Study On The Optimizing Photovoltaic Performace Of Quantum Dots Sensitized ZnO Solar Cells Via Interface Modification And Cosensitization

Quantum dots sensitized solar cells(QDSSCs)become one of third generation solar cells with promising application potential due to their low cost and high theoretical conversion efficiency.However,the power conversion efficiency of QDSSC is always lower than that of dye-sensitised solar cells(DSSCs)due to its low quantum dots loading amount,high interface electronic-hole recombination rate and narrow apectral response region.The surface modification and cosensitization are effective approaches to improve the photoelectric conversion efficiency of QDSSCs.Hence,on one hand,we chose appropriate self-assembled monolayers(SAMs)to modify the interface of ZnO/ZnS heterostructure photoanode.On the other hand,we ultilized double quantum dots to cosensitize the photoanodes.We investigated their effects on the photovoltaic performance of QDSSCs and revealed the relative influence mechanism.The obtained innovative results are listed as follows:To adjust the energy level alignment of ZnO/ZnS heterostructure photoanodes and improve the photoinduced carrier transport efficiency,we introduced 3-PPA into ZnO/ZnS heterostructures interface by simple chemical immersion process.We investigated the effects of 3-PPA immersion time on the photovoltaic performance of ZnO/ZnS heterojunction QDSSCs.The results indicate that 3-PPA actually serve as a buffer layer in ZnO/ZnS heterostructure to lower the energy barrier formed by ZnS.This new energy barrier can not only work efficiently on retarding the back transfer of electrons,but also weaken the blocking effect on the charge injection process,which finally results in the enhancement of photoelectric conversion efficiency.To exend the optical absorption range,we firstly deposited the CdS quantum dots on the surface of ZnO nanorods by the successive ionic layer adsorption method(SILAR).Then we in-situ transformed a part of CdS QDs into CdSe QDs with anion exchange method.Subsequently,we fabriated CdS@CdSe cosensitized solar cells and investigated the effects of replacement temperature and replacement time on the photovoltaic performance of solar cells.The results indicated the photoelectric transformation efficiency of consensitized QDSSCs reached the maximum with anion exchange for 24 h under 80 oC.The UPS resultsrevealed that CdS@CdSe cosensitization can adjust the electronic band structure,extend the optical absorption range and suppress the blocking effects during the electron transportation process,which finally resulted in the enhancement of photovoltaic performance.To further protect the CdS@CdSe QDs layer,we deposited ZnS layer on the surface of CdS@CdSe QDs layer with SILAR method and investigate the effects of depositing cycles on the photovoltaic performance of CdS@CdSe QDSSCs.When we deposited ZnS layer for 3 cycles,the photoelectric conversion efficiency can reach 1.06%.