Quantum Dot Sensitized Solar Cells Based On Metal Chalcogenide-counter Electrodes

Among the next generation of new-type photovoltaic devices,quantum dot sensitized solar cells(QDSCs)have attracted much attention and shown great potential because of their excellent features of high theoretical photoelectric conversion efficiency,simple preparation and low cost.A QDSC is mainly composed of a photoanode,an electrolyte and a counter electrode(CE).As the key component of device,the catalytic activity and stability of CEs directly affects the overall photovoltaic performance of QDSCs.At present,platinum(Pt)and cuprous sulfide(Cu2S)counter electrodes are widely used.However,the Pt CE is expensive and involves a poisoning effect in polysulfide electrolyte,which will greatly reduce the catalytic activity of Pt;although the Cu2 S CE shows high reduction activity for the regeneration of the polysulfide electrolyte,it involves continuous corrosion and poor mechanical stability in conjunction with polysulfide electrolytes.Therefore,the development of high-performance CE materials is of great urgent.In the first chapter,the relevant background knowledge of this paper is mainly introduced.The research progress and the main issues of QDSCs are reviewed.In particular,in view of the high catalytic activity of metal chalcogenides,the use of two types of metal chalcogenide CEs,i.e.,lead sulfide(Pb S)and copper selenide(Cu3Se2,Cu2-x Se)films,for QDSC applications is studied,aiming to construct high efficiency photovoltaic devices.In the second chapter,the preparation process of CdS/CdSe quantum dot co-sensitized Ti O2 solar cells,as well as material characterization and device measurements are introduced.In the third chapter,Pb S nanocubics were directly deposited on FTO conductive substrates by chemical bath deposition(CBD)method.The crystal structure,morphology and optical properties of Pb S nanocrsytals were studied.The results show that the Pb S nanocrystalline film has a cubic phase crystal structure with high crystallinity and a uniform distribution of cubic morphology.The as-prepared Pb S films were used as CE to assemble Cd S/Cd Se sensitized Ti O2 solar cells.The photovoltaic performance revealed that the Pb S CE exhibited comparable electrocatalytic activity to the traditional Cu2 S CE,which was significantly high thanthe noble metal Pt CE;meanwhile,Pb S CE can solve the stability issue of the Cu2 S CE in the polysulfide electrolytes.As a result,Pb S thin films with high catalytic activity,high stability and simple preparation are expected to serve as promising candidates for the CEs of QDSCs.In the fourth chapter,highly crystalline copper selenide films were obtained on the FTO conductive substrates by potentiostatic electrochemical deposition.Direct annealing or selenization annealing treatment in an inert gas induces a phase transition from tetragonal Cu3Se2 to cubic Cu2-x Se.The photovoltaic measurements revealed that the non-stoichiometric Cu2-x Se film prepared by direct annealing treatment showed better electrochemical catalytic activity,mainly benefitted from a large number of active reaction sites and an effective charge transport path from the microstructure of Cu2-x Se film provided.Meanwhile,the Cu2-x Se films also exhibited comparable catalytic activity to the conventional Cu2 S CEs and higher catalytic activity than Pt CEs.The results show that the copper selenide CEs can be used to construct high performance QDSCs.