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 (EHOMO) of the electron donor moiety. Optimized structures and electronic properties (highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital (ELUMO), and energy difference (Eg) between HOMO and LUMO) were calculated by the density functional theory (DFT/B3LYP/6-31G(d)) method. Photovoltaic properties [electron injection driving force (ΔGinj)] 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 ΔGinj and longest absorption wavelength (λlongest) can be enhanced by increasing the electron-donating ability of the electron donor in these dyes. According to photophysical property analysis, λlongest 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.