Preparation And Photovoltaic Properties Of Transition Metal Sulfide Nanosized Films

As one of the third-generation solar cells,dye-sensitized solar cells(DSSC)have high photoelectric conversion efficiency(PCE)and low cost,which will facilitate its large-scale production.Counter electrode is an important part of the dye-sensitized solar cell.The electrocatalytic performance of the counter electrode will affect the reduction of ion pairs in the electrolyte,which in turn affects the photoelectric conversion efficiency of DSSC.Platinum(Pt)is the most commonly used counter electrode material for dye-sensitized solar cells because of its highly efficient electrocatalytic ability and conductivity.However,the high cost of Pt limits the commercial application and large-scale production of DSSC.In addition,Pt will react with the electrolyte,which affects the stability of DSSC.Therefore,it is necessary to find effective Pt-free counter electrode materials to solve the problem.As an effective Pt-free counter electrode material,transition metal sulfides have received extensive attention in the DSSC research field for their excellent electrocatalytic performance.Researchers indicate that heterojunctions formed by different types of transition metal sulfides can further improve their electrocatalystic properties.In this paper,two transition metal sulfide heterojunction films were prepared and used as counter electrodes of DSSCs.The specific research is as follows:(1)Preparation of heterojunction films of MoS₂/NbS₂ and their properties as DSSC counter electrodes.MoS₂film,NbS₂film and heterojunction films composed of MoS₂/NbS₂and NbS₂/MoS₂are prepared on FTO conductive glass substrate by pulsed laser deposition(PLD)and vapor-phase sulfurization.The obtained films are used as the counter electrodes of dye-sensitized solar cells and to test their photovoltaic performance.The results show that the heterojunction electrode with the MoS₂/NbS₂/FTO structure exhibits the highest photoelectric conversion efficiency in the DSSC test.The MoS₂on the surface directly contacts with the electrolyte and accelerates the reduction reaction of the redox couple.The NbS₂in the lower layer of the film accelerates the electrons transformation from the conductive substrate.The heterojunction interface between the two promotes the electron transport in the counter electrode.The above mechanism accelerates the reaction process of DSSC at the counter electrode from many aspects,thereby improving the photoelectric conversion efficiency of the DSSC.The abundant reserves and low price of transition metal sulfides make up for the lack of Pt,and molybdenum sulfide is not easy to react with the electrolyte,thereby improving the stability of the DSSC.(2)Preparation and photovoltaic properties of heterojunction films of NiS₂/MnS as DSSC counter electrodes.Transition metal sulfides are an important alternative to Pt in dye-sensitized solar cells to lower the cost and improve the stability.In this thesis,NiS₂/MnS and MnS/NiS₂heterojunction films were deposited on FTO as the counter electrode(CE)by pulsed laser deposition(PLD)and vapor-phase sulfurization.The heterojunction CE of NiS₂/MnS can achieve a power conversion efficiency of 6.44%,which is close to that of the Pt CE(6.84%).The unique band gap structure of NiS₂and MnS in this heterojunction can accelerate the transport of electrons in the CE to improve the ability of electro-catalysis.This makes the heterojunction film composed of two inexpensive transition metal sulfides an ideal substitute for Pt film.