Microscopic Mechanism On Graphene Enhanced Photovoltatic Efficiency Of Dye-sensitized Solar Cells

Dye-sensitized solar cell(DSSC)is a new type of photovoltaic devices,which have attracted extensive attention of researchers because of their low cost,simple fabrication,high efficiency,green and pollution-free.Since Gr?tzel first reported DSSCs in 1991,it has achieved 13% photoelectric conversion efficiency,but from the perspective of practical application,the photoelectric conversion efficiency of photovoltaic device still needs to be further improved.A deep understanding of the components and working mechanism of DSSC is of great significance for improving the photoelectric conversion efficiency.Titanium dioxide nano-films in photoanode are the core part of DSSCs,which has an important influence on charge transfer and battery performance.In this paper,the microscopic mechanism on graphene enhanced the photovoltaic efficiency of DSSC is deeply explored from a theoretical point of view.Because the graphene in practical application is not perfect,there are some defects such as holes and impurities.So we consider the effect of a series of functionalized graphene on its photoelectric conversion efficiency.The relevant research contents are as follows:1.In Chapter 4,we clearly answer the question why graphene coating on the semiconductor layer can enhance the photoelectric conversion efficiency of a DSSC from theoretical perspective.Several arrangements of the graphene layer on the substrate model of titanium dioxide surface are carefully studied and discussed.The dynamic interfacial electron propagations are simulated with consideration of the underlying nuclear motion effect.Theoretical investigation shows that graphene can speed up the electron injection from the LUMO orbital of dye molecules into the semiconductor layer and play the role of electron transport layer only if C atoms in graphene layer form C-Ti bands with five-coordinated Ti atoms in titanium dioxide.Additionaly,if the graphene sheet covers the Ti O2 surface in parallel,the free electron on graphene can only hop onto the Ti O2 surface in a relative long tunneling period.Therefore,graphene in this case mainly takes the role of a shielding layer for preventing the recombination of the electrons injected in Ti O2 and the electron holes remaining on the dye molecules or in the electrolyte,but also to shield the injection of exciting electrons.2.In Chapter 5,we further explore the effect of oxygen-containing functional groups in graphene oxide(GO)on photogenerated electron injection.By designing some simplified models,the interfacial electron transfer(IET)between the dye molecule CC,graphene oxide and anatase titanium dioxide(101)surface was simulated,which clearly explained that the oxygen-containing functional groups in graphene oxide(GO)could not provide an effective channel for the injection of photogenerated electrons.3.In Chapter 6,we further explore the effect of B/N doped(oxidized)graphene on electron injection from a theoretical perspective.A series of simplified models were constructed to simulate the interfacial electron transfer(IET)between the dye molecule CC,B/N doped graphene and anatase titanium dioxide(101)surface.It clearly understood that the nanocomposite composed of doped graphene and titanium dioxide could also transmit photogenerated electrons and improve the photoelectric conversion efficiency of DSSC.