Influence Of Molecular Steric Hindrance Effect On All-inorganic Perovskite Films And Solar Cells

In recent years,perovskite halides have become the focus of development and research due to their excellent photoelectric properties.Among them,metal halide all-inorganic perovskite（Cs Pb X₃;X stands for halogen）solar cells arouses great interest due to their excellent thermal And light stability.However,its complicated phase transition mechanism and difficult-to-control crystallization process have not been well explained.This thesis elaborates on three aspects.The first part is the basic theoretical,which introduces in detail the preparation methods and advantages and disadvantages of perovskite solar cell films,and provides a complete description of the theory of preparing perovskite crystals by solution method.The theory includes classical nucleation theory,classical growth theory,Lamer mechanism,Oswald maturation model,while considering the crystallization based on the substrate,its crystallization theory-island,the layered growth process is still applied.Then it is a high-level overview of the crystalline phase transition path.At first,it is an orthorhombic perovskite crystal.This phase has environmental temperature and humidity stability,but it is not a photosensitive phase and does not have the possibility of preparing solar cells.As temperature increases,The phase has transformed into the tetragonal phase and cubic phase,both of which have a good photosensitizing effect.Thorough research on crystallization theory is of great help to the introduction of steric hindrance in the right time and the right method to control crystallization.Finally,the significance of steric hindrance is introduced in detail,and its huge potential in the field of perovskite film crystallization,which has not been exploited,combined with various theories of solution crystallization,to speculate on the influence of steric hindrance,and seek A more appropriate control method.The second part is material preparation.Based on the previous crystal adjustment methods,this work chooses the second type to introduce additives to achieve the purpose of adjusting the perovskite film crystals.Analysis of the crystallization process found that if the alkyl chain length on the cycloalkane carboxylate is increased,it is possible to improve the final crystalline form of the perovskite film,and even affect the phase transition during the annealing process,thereby improving the stability and stability of the perovskite crystal.Photoelectric performance.We used the solution method to crystallize and prepared the crystals of different cycloalkane carboxylate additives.Through the morphology test,we found the conditions under the best crystallization state.Through the determination of the crystallization rate,we tried to give a simple mechanism.Compare the X-ray powder diffraction（XRD）test during the film annealing process and draw corresponding conclusions.Combined with the Fullprof crystallization test chart and simulation calculation,and inverted the valence bond theory,a new intermediate product—monoclinic phase all-inorganic perovskite film was finally obtained.On this basis,it was confirmed that the impedance effect due to cycloalkane crystallization The existence of,postponed the whole process of perovskite crystallization.In addition,we have obtained the film additive conditions that are stable to the external environment,which proves that the additive does not sublime with the annealing process,but appears on the crystal surface in a passivated form after the reaction is completed.This is the key reason for the stability of the film.The third part is the device performance test.Based on the good crystallization properties of the previously prepared crystals,we compared the photoelectric properties of the additive films,and measured the relative strength and defect state density of excitons.They undoubtedly have excellent characteristics,that is,when the additive ring increases,The photoelectric properties of the film will first increase and then decrease,which corresponds to the inherent characteristics of the film.Finally,the best quality thin film conditions were applied in the solar cell device（cesium cyclohexanecarboxylate as an additive）,the open circuit voltage was 1.26V,the short circuit current was 15.51 m A/cm²,the fill factor exceeded 79%,and the photoelectric conversion efficiency（PCE）reached 15.5%.It provides useful help for further research on the crystallization behavior of all-inorganic perovskite and its solar cell devices.