Preparation Of High Quality CsPbI₃ Inorganic Perovskite Films By Additive Engineering And Its Application In Solar Cells

In recent years,perovskite materials have attracted the attention and favor of researchers due to many advantages such as high optical absorption coefficient,adjustable band gap,and long carrier diffusion distance,and become a research hotspot in the field of photovoltaic.Perovskite solar cells（PSCs）have developed rapidly in more than a decade.The photoelectric conversion efficiency（PCE）has increased from 3.8%in 2009to 25.7%today,showing great commercial application potential.However,there are still some technical challenges in the commercialization of perovskite solar cells.Among them,organic components in organic-inorganic hybrid perovskites have problems such as volatile and poor thermal stability,which can easily lead to the destruction of perovskite crystal structure and weaken the photoelectric performance of battery devices.All-inorganic perovskite materials（Cs Pb X₃,X=Cl,Br,I）are highly sought after by researchers due to the absence of organic components and greatly improved thermal stability.Among them,Cs Pb I₃ perovskite has been consistently recognized as one of the most competitive photovoltaic materials due to its ultra-high melting point and suitable band gap（～1.7 e V）.However,Cs Pb I₃ perovskite still has problems such as poor film quality and easy phase transition,and there is still much room for improvement in the efficiency of battery devices.The key to improve the photoelectric conversion efficiency of battery devices is to improve the quality of perovskite films.High-quality perovskite films can not only improve the absorption ability of photons,but also promote the extraction and transmission of electrons and holes by the charge transport layer.In addition,the group assignment ratio of the perovskite precursor plays a crucial role in the quality of the film,and precise regulation of its components is expected to obtain high-quality perovskite films.In this paper,the quality of Cs Pb I₃ perovskite films was improved by additive engineering to prepare efficient and stable Cs Pb I₃ all-inorganic perovskite solar cells.The main research content is as follows:（1）Imidazole was added into the precursor solution of perovskite as an additive to prepare high-quality Cs Pb I₃ perovskite films with large grains and low density of defect states.The results show that imidazole,as a kind of amphoteric additive,has both Lewis acid and base properties,which can not only regulate the crystallization dynamics of perovskite,delay the crystallization rate of perovskite,but also synergize with passivating charged defects(uncoordinated Pb²⁺and I^-)in the thin film,effectively reduce the density of defect states,inhibit the non-radiative recombination of charge carriers,and prolong the carrier lifetime.Amphoteric imidazole induced the formation of thin films with large grains and low defect density,which significantly improved the quality of perovskite films.The photoelectric conversion efficiency of the prepared cell device was 14.88%,and the initial efficiency was 83.1%after 500 h storage in the air environment.（2）In order to reduce the invasion of water vapor into Cs Pb I₃ perovskite and improve the hydrophobicity of the film,TMAI with long-chain organic cations was used as the additive of the perovskite layer.The results show that TMA⁺not only enhances the moisture resistance of the films,but also passivates Cs vacancies as well as uncoordinated I^-in the films and inhibits non-radiative recombination.TMAI effectively improved the quality of the Cs Pb I₃ all-inorganic perovskite film and improved the photoelectric performance of the battery device.The efficiency of the final prepared battery device reached 14.44%,and the long-term stability of the device was significantly improved.（3）The homologous component Pb I₂ was introduced into the perovskite precursor solution as an additive to realize the regulation of precursor components,and to explore the effects of different amounts of Pb I₂ on perovskite film defects and device performance.The results show that an appropriate amount（1.0 mol%）of Pb I₂ in the Cs Pb I₃ all-inorganic perovskite film can passivate the defects at the grain boundaries of the film,inhibit the non-radiative recombination of charge carriers,prolong the fluorescence lifetime of charge carriers,and finally improve the quality of the perovskite film.The photoelectric conversion efficiency of the cell device is 14.39%.