The Assembly Of Vanadium(Ⅳ)-Substituted Keggin-type Polyoxometalate/Graphene Nanocomposite And Its Application In Photovlotaic System

Polyoxometalates(POMs) can undergo a stepwise multi-electron reversible redox process without any structure changes. In addition, the absorption spectrum of the POMs can be regulated by introducing multiple transition metal elements, which can even cover as much as the whole UV-Visible light spectrum. Due to those high stability and advantageous physicochemical properties, POMs have exhibited promising application as the photosensitizer of the Dye-sensitized solar cells(DSSCs). But up to now, most of POMs are not introduced into the solar photovoltaic system as sensitizer of DSSCs, owing to less of the anchoring groups to strongly bind the POMs onto the semiconductor surface and their lower LUMO levels than Ti O2. Furthermore, POMs are usually acted as the electron acceptor in the solar photovoltaic system.In this paper, Si W11V/graphene nanocomposite is prepared by a simple chemical reduction approach at room temperature, which is a facile and friendly environmental method. The Si W11V/graphene nanocomposite was firstly introduced into the Ti O2 film, and the films showed a significant photocurrent response. The photocurrent responses of the films are highly dependent on the mass of Si W11 V clusters on graphene, the photocurrent increases gradually with the increasing of the mass of Si W11 V clusters. This is due to the following points. 1. After the chemical reduction, there are still some oxygen-containing functional groups attach on both sides of graphene, which can help to contact with Ti O2 nanoparticles. 2. Although graphene is a semiconductor, it has an unusual feature that its band gap is exactly zero. The energy level of graphene is close to FTO, and the 2D graphene behave as an electron transfer channel, which brought a faster electron transport. 3. Si W11 V has an appropriate band gap, which can be excited by nearly the whole UV-Visible light spectrum, it can be an electrons donor. The LUMO of Si W11 V is higher than the energy level of graphene. So the excited electrons of Si W11 V can be captured and transported to the FTO rapidly and effectively through the graphene bridges under illumination. On the other hand, Si W11 V also act as an electron acceptor and play the role of electron mediator to accelerate the electron transmission and suppress the carrier recombination since the LUMO of Si W11 V is lower than the CB of Ti O2. In this system, Si W11 V not only acts as an electron acceptor, but also as a sensitizer(electron donor) which has a lower energy level than the CB of Ti O2.