Study Of Cathode Doping And Interface Engineering Control To Achieve High-efficiency Lead Sulfide Quantum Dot Solar Cell

Solution-processable lead sulfide（PbS）quantum dot solar cells have developed rapidly in recent years with the highest device efficiency approaching 13%,attracting widespread attention.Compared with traditional solar cell devices,PbS quantum dot solar cell devices not only have stable performance,solution processability and low cost,but also have unique photoelectric properties such as size-dependent band-gap adjustment and multiple exciton effects,etc.As the improvement of solar cell device performance mainly relies on the increase of light absorption and charge collection,the device structure of PbS quantum dot solar cells has gradually changed from the initial Schottky junction,depletion heterojunction to a unique quantum junction structure.At present,for quantum junction devices,the main factors limiting the improvement of efficiency are the carrier recombination at the interface between the cathode zinc oxide（ZnO）as the window layer and the PbS layer,the carrier recombination among the boundaries of PbS quantum dots and the recombination at the interface between the PbS layer and the back electrode.This paper selects the Mg-doped ZnO（MZO）as the electron transport layer and focuses on the effects of energy level position,heat treatment temperature,Mg doping amount on the performance of the device.Moreover,the ZnO-NC/MZO is also used as the composite electron transport layer for eliminating suface defects.By optimizing the preparation process of the device,high-efficiency PbS quantum dot solar cell is realized.The main innovations of this thesis include the following two aspects:（1）Constructs Mg-doped ZnO electron transport layer for increasing the light transmittance,changing the band gap,improving the light collection efficiency,and reducing injection barriers at the cathode interface.The performance of the prepared PbS quantum dot solar cell（flip-chip device structure:tin oxide doped indium（ITO）/MZO/PbS quantum dot/Au）is much better than the control device with a structure of ITO/ZnO/PbS quantum dot/Au quantum dot solar cell.The energy conversion efficiency is increased from 4.59%to 5.52%.It is worth noting that the short-circuit current density of the device with the Mg-doped MZO is increased at a suitable annealing temperature.The device also shows good stability without obvious performance degradation after long-term storage in the atmospheric environment.The results have very good repeatability.（2）Design and synthesize ZnO nanocrystalline（ZnO-NC）to modify the interface between MZO and PbS quantum dots.On the one hand,it fills the defects of the MZO surface and reduces the defect density of the MZO film.On the other hand,compared to sol-gel ZnO,ZnO-NC has a good compatibility with the surface of quantum dots.It can decrease the work function of the MZO surface and reduce interfacial carrier recombination.Compared with the unmodified device,the short-circuit current density of the PbS quantum dot solar cell modified with ZnO-NC can be increased from 23.36 m A cm^-2 to 26.72 m A cm^-2,and the corresponding power conversion efficiency reaches 7.09%with an increase by 30%.To the best of knowledge,this is the first report in the literature that this kind of cathode interface modified quantum dot solar cell has been achieved.In general,we obtained PbS quantum dot solar cells with better performance through cathode doping and interface modification regulation,which provides a new way to improve the performance of solution-processed PbS quantum dot solar cells in the future.