Efficient And Stable Inorganic Perovskite Solar Cells Via Solution And Vapor Deposition Processing

In recent years,all-inorganic perovskite CsPbI₃ has attracted the most attention in the photovoltaic field due to its excellent light stability,thermal stability and suitable band gap.However,CsPbI₃ tend to transfer into a more thermodynamically stable yellow phase at room temperature because of the small radius of Cs⁺induced inappropriate tolerance factor,and lose its photovoltaic properties.In this regard,obtaining and maintaining stable black phases of CsPbI₃ at room temperature is the key to realize high-performance inorganic perovskite solar cells（PSCs）.Driven by inventions of numerous processing methods for preparing high-quality CsPbI₃ perovskite thin films,the power conversion efficiency（PCE）of CsPbI₃ PSCs has quickly ramped over 20%within only six years.Interestingly,the crystal structure,photoelectric properties and phase stability of CsPbI₃perovskite thin films are highly dependent on the selection of preparation methods.Therefore,it is of vital importance to study the underlying relationship between processing methods and photoelectric properties of corresponding perovskite films and this will promote the development of inorganic PSCs.In view of this,processing methods of inorganic CsPbI₃ perovskite were studied in detail.Efficient and stable CsPbI₃photovoltaic devices were realized by solution deposition and vapor deposition.The main contents are as follows:A solution method for depositing efficient and stable inorganic CsPbI₃ PSCs was developed.The bulk and surface electronic states of CsPbI₃ films were modified by using Cs Pb Br₃ perovskite nanocrystals which were covered by a new type of short chain ligands—naphthenate acid,and the charge transfer property was consequently enhanced.The results demonstrated that the modification of nanocrystals have the effect of elemental doping as well as of molecular surface functionalization.The optimized devices exhibited a better energy-level alignment and outstanding charge extraction capacity at perovskite/hole transport layer interface,which resulted in a dramatic improvement on open circuit voltage,short-circuit current density,and fill factor,yielding a power conversion efficiency（PCE）of 17.4%with enhanced humidity stability.A vapor deposition method was proposed to fabricate efficient and stable inorganic CsPbI₃ PSCs.A PCE over 16%was realized by combining high-throughput experimentation and atmosphere-controlled annealing（ACA）process.The deposited films present lateral gradient in composition which allowed us to systematically investigate the effect of stoichiometric ratio between Cs I and Pb I₂ on photovoltaic properties.Excessive Cs I was found to reduce grain size and promote the formation of Cs₄Pb I₆ structure at grain boundaries and this secondary structure suppressed phase transition and improved the long-term stability of CsPbI₃ films.ACA process can effectively reduce the defect state density in CsPbI₃ films,which suppressed non-radiation recombination and improved the performance of the devices.In addition,efficient devices can be obtained under a wide composition window based on ACA process.The champion device delivered a PCE of 16.3%,which is the highest value among up-to-date reported ones of vapor-deposited all-inorganic PSCs.In summary,this thesis systematically studied the internal relationship between processing methods（both solution deposition and vapour deposition）and the basic properties of CsPbI₃ films.In order to achieve stable and efficient inorganic CsPbI₃ PSCs,appropriate strategies were adopted to optimize the photoelectric properties of CsPbI₃films and consequently improve the device performance.This thesis may help the further development of all-inorganic PSCs.