifetime (τ) and a large dipole moment μ_normal that will produce a higher open circuit voltage (V_OC). This indicates that the organic dyes QL3–4 and QL3–5 are suitable dyes for improving the overall energy conversion performance of DSSCs.