A Computational and Experimental Study of Thieno[3,4‐b]thiophene as a Proaromatic π‐Bridge in Dye‐Sensitized Solar Cells

Abstract

Four D-π-A dyes (D=donor, A=accpetor) based on a 3,4-thienothiophene π-bridge were synthesized for use in dye-sensitized solar cells (DSCs). The proaromatic building block 3,4-thienothiophene is incorporated to stabilize dye excited-state oxidation potentials. This lowering of the excited-state energy levels allows for deeper absorption into the NIR region with relatively low molecular weight dyes. The influence of proaromatic functionality is probed through a computational analysis of optimized bond lengths and nucleus independent chemical shifts (NICS) for both the ground- and excited- states. To avoid a necessary lowering of the TiO2 semiconductor conduction band (CB) to promote efficient dye-TiO2 electron injection, strong donor functionalities based on triaryl- and diarylamines are employed in the dye designs to raise both the ground- and excited-state oxidation potentials of the dyes. Solubility, aggregation, and TiO2 surface protection are addressed by examining an ethylhexyl alkyl chain in comparison to a simple ethyl chain on the 3,4-thienothiophene bridge. Power conversion efficiencies of up to 7.8 % are observed.

Metal-Free Sensitizers for Dye-Sensitized Solar Cells

“…Therefore, furan‐based sensitizers deserve more systematic studies with the view that furan and thiophene have similar chemical reactivity and studies of furan‐based dyes are rarer. The efficiency of DSSCs with the ETTC entity as the bridge has recently been improved to >7.41%96 after our publication. Further improvement of the cell performance is expected when the ester group at the thieno[3,4‐ b ]thiophene entity is removed to alleviate charge trapping.…”

Insights into the role of D‐A‐π‐A type pro‐aromatic organic dyes with thieno[3,4‐b]pyrazine as A acceptor group into dye‐sensitized solar‐cells. A TD‐DFT/periodic DFT study

“…Therefore, in recent years, the development of novel photosensitizers has been guided by chemical modifications to the acceptor group (A) . Prominent examples include, the PB1‐2, DP1‐2 dyes with thieno[3,4‐ b ]thiophene (TTh), and NL2‐NL8 sensitizers and FNE32‐FNE34 dyes with thieno[3,4‐ b ]pyrazine derivatives (TPy) as auxiliary electron acceptor groups (A). Both groups, TTh and TPy, have a quinoidal resonance structure, which is stable when the dye is in an excited state (see Figure ).…”

Theoretical Studies on the Structure, Optoelectronic and Photosensitizer Applications of NKX Class of Coumarin Dye Molecules

“…Density functional methods have emerged as promising and reliable tools for obtaining desirable results of dye sensitizers in DSSCs . These methods allow for the optimization of DSSC dyes in terms of either change in the structure or physical properties like, temperature, solvents, external field etc..…”