The function of Chalcogenophene in the Cyclomatelated Ring of the Cycloruthenated Dyes applied in Dye-Sensitized Solar Cell

Abstract

Three thiocyanate-free cycloruthenated complexes, DUY24-O, DUY24, and DUY24-Se containing furan, thiophene, and selenophene, respectively, as a part of the cycloruthenated ring, were designed to reveal the function of the chalcogen atom on the physicochemical and photovoltaic performance of the cycloruthenated sensitizers applied in dye-sensitized solar cells (DSCs). The three sensitizers have a similar molecular size; therefore, the effect of molecular dimensions on their photovoltaic performance can be negligible. NMR data, electron-donating resonance effects, optical properties, and the energy levels of the frontier orbitals reveal that the physical/ photovoltaic properties of the three sensitizers were affected significantly by the chalcogen atom on the cyclometalated chalcogenophene ring. The λ max (both in ethanol and adsorbed on TiO 2 ), frontier orbital level, and dye loading of thiophene-and selenophene-containing dyes are very close. Nevertheless, DUY24-Se has a higher molar absorption coefficient compared to DUY24; therefore, the DSC based on DUY24-Se has higher efficiency (8.4% under AM1.5 G one-sun and 26% under T5-light at ca. 6000 lux) than that sensitized with the DUY24 dye. These efficiencies are also higher than those (7.9 and 21.6%, respectively) of the cell dyed with N719, fabricated using the same conditions. The better performance of the device sensitized with DUY24-Se compared to DUY24-based cells suggests that selenophene is as good as (or even better than) thiophene to be a part of the cyclometalated ring for thiocyanate-free cycloruthenated sensitizers applied in DSCs. Furan-containing DUY24-O has much worse photovoltaic performance compared to the other two dyes. This is not only because DUY24-O has the shortest λ max , the lowest molar absorption coefficient, and the highest HOMO level but also the lowest dye loading (because of the strong interaction between the oxygen in furan and TiO 2 , the array of DUY24-O occupies more surface when adsorbed on TiO 2 ) and the fastest charge recombination. The physicochemical and photovoltaic properties as well as the adsorption behavior of the dye on the TiO 2 anode for the cycloruthenated sensitizers affected significantly by the chalcogen atom of the chalcogenophene on the cyclometalated ring provide a new strategy to design high-efficiency NCS-free cyclometalated sensitizers for DSCs.

Ruthenium‐based complex dyes for dye‐sensitized solar cells

“…TF21-24 (their structures are displayed in Figure 13) developed by Chi and coworkers [41] are the representative sensitizers. DSC dyed T A B L E 6 The photovoltaic parameter and dye-loading of DUY24-series sensitized cells as well as the optical properties of the sensitizers [36] Dye J SC (mA/cm 2 ) V OC (V) FF (%) η max (%) Dye-loading (mole/cell) λ max (nm) ε (Â10…”

“…To red‐shift the λ max of the dye molecules without sacrificing the dye‐loading, two cycloruthenated complexes, DUY24‐O and DUY24‐Se (their structures are shown in Figure 11) containing furan and selenophene moeities, respectively, were prepared. [ 36 ] DUY24‐O and DUY24‐Se (with similar size to DUY24 reported previously [ 33 ] ) were designed to reveal the function of the chalcogen atom in the cyclometalated ligand on the physicochemical and photovoltaic performance of the cycloruthenated sensitizers applied in DSC. The three sensitizers have a similar molecular size; therefore the effect of the molecular size on their photovoltaic performance can be negligible.…”

“…(a) The structure of DUY24‐O and DUY24‐Se (b) schematic representation of the DUY24‐O, DUY24, and DUY24‐Se dyes adsorbed on TiO 2 [ 36 ] …”