Investigation On Aqueous-Processed Nanocrystal Solar Cells And Their Properties

Aqueous-solution-processed solar cells have attracted great interest in recent years due to their excellent properties of easy processing,large area production and low-cost fabrication.However,during fabricating the device,most cases involve in the use of highly toxic solvents such as chloroform and toluene,which have an adverse effect on the environment.Therefore,the development of aqueous solution processing method to fabricate solar cells is of great significance.The use of aqueous solution as a solvent to prepare nanocrystals?NCs?solar cells has the advantages of clean,non-toxic and inexpensive with performance continuously improving.However,the leakage current and the interfacial recombination existed in the devices are two issues to be addressed,which severely limit the performance of devices.In order to solve the above problems,this thesis mainly carried out the following work:?1?Aqueous-processed NCs solar cells doped with insulating polymer.Thermostable insulating polymer poly?vinyl pyrrolidone??PVP?was incorporated into aqueous CdTe NCs for fabricating special hybrid solar cells with structure of ITO/TiO₂/CdTe/PVP:CdTe/MoO₃/Au.Power conversion efficiency?PCE?of 4.60%was achieved in PVP:CdTe device by regulating the mixing ratio of PVP to CdTe,which was superior to the pure CdTe device.The function of PVP was to fill the voids among CdTe NCs to decrease the leakage current and reduce the contact area between CdTe and MoO₃ to suppress the interfacial recombination.The introduction of excessive PVP hindered the charge-carrier transport,which led to worse performance.Therefore,the relationship between the thickness of the active layer and the content of PVP was further systematically studied.It was found that more PVP content was needed in the devices with thin active layer while less PVP content was needed in the devices with thick active layer in order to achieve the desired effect.?2?Aqueous-processed NCs bulk heterojunction?BHJ?solar cells doped with insulating polymer.On the basis of?1?,in order to further improve performance of the device,the electron transport layer was changed from TiO₂ to ZnO,inserting a Zn O:CdTe BHJ layer between the electron transport layer and the active layer.The structure of solar cell was ITO/ZnO/ZnO:CdTe/PVP:CdTe/PVP:CdTe/MoO₃/Au.Meanwhile,the annealing temperature was increased to 400^oC to improve the carrier mobility.Through systemically regulating the thickness of the active layer,the PCE of 5.84%was achieved that was improved 58.7%in comparison with that of the pure CdTe device.In-depth mechanism studies showed that the constructed Zn O:CdTe BHJ extended the depletion region width from 150 to 174 nm,enhancing carrier transport rate and promoting carrier extraction to improve the device performance.Currently,this PCE was the highest efficiency based on insulating polymer-modified NCs solar cells.