| The global energy crisis brought about by the exhaustion of fossil fuels makes people gradually realize the importance of developing renewable energy such as solar energy,wind energy,tidal energy and water energy.Solar energy is a kind of clean energy with abundant reserves among them,so the development and utilization of solar energy has become a hot topic of research in various countries and regions.Quantum dot sensitized solar cells(QDSCs)are an extension and development of dye-sensitized solar cells,which use quantum dots instead of molecular dyes to realize direct conversion from solar energy to electric energy and have the advantages of low cost and simple production process.Due to the multi-exciton effect of quantum dots,the theoretical conversion efficiency of quantum dots sensitized solar cells can reach 44%.In this paper,the quantum dots were heat treated and the photoanode was passivated to suppress the charge recombination inside the solar cell.At the same time,a kind of stable,efficient and easy-to-make counter electrode is explored to improve the conversion efficiency of quantum dot sensitized solar cells.(1)Heat treatment of CdSeTe quantum dots means that the quantum dots purified by centrifugation are dispersed in the mixed solution of dichlorethane and oleoamine and after heat treatment at 180? for a period of time in an inert atmosphere,precipitation centrifugation is carried out.After 8h heat treatment,the size of CdSeTe quantum dots basically remain unchanged,while the crystallinity is significantly enhanced and the lattice stripes are more obvious.The reduction of suspended bonds on the surface makes the quantum dots more stable and the sensitization has stronger light absorption on the titanium dioxide.At the same time,in order to alleviate the lattice mismatch between the quantum dot sensitized photoanode and the ZnS passivation layer,we introduce the passivation layer between them.It is found that the introduction of Mn-CdSeS passivation layer can inhibit the charge recombination at the interface between the photoanode and the electrolyte,and the doping of transition metal can improve the short-circuit current density.The experimental results show that the heat treatment of quantum dots and the introduction of passivation layer can effectively inhibit the charge recombination inside the cell,and thus improve the conversion efficiency of solar cells.The optimized CdSeTe QDSCs have a short-circuit current density(JSC)of 20.45 mA/cm2 and an open-circuit voltage(VOC)of 0.585V,and the cell conversion efficiency can reach 6.88%,which has increased by nearly 53.2%.(2)C-N/Ti counter electrode was obtained by electrodeposition of PPy on Ti foil and then annealing at high temperature.This kind of counter electrode has the advantages of simple fabrication method,strong stability and good performance.By controlling the length and thickness of the C fiber deposited on the Ti foil,the short-circuit current of the battery assembled with C-N/Ti counter electrode can reach 20.35mA/cm2,the open-circuit voltage is 0.624V,the fill factor is 0.578,and the PCE is 7.343%.In addition,in order to increase the catalytic activity of the counter electrode and further improve the conversion efficiency of the quantum dot sensitized solar cells,a layer of CuS is deposited on the C-N/Ti counter electrode using the SILAR method.The short-circuit current of the solar cell assembled with such counter electrode is 21.31 mA/cm2,the open-circuit voltage is 0.63 V,the fill factor is 0.586,and the conversion efficiency can reach 7.865%.The conversion efficiency has increased by 14%compared with the commonly used solar cells assembled with CuS/latten counter electrode. |
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