N,S,P-Hybrid Donor-π-Acceptor Organic Dyes for Dye-Sensitized Solar Cell: Synthesis, Optical Properties, and Photovoltaic Performances

New donor-pi-acceptor organic (D-pi-A) dyes composed of triarylamine, oligothiophene, and phosphole subunits were prepared, and their optical and photovoltaic properties were investigated. The regioselective alpha-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 pi 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 pi-pi* transitions with two absorptionmaxima 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 p 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 exhibitedmoderate 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-pi-A sensitizers. (C) 2014 Wiley Periodicals, Inc.