The Preparation Of Metal Sulfides/Carbon Flexible Composite Film And Application In Quantum Dot Sensitized Solar Cells

In recent years,flexible quantum dot sensitized solar cells?QDSSCs?have been widely studied for their advantages such as light,bendable,and easy to carry.Ti mesh has the advantages of good conductivity,high chemical stability,flexible and high temperature resistance.In this project,Ti mesh was selected as the conductive substrates of the counter electrodes in QDSSCs.Carbon materials?such as activated carbon,carbon nanotube,graphene,and so on?are widely used as catalytic active materials of counter electrodes in QDSSCs because of the easy preparation,stability and low costs.Another kind of active materials used in QDSSCs'counter electrodes is metal sulfides,such as PbS,Cu₂S,CoS,and NiS.The metal sulfides counter electrodes show high catalytic activity in polysulfide electrolyte.The composite counter electrodes based on metal sulfides decorated carbon might possess both the advantages of carbon and that of metal sulfides.we synthesized the metal sulfides?PbS and Cu_xS?decorated carbon nanotube?CNT?composite film on Ti mesh through in situ deposition of metal sulfides?PbS quantum dots and Cu_xS?by successive ionic layer adsorption and reaction technique?SILAR?.The composite counter electrode metal sulfides/CNT?PbS/CNT and Cu_xS/CNT?in our study showed excellent catalytic performance due to the synergistic effect between the CNT and metal sulfides?PbS quantum dots and Cu_xS?.The prepared metal sulfides/CNT?PbS/CNT and Cu_x S/CNT?CEs were assembled with CdS/CdSe co-sensitized TiO₂ electrode to prepare QDSSCs.In addition,we synthesized N-doped mesoporous carbon materials?N-MC?and prepared flexible N-MC/Ti counter electrodes.We synthesized the metal sulfides?PbS and Cu_xS?decorated N-MC/Ti composite film on Ti mesh.The main content of this project was substracted as follows:1.Firstly,we choosed Ti mesh as conductive substrates to prepare CNT/Ti flexible counter electrodes.The morphology and microstructure was investigated by SEM and TEM.It was found that the surface of the pure CNT film is well-distributed and smooth.PbS was decorated on the surface of CNT film through successive ionic layer adsorption and reaction technique.The quantity of the PbS quantum dots were regulated by controlling the number of the cycles of SILAR processes.The electrochemical catalytic activity of the PbS/CNT counter electrodes is investigated using cyclic voltammetry,electrochemical impedance spectroscopy and Tafel polarization curves.The results showed that the PbS quantum dots modification significantly improved the electrocatalytic activity of the CNT/Ti counter electrode.The process of the reduction of the S_n^2-ions was promoted and the charge transfer resistance of the counter electrode/electrolyte interface was reduced.The prepared PbS/CNT CEs were assembled with CdS/CdSe co-sensitized TiO₂ electrode to prepare QDSSCs.It was found that PbS quantum dots modification can significantly improve the photoelectric conversion performance of the solar cells.The fill factor and the open circuit voltage were improved.After optimization,the QDSSCs based on PbS/CNT counter electrodes show a photovoltaic conversion efficiency of 6.39%,which is improved by ca.40%than that of pure CNT CEs.2.Cu_xS was deposited on the surface of CNT through successive ionic layer adsorption and reaction technique.The quantity of the Cu_xS was regulated by controlling the number of the cycles of SILAR processes.The cycles of SILAR processes were regulated from 1 to 8 times.There were a large mount of agglomerated particles of Cu_xS.The agglomerated particles were inlayed in the pores of CNT.The electrochemical catalytic activity of the PbS/CNT counter electrodes is investigated using electrochemical impedance spectroscopy and Tafel polarization curves.The Cu_xS modification can significantly improve the photoelectric conversion performance of the solar cells because of the enhancement of the fill factor and open circuit voltage.The best PCE of the solar cells was ca.6.22%when the SILAR cycles were seven times.3.The polypyrrole was synthesized by the chemical polymerization of pyrrole.The prepared polypyrrole was carbonized to prepare N-doped mesoporous carbon materials?N-MC?and doctor-bladed on the Ti mesh to prepare N-MC/Ti flexible counter electrode.PbS and Cu_xS were modified on the surface of N-MC,separately.It was found that PbS and Cu_xS modification can both significantly improve the photoelectric conversion performance of the solar cells with the improvement of the fill factor,short circuit current density and open circuit voltage.