Theoretical study of 5,10-diphenylindeno[2,1-a]indene (DPI) dyes for dye sensitized solar cells (DSSC)

Abstract

Six D-DPI-A (D-π-A) dyes combining various arylamine electron donors (diphenylamine and triphenylamine moieties) with a fixed π-linker (DPI) and a fixed electron acceptor (cyanoacrylic acid) were designed to determine their electronic, photophysical and photovoltaic properties. It was found that electron-donating ability correlates positively with the energy of the highest occupied molecular orbital (E_HOMO) of the electron donor moiety. Optimized structures and electronic properties (highest occupied molecular orbital energy (E_HOMO), lowest unoccupied molecular orbital (E_LUMO), and energy difference (E_g) between HOMO and LUMO) were calculated by the density functional theory (DFT/B3LYP/6-31G(d)) method. Photovoltaic properties [electron injection driving force (ΔG_inj)] and photophysical properties [oscillator strengths (f), selected absorption wavelengths ($\lambda_{\text{abs}}^{\text{calc}}$) and light harvesting efficiency related to longest absorption wavelength (${\text{LHE}}_{{\lambda_{\text{longest}} }}$)] were calculated by the time-dependent density functional theory TD/BHandHLYP/6-31G(d) method. Both ΔG_inj and longest absorption wavelength (λ_longest) can be enhanced by increasing the electron-donating ability of the electron donor in these dyes. According to photophysical property analysis, λ_longest is the intra-molecular charge transfer band which can be regarded as the HOMO to LUMO transition. The electron density of HOMO is localized at the electron donor and the π-conjugated linker (DPI) moiety. The electron density of LUMO is trapped at the π-linker (DPI) and the electron-acceptor moiety. It is concluded that the electron-donating ability of the electron donor strongly influences the photophysical properties of the DSSC.