A theoretical study of fused thiophene modified anthracene-based organic dyes for dye-sensitized solar cell applications
Anthracene-based conjugated materials have recently been developed as efficient sensitizers for applications in dye-sensitized solar cells (DSSCs). Anthracene DSSCs have been reported to show an impressive high power conversion efficiency of 12.6%. This paper reports a density functional theory study on a series of metal-free fused thiophene modified anthracene dyes. The effects of fused thiophene units on the spectra and electrochemical properties of the anthracene dyes are computationally demonstrated. Our calculations show that with the sizes of the oligothienoacene units increasing from thienothiophene, dithienothiophene, to tetrathienoacene, the lowest-energy absorption peaks basically remain the same, however the oscillator strength gradually increases and the adsorption bands systematically broaden. When cyclopentadithiophene with a similar size to dithienothiophene is incorporated into the donor part, a remarkable 43 nm red-shift of the absorption peak and a broader absorption band are found, with a similar oscillator strength. The calculated ultra-fast injection time of electrons from the excited state of all anthracene dyes to the conduction band of TiO2 is ideal for DSSC applications. The newly designed anthracene dyes in this article show desirable energetic, electronic, and spectroscopic parameters for future DSSC applications.