Preparation And Performance Optimization Of The Counter Electrode For Quantum Dot Sensitized Solar Cells

The world is facing severe energy shortage and increasingly serious environmental pollution in recent years,so it is essential for researchers to look for a environment-protective,renewable energy to replace traditional fossil energy.Solar cell is the most efficient method to use solar energy directly.Due to the high absorption coefficient and multiple exciton effect of quantum dots,Quantum dot sensitized solar cells?QDSSCs?have a high conversion efficiency in theory.However,the actual conversion efficiency is much less than the theoretical efficiency.Counter electrode?CE?plays an important role inthe stability and high efficiency of QDSSCs,and the photovoltaic performance of solar cell is partly determined by the electric and catalytic activity of the counter electrodes.This paper prepared TiO₂ photoanode by the doctor-blade method,the CdS quantum dots?QDs?and CdSe QDs sensitized TiO₂ photoanode was fabricated using successive ionic layer adsorption and reaction?SILAR?method and chemical bath deposition?CBD?method,respectively.Finally,ZnS passivation layer was deposited by SILAR method.Then inject polysulfide electrolyte in the middle of the photoanode and CE,and prepared and investigated the CEs of single metal sulfides and composite metal sulfides,Cu₂S and RGO/Cu₂S,which were used to improve the photovoltaic conversion efficiency?PCE?of the QDSSCs.The main contents of this paper are summarized as follows:1.The CuS/CoS,CuS/NiS,CuS,CoS and NiS CE were deposited on FTO conducting glass by a simple chemical bath deposition method,which were used to investigate the effect of the different single metal sulfides and composite metal sulfides CE on performance of cells.The results showed that the improved cell efficiency was attributed to the excellent electrical conductivity and catalytic activity of CuS and CoS,respectively,and combination of different metal sulfide composites could increase open-circuit voltage(V_oc)value without sacrificing the short-circuit current(J_sc),the cell with CuS/CoS CE achieved best power conversion efficiency???of 5.22%.2.The Cu₂S CE was made by etching,and it was used to study the effect of the heating time on copper sheet using hydrochloric acid and the reaction time between copper sheet and sodium polysulfide solutionon performance of cells,respectively.The results showed that the power conversion efficiency of 3.27%was achieved by Cu₂S CE in the conditions that the pretreatment time using hydrochloric acid is 30min,and reaction with sodium polysulfide for 20s under 70?.3.Graphene oxide was made using natural graphite powder through a Hummers'method.By adjusting the content of graphene oxide in different proportions,reduced graphene oxide?RGO?/Cu₂S composite were fabricated with a facile one-step solvothermal process.The results showed that when adding 12mL of graphene oxide,the open circuit voltage,short circuit current density and fill factor of QDSSCs were all increased,and an efficiency of 4.76%was achieved.Moreover,the experiment proved that adding graphene oxide also can improve the power conversion efficiency of QDSSCs.