The Investigation Of Thin Film Optimization And Performance Improvement Of All-inorganic CsPbX₃ Perovskite

As one of the representatives of the third-generation photovoltaic technology,perovskite solar cells（PSCs）stand out due to their excellent photoelectric properties,simple preparation methods,and low production costs.The power conversion efficiencies（PCEs）of the devices have jumped from 3.8%（2009）to 25.7%（2022）,with broad application prospects and huge development potential.Wide-bandgap all-inorganic solar cells have great advantages as sub-cells of tandem devices.During the commercialization of perovskite solar cells,the PCEs and stability of the devices are very important.This dissertation is mainly aimed at this key problem of wide-bandgap all-inorganic Cs Pb X₃ perovskite solar cells.By introducing technical means such as interface buffer layer,interface passivation,surface reconstruction and surface doping,the morphology optimization of perovskite thin films,defect passivation,lattice match at the interface,energy level adjustment and efficient carrier transport are regulated.The internal mechanisms of the relevant effects are systematically studied and verified via the combination of experiments and theoretical calculations.Finally,the purpose of improving the performance and stability of the devices is realized.The main research results of this dissertation are as follows:（1）Research on perovskite film and interface modification based on the introduction of Cs Br buffer layer.In this study,improvements in the Cs Pb I₂Br perovskite film and interface-related properties were achieved by introducing a Cs Br interfacial buffer layer between the electron transport layer/perovskite layer.The results show that the introduction of Cs Br effectively reduces the surface roughness of the electron transport layer,optimizes the growth of the perovskite film,and improves the crystalline quality and light absorption of the perovskite film.Besides,it alleviates the lattice mismatch at the interface and reduces surface energy and surface deformation of the perovskite.Hence,the stability of the surface structure is enhanced.Furthermore,the PCE of the device is improved and the film and device stability under various aging conditions such as continuous illumination,continuous heating,high humidity environment and long-term storage are greatly enhanced.（2）Research on improving the optoelectronic performance and stability of Cs Pb I₂Br-based perovskite solar cells based on synergistic passivation of organic molecules of large size and inorganic ions.In this study,in view of the problem that the large-size organic molecular passivation cannot take into account the surface and bulk defects simultaneously,it is found that the effect of mixed passivation is better than that of single one by using PEABr organic molecules and Cs Br inorganic ions for synergistic passivation.The relevant characterizations reveal that PEA⁺is mainly located on the surface of the perovskite film to passivate the defects at the grain boundaries in the form of two-dimensional perovskite,while Cs⁺and Br^-can penetrate deep into the perovskite and reduce ionic defects.Multiple passivation effects from top to bottom are achieved in the perovskite film.The mixed passivation tunes and optimizes the energy band alignment,which enhances carrier transport and suppresses nonradiative recombination.In addition,it also reduces distortion of the cells and improves film quality,which exhibits excellent moisture resistance and stability against continuous heating,continuous illumination,and long-term storage conditions.Finally,the Cs Pb I₂Br perovskite solar cells based on mixed passivation realize a high efficiency of16.70%,which is among the highest values in the same period.（3）Research on improving the optoelectronic performance and stability of all-inorganic Cs Pb IBr₂ perovskite solar cells based on surface reconstruction strategy.In view of the shortcomings of high perovskite surface defects and structural disorder,surface reconstruction treatment of perovskite films with organic molecule FAI significantly improves the film morphology,alleviates the disorder of the perovskite surface structure and reduces defects,obtaining a high-quality perovskite film without pinholes.The interaction between the organic groups and dangling bonds enhances the migration barrier,which is beneficial to the phase stability of the films.The surface reconstruction improves the energy band mismatch between the surface of the perovskite film and the hole transport layer,suppressing nonradiative recombination and improving the transport efficiency of carriers.The devices show good stability under aging conditions such as continuous heating,continuous illumination,and long-term storage.The surface reconstruction significantly reduces energy loss,achieving a high open circuit voltage of 1.34 V and the highest PCE of11.31%in the same period.Besides,the device also shows good responsivity,detectability and excellent cycle reliability as a photodetector.（4）Research on improving the optoelectronic performance and stability of all-inorganic Cs Pb IBr₂ perovskite solar cells based on the synergistic effects of surface p-type doping and passivation.In view of the problems that perovskite surface has high defects and poor conductivity,this study uses organic molecule DAPI₂ to realize p-type doping on the surface of perovskite film which can raise the surface energy level,optimize the energy band alignment,increase the built-in electric field,reduce the series resistance and transfer resistance,increase the recombination resistance,and improve and balance the mobility of electrons and holes,making the carrier transport process more efficient.The surface doping also improves the film morphology,increases the surface migration barrier and enhances the stability of the perovskite film.Finally,the reduced energy loss results in a high open circuit voltage of 1.33 V and a high PCE of 11.02%.The device exhibits excellent illumination and thermal stability in high-humidity environments,as well as excellent long-term stability in dry air.In addition,surface doping also achieves the effect of chemical encapsulation.After the device is immersed in water for more than 30 minutes,the leaked lead concentration is still within the safe range of human blood lead concentration,which is an excellent environment-friendly device.