Preparation Of CH₃NH₃PbI₃ Perovskite Thin Films At Low Temperature And Their Application In Solar Cells

In recent years,the CH₃NH₃PbI₃ perovskite thin films have a series of advantages,such as suitable bandgap width?1.5eV?,high absorption coefficient,high carrier lifetime and mobility,so they have become a research hotspot in the field of photovoltaics.At present,the highest photoelectric conversion efficiency of perovskite solar cells have reached 22.7%,comparable to that of crystalline silicon solar cells.During the experiment,the perovskite absorber layer was mainly prepared by one-step or two-step spin coating.The spin coating method has the advantages of simple equipment,convenient operation,etc.,but the spin coated film generally needs to be annealed at 100°C,which is not suitable for the flexible substrate.In addition,the uniformity of the film is significantly reduced with the increase of the spin coating area,thereby the conversion efficiency of the cells has been affected serious.In this dissertation,the low-temperature,large-area preparation of CH₃NH₃PbI₃ thin films was investigated,and a planar perovskite solar cell with n-i-p structure was constructed.The main research contents and results are as follows:?1?PbI₂ films react with methylamine?MA⁰?gas to produce CH₃NH₃Pb I₃ films.In the experiment,PbI₂ films were prepared by spin coating method.MA⁰ gas has been achieved from its ethanol solution by volatilized.The highest reaction temperature was 70°C.The results showed that the color of the films prepared by the reaction of PbI₂ with MA⁰ was yellow-brown,and this structure were perovskite measured by XRD,but their stability were poor.When they were applied as the absorber layer of n-i-p solar cell,the efficiency was only 2.38%.Adding a certain amount of HI solution in the PbI₂ precursor can improve the stability of the films and increase the cell efficiency to 5.68%.?2?HPbI₃ films react with MA⁰ to prepare CH₃NH₃PbI₃ films.First,the HPbI₃powder was prepared by PbI2 reacting with HI,then the HPbI3 solution was prepared,and spin-coated it into the HPbI₃ films.Finally,the perovskite films were formed by HPbI₃ reacting HPbI₃ films with MA⁰ gas.The highest temperature of the entire preparation process was 70°C.The results showed that the volume of MA⁰ solution had a great influence on the morphology of CH₃NH₃PbI₃ thin films and the performance of the solar cells.When the volume of MA⁰ solution was 200?L,the surface coverage of the CH₃NH₃PbI₃ films were high and dense,and the efficiency of solar cells was 15.11%.The preheating temperature of the HPbI₃ precursor has an important influence on the quality of the perovskite films.When the preheating temperature is 20-30°C,the particles of the prepared films are larger and tightly bounded.As the preheating temperature increases,the films particle size decreases and the number of holes increases,and the performance of the solar cells decreases.?3?Preparation of CH₃NH₃PbI₃ thin films by gas-phase assisted electrochemical deposition.First,the PbO₂ thin films were prepared by electrochemical deposition method,and then reacted with HI gas to obtain the PbI₂ thin films.Next,the obtained PbI₂ reacted with HI and CH₃NH₂ mixed gas to form CH₃NH₃PbI₃ films.The highest temperature of the entire preparation process was 100°C.The experimental results show that:1)Electrodeposition voltage has an important influence on the surface morphology and microstructure of PbO₂ films;2)During the conversion of PbO₂ to PbI₂,the crystallinity of PbI₂ gradually increases with the decrease of reaction time.The best reaction time is 10 min.3)In the conversion process of perovskite,a uniform and dense perovskite films can be obtained when the volume ratio of HI/CH₃NH₂ solution is 1:2.