Preparation Of High-quality CsPbI₃ Thin Films And Their Device Performance Optimization

Organic-inorganic hybrid perovskite solar cells have demonstrated excellent photovoltaic potential due to the photoelectric conversion efficiency from 3.8%at the first time to the current champion efficiency of 25.7%.Although the efficiency is high,the volatile organic molecules affect its stability and hinder the commercial application.The CsPbI₃ perovskite solar cells formed by using Cs⁺to replace organic molecules have relatively good thermal stability.However,there are still some problems in CsPbI₃perovskite solar cells,including a gap between the current maximum efficiency and the theoretical efficiency,many interface complexes and easily phase transition.Therefore,it is necessary to prepare CsPbI₃ perovskite films with high quality and good thermodynamic stability.In this paper,the effects of DMAI under excess HI on the morphology and device performance of?-CsPbI₃,the internal and external factors of the phase transition of all-inorganic CsPbI₃ films,and the CsPbI₃ perovskite solar cells based on the Dion-Jacobson type 2D-3D structure are discussed.The specific works are as follows:1.The synthesized DMAI powder with different proportions are added to the perovskite precursor solution,making the DMA⁺and Pb I₂ form a Lewis adduct,which slows down the crystallization rate,improves the film quality,and reduces surface defects.I^-in DMAI formed under excessive HI can fill I vacancies in the crystal structure,reducing lattice defects,increasing the repeatability and efficiency of the device,and improving the device efficiency up to 18.45%.2.High-quality CsPbI₃ thin films were prepared by solution spin coating and thermal evaporation,and the inducing factors of the phase structure instability of CsPbI₃were explored.The factors for its phase transition are Gibbs free energy(internal factor)and polar solvent(external factor).Both of these are closely related to the size of the grain size.When the grain size of the film is larger,the vibrational entropy increases and its own stability is lower.On the contrary,the smaller the grain size of the film,the more grain boundaries will be increased,and the more likely the polar solvent contained in the charge transport layer will induce the phase transition of the light absorption layer film.3.Post-processing the 3D perovskite film using a solution containing a divalent spacer molecule 2,2?-(ethylenedioxy)bisethylamine hydrochloride(EDBECl₂)to form a DJ-type 2D-3D perovskite film structure,which could be maintained for more than one week in atmospheric environment.The device efficiency of the film after treatment reaches 17.23%.