N, S, P‐Hybrid Donor–π–Acceptor Organic Dyes for Dye‐Sensitized Solar Cell: Synthesis, Optical Properties, and Photovoltaic Performances. Issue 6 (14th July 2014) - Matano, Yoshihiro
ABSTRACT New donor–π–acceptor organic (D–π–A) dyes composed of triarylamine, oligothiophene, and phosphole subunits were prepared, and their optical and photovoltaic properties were investigated. The regioselective α‐lithiation of the thiophene ring of 2‐(thiophen‐2‐yl)phospholes bearing an ester group, followed by treatment with tributyltin chloride afforded 2‐(5‐(tributylstannyl)thiophen‐2‐yl)phosphole derivatives, which underwent Stille coupling with 5′‐(p‐(diarylamino)phenyl)‐5‐bromo‐2, 2′‐bithiophene to give triarylamine–terthiophene–phosphole hybrid π systems bearing the terminal ester group. The alkaline hydrolysis of the ester group yielded the target dyes, bearing the carboxylic acid anchoring group. The UV–vis absorption spectra of the new N, S, P‐hybrid dyes displayed broad and intense π–π* transitions with two absorption maxima in the visible region. Density functional theory (DFT) calculations of two dye models revealed that each highest occupied molecular orbital (HOMO) resides on the triarylamine–oligothiophene π network, whereas each lowest unoccupied molecular orbital (LUMO) is basically located on the phosphole subunit. In addition, the time‐dependent DFT calculations of the models showed that the lowest energy bands of these hybrid dyes are mainly consisted of the HOMO‐to‐LUMO+1 and HOMO‐to‐LUMO transitions with the large intramolecular charge‐transfer character. The N, S, P‐hybrid‐dye‐sensitized TiO2 cells exhibited moderate power conversion efficiencies of up to 5.6%. The present findings corroborate the potential utility of the phosphole skeletons as the acceptor components in the D–π–A sensitizers.