Modification Studies On ZnO/ZnS/CdS Nanotubes Quantum Dot Sensitized Solar Cells

To replace fossil energy,new energy and energy conversion storage devices have triggered a research boom.Among which solar cells have been greatly developed.On the basis of dye-sensitized solar cell(DSSC),quantum dot-sensitized solar cell(QDSSC)have entered the researcher's field of vision and become a promising solar device with advantages of low costs and high conversion efficiency.Selenium sulfur metal compounds(PbS,CdS,CdSe),as quantum dot(QD)substituted the traditional dye molecules depositing on the semiconductor mesoporous films with wide band gap,such as TiO2,ZnO,SnO2,which forms the basic structure of QDSSC.Compared with the conventional TiO2,ZnO with a large carrier mobility is easy to prepare,and exhibits good photoelectric performance and stability as an electron transport layer.Among various nanostructures,one-dimensional(1D)structure can provide a carrier fast transmission channel and improve the photo-generated electron scattering rate,which is favorable for electron transport and reduction of electron-hole recombination.Although zinc oxide-based QDSSC has made great progress in recent years,it is still limited by a narrow range of light absorption,and the compounding is relatively serious,which causes low efficiency.Therfore,in order to improve the photoelectric conversion efificiency(PCE),researchers have attempted to combine the high photon conversion utilization of cadmium quantum dots(QD)and width absorption of lead quantum dot to prepare composite quantum dots,such as CdSeTe QD whose energy level structure is controlled by band coupling,which is more conducive to electron injection.Another strategy for reducing losses is to cover the photoanode with a wide bandgap material and form a high barrier layer,reducing the surface electronic state density and electron concentration on the surface,and suppressing charge loss,such as the introduction of a ZnS/SiO2 layer.Based on the previous work on ZnO/ZnS nanotubes,the study attempted to prepare CdS QD by ion exchange method and it discussed the effect of preparation temperature on the properties of QDSSC assembled by ZnO/ZnS/CdS NT.Mn doping CdS at an optimum temperature of 110 ? was prepared to improve device performance.In addition,this study also attempted to introduce ZnS-MnS composite passivation layer between the ZnO electron transport layer and the CdS QD by a one-step method,adjusting the energy level structure of the photoanode.The specific research work is as follows:(1)QDSSC assembled with ZnO/ZnS/CdS NT and ZnO/ZnS/Mn-CdS NT arrays was prepared.The ZnS barrier layer and CdS QD were prepared by using ion exchange method.By discussing the deposition temperatufe of CdS QD,the optimal condition is 110 ?,which promotes the ion exchange reaction,obtaining a uniform CdS QD,and avoids the formation of a thin ZnS barrier layer at too high temperature,both short-circuit current(Jsc)and open circuit voltage(Voc)were significantly improved,achieving an efficiency of 2.33%.Then,the Mn element was introduced into the CdS QD by in-situ doping,the photoanode level structure was adjusted,the electron capture efficiency was improved,and the recombination between the partial holes and the oxidized polysulfide electrolyte was also suppressed.The concentration was optimized to obtain an optimum efficiency of 2.61%.(2)The QDSSC assembled by ZnO/ZnS-MnS/CdS NT array was prepared for the first time.ZnS-MnS composite passivation layer was successfully synthesized by one-step method.After the introduction of the MnS layer,its higher conduction band effectively hinders the reverse transmission of electrons and reduces the recombination of photogenerated carriers.In addition,the uniform ZnS-MnS composite barrier layer effectively blocks the direct contact between the polysulfide electrolyte and the electron transport layer,and reduces the recombination of electron-hole pairs.At the same time,the formation of the MnS barrier layer also increases the load of the CdS QD,improving the light absorption intensity in the visible light region.After the introduction of MnS layer,PCE increased from 2.33%to 3.72%,and both Jsc and Voc were significantly improved.