The Preparation Of PbI₂ And PbS Nanosheets And Their Application In Solar Cells

Since the 20 th century,the reserves of non-renewable energy such as oil and coal,have been greatly reduced with the increasing of modernization of industry.Energy crisis has been a global puzzle.On the other hand,the environmental pollution problems become serious with the rapid consumption of traditional fossil energy.Therefore,it is extremely urgent to develop a new renewable energy which should be environmentally friendly to meet human needs.Among them,solar energy resources have become one of the most promising energy sources because it shows wide distribution,safe and less pollution to the environment.Solar cell is an important way to use solar energy resources.The preparation method has been widely studied by researchers all over the world.At present,quantum dots-sensitized solar cells and perovskite solar cells are the most widely studied ones.Nanostructured materials are widely used by scientific researchers in these two types of solar cells,because they have excellent performance.For more than a decade,researchers have successfully synthesized one-dimensional?1D?and two-dimensional?2D?nanostructured materials,such as nanorods,nanowires,nanosheets and so on.There nanomaterials have attracted great attentions due to their high crystallinity and clear chemical composition in recent years.Among these 2D nanostructured materials,PbI₂ nanosheets and PbS nanosheets have been widely studied by researchers.This thesis includes two contents in total.The first is the preparation of PbI₂ nanosheets and their applications in perovskite solar cells,and the second is the preparation of PbS nanosheets and their applications in quantum dots-sensitized solar cells.In the first study,the uniform and dense PbO₂ film was prepared by electrochemical deposition,and then treated with HI ethanol solution to obtain PbI₂ films.The existence of PbI₂ was proved by XRD characterization.The SEM proves that the size,thickness and morphology of PbI₂ nanosheets can be adjusted by changing the parameter of electrodeposition current,and concentration of different HI acid ethanol solution.The generated PbI₂ nanosheets are almost all regularly inserted perpendicular to the FTO surface.The size of the nanosheets is about 500 nm,the distribution is relatively uniform,and the thickness is significantly increased.Finally,the experimental process of immersing CsBr methanol solution was changed to spin coating process.The PbI₂ film was spin coated with CsBr methanol mixed solution with the addition of DMF.The SEM proved that the addition of DMF promoted the formation of better perovskite films with the continuous optimization of the experimental process.The formed perovskite CsPbI_2-xBr_1+x film was more compact and the size of the perovskite grains became larger than that prepared without DMF.The assembled all-inorganic perovskite CsPbI_2-xBr_1+x solar cells were tested by IV and IPCE testing system.As a result,the short circuit photocurrent and open circuit photovoltage had been significantly improved.The power conversion efficiency was optimized to be 6.87% with 4-times spin-coating of CsBr methanol mixed solution.The photoelectric characters of cells were 1.03 V and 16.5 mA cm^-2.The fill factor was 40.4%.In this experiment,all-inorganic CsPbI_2-xBr_1+x perovskite solar cells were prepared for the first time based on electrodeposited PbO₂ film.This experiments provided a possible method for the preparation of large-area all-inorganic PSCs.In the second study,PbS nanosheets and PbS quantum dots were co-deposited on carbon nanotube?CNTs?films through SILAR method.SEM illustrates that regular PbS nanosheets were formed on carbon nanotube films.It also can be seen that the size,thickness and morphology of PbS nanosheets could be efficiently regulated by the proportion of CNTs to binder,the parameters of SILAR processes,and the p H of acidified CNTs.The generated PbS nanosheets have regular shape and uniform distribution.The EIS,Tafel curves and PCE test were performed in the CdS-CdSe quantum dots-sensitized solar cells,using PbS nanosheets-QDs co-modified CNTs films as the counter electrode.The results show that the formation of PbS nanosheets improve the electrocatalytic activity of the counter electrode and reduce the electron transfer resistance of the counter electrode/electrolyte interface.When the p H of acidified CNTs is 5,the open circuit photovoltage of the assembled solar cells is 0.55 V,the short circuit photocurrent is 12.84 mA cm^-2,and the fill factor is 59.9%.The power conversion efficiency is 4.25% which is nearly 60% higher than that of the lead-based PbS counter electrode.