Synthesis of copper(II)–imidazole complex modified sandwich-type polyoxometalates for enhancing the power conversion efficiency in dye-sensitized solar cells

Abstract

A inorganic–organic hybrids based on copper(II)–imidazole complex modified sandwich-type tungstoantimonite H6[Cu(im)4][Na2Cu3(H2O)3Cu(H2O)2(SbW9O33)2]·36H2O (1) (im = imidazole) was hydrothermally synthesized and characterized structurally by single crystal X-ray diffraction analysis. Its central band is composed of four Cu2+ and two Na+ forming a rare plane hexagon, and the sandwich-type anions [Na2Cu3(H2O)3Cu(H2O)2(SbW9O33)2]8- are further joined into a one-dimensional chain by a [Cu(im)4]2+ cation. The Kubelka-Munk function F and electrochemical cyclic voltammetry (CV) indicate that the energy level of 1 match well with the conduction band of TiO2, and compound 1 can act as an electron acceptor to accelerate the transfer of electrons. The UV–vis absorption Spectra of 1 has a wide range, and the absorption range of TiO2 can be extended to the visible region to improve the light absorption of TiO2 after doping with TiO2. The incorporation of 1 into TiO2 as the photoelectrodes of Dye-sensitized Solar Cells (DSSCs) improves the Jsc (the short circuit current density) and PCE (the power conversion efficiency) of DSSC, the DSSC assembled with 5%1@TiO2/P25 photoelectrodes has the best performance and its Jsc and PCE is 17.54 mA cm−2 and 7.71% respectively, the improvement of the efficiency is 26.8% compared with pure P25 (6.08%). In addition, electrochemical impedance spectroscopy and open circuit voltage decay show that 1 can promote electronic transfer, suppress charge recombination, and extend electronic lifetime.