Research Of The Relationship Between The PbS Quantum Dot Chemical Composition And The Corresponding Solar Cell Photovoltaic Performance

Quantum dot solar cells?QDSCs?have emerged as a promising candidate for the third-generation solar cells.PbS QDs were widely used in the preparation of QD solar cells due to it's large Bohr radius of 18 nm,size-tunable band gaps,high absorption coefficient of 1-5×10⁵ cm^-1 and multiple exciton generation.For the PbS QD sensitized solar cells,the chemical composition of PbS QDs strongly effect the photovoltaic performance of corresponding solar cells.In this dissertation,PbS QD was deposited on the TiO₂ nanorods array with the length of 600 nm,diameter of 20 nm,areal density of500?m^-2 using spin-coating assisted successive ionic layer adsorption and reaction?spin-SILAR?.PbS quantum dots with different chemical compositions were prepared by changing the composition of the precursor solution,and the influence of the chemical composition of PbS quantum dots on the photovoltaic performance of TiO₂ nanorod array sensitized solar cells was studied.PbS-S₂^2--EDT quantum dots were prepared on the TiO₂ nanorod array using a three-step spin-SILAR by introducing polysulfide anion(S₂^2-)in the Na₂S precursor solution.PbS-S₂^2--EDT quantum dots were analyzed using SEM,XRD,UV-vis-NIR.When the concentration of S₂^2-in the precursor solution increased from 0 mmol×dm^-3 to 0.001mmol×dm^-3 and 0.002 mmol×dm^-3,the loading quantity of PbS-S₂^2--EDT quantum dot on the TiO₂ nanorod array and the crystallinity and average crystallite sizes of the PbS-S₂^2--EDT quantum dots increased.Comparing the photovoltaic performance of the corresponding solar cells,when the concentration of S₂^2-in the precursor solution was0.001 mmol×dm^-3,the PCE of the corresponding solar cell was 4.25%,which was higher than 3.88%and 3.68%for the concentration of S₂^2-in the precursor solution was 0mmol×dm^-3 and 0.002 mmol×dm^-3.PbS-SCN^--EDT quantum dots were prepared on the TiO₂ nanorod array by spin-coating of 0.005 mmol×dm^-3 Pb?NO₃?₂ and a mixed solution containing Na₂S,SCN^-,and EDT.The influence of Na₂S concentration in the mixed solution on the crystal phase,optical band gap,morphology and chemical composition of the PbS-SCN^--EDT quantum dots were investigated.It was found that when the concentration of Na₂S decreased from0.002 mmol×dm^-3to 0.0015 mmol×dm^-3,the average crystallite sizes of quantum dots decreased,the absorption offset exhibited a blue-shift,the band gap increases,and the relative content of Pb-EDT increased.The PCE increased from 3.69%to 4.03%.The gradient-band-gap PbS-SCN^--EDT quantum dot sensitized solar cell achieved a PCE of 4.55%.In addition,the preparation of Sb₂S₃ thin film by a low-pressure solvothermal method was studied.The obtained Sb₂S₃ film was analyzed using SEM,XRD,and UV-Vis.It was found that the thickness of Sb₂S₃ film was 200 nm,the film surface was flat and crystal size was uniform and tightly connected.When the Sb₂S₃ film was annealed at300°C for 5 min,the Sb₂S₃ film changed from amorphous to stibnite crystalline phase,and the absorption offset widened from 555 nm to 735 nm,the corresponding band gap decreased from 2.23 eV to 1.69 eV.The assembled planar Sb₂S₃ solar cell obtained the PCE of 1.67%.