The Synthesis And Functional Applications Of Polyoxometalate-based Photoelectrical Materials

Solar energy is an ideal renewable energy. Dye-sensitized solar cells(denoted as DSSCs) have attracted intensive attention by international scholars owing to their ease fabrication, stable performance, low cost and environmental friendliness. To date, their development objectives should focus on the issues of increasing photoelectrical energy conversion efficiency, decreasing device cost and improving long-term stability. So it is imperative to develop cheap and superior photoelectrical materials for pushing the scale-up application of DSSCs. Polyoxometalates(called as POMs) represent a class of natural nanoscale metal-oxygen clusters based on abundant elements composition with excellent photoelectrochemical properties and high stability, which have enormous potential applications in photovoltaic cells. In this paper, three cases of novel open-chain carboxyethyltin decorated sandwich-type germanotungstates have been successfully designed and synthesized. They were firstly applied into DSSCs to efficiently enhance the photovoltaic performance after compositing with Ti O2 and single-walled carbon nanotube, respectively. In addition, the first systematic study was conducted to understand the energy band structures of a series of POMs. Moreover, the application of isopolyoxoniobate in Zn O-based DSSCs was preliminarily explored.1. A novel sandwich-type germanotungstate [C(NH2)3]10[Mn2{Sn(CH2)2COOH}2(B-α-Ge W9O34)2]·8H2O(Ge W9-Mn-Sn R) was designed and synthesized in aqueous solution; it represents the first case of single crystalline POM compound functionalized by open chain carboxyethyltin; its optoelectronic properties were explored through fluorescence spectrum(FL), surface photovoltage spectrum(SPV), electrochemical method and solid diffuse spectrum. The preliminary attempt of applying Ge W9-Mn-Sn R for sensitizing Ti O2 to fabricate DSSCs resulted in the final performance enhancement. After synthesizing Ge W9-Mn-Sn R/Ti O2 composite and adsorbing N719 to assemble a co-sensitized electrode, the photoelectrical conversion efficiency of DSSCs was improved by enhancing absorption spectra and accelerating the electron transfer. This is the first time to introduce POMs with two arms into DSSCs.2. Two new open-chain carboxyethyltin decorated sandwich-type germanotung- states {C(NH2)3}10H2[Cu2{Sn(C3H4O2)}2(B-α-Ge W9O34)2]·7H2O(Ge W9-Cu-Sn R) and {C(NH2)3}10H2[Co2{Sn(C3H4O2)}2(B-α-Ge W9O34)2]·8H2O(Ge W9-Co-Sn R) have been successfully synthesized. They can markedly increase the electrocatalytic activity of single-walled carbon nanotube toward triiodide reduction when assembled into composite electrodes, which have shown a conversion efficiency of 6.32% that is comparable to that of Pt electrode(6.29%) when used as counter electrodes in DSSCs.3. With the assistance of K7HNb6O19, Zn O polyhedra was successfully synthesized through a simple solvothermal route in an alkali solution; the photoelectrical property of Zn O polyhedra was investigated after fabricating the photoanodes to assemble DSSCs; the influence of post-treatment by Ti Cl4 on the photovoltaic performance of Zn O-based DSSCs was explored.4. The energy band structures of a series of POMs were systematically investigated by the photoelectrochemical methods in depth for the first time, including the typical saturated Keggin and Dawson structure, the lacunary and transitional metal substituted structure; the energy levels of their highest occupied molecular orbital(HOMO) and lowest unoccupied molecular orbital(LUMO) have been systematically compared with that of Ti O2; we believe this basic work can provide guidance for exploring multifunctional application of POMs in diverse optoelectonic devices.