Study On Improving The Photovoltaic Performance And Stability Of All-inorganic CsPbI₂Br Perovskite Solar Cells

Perovskite materials have attracted much attention due to their high optical absorption coefficient,long carrier mobility and low-cost preparation methods.Inorganic CsPbI₂Br perovskite also has the advantages of appropriate band gap and strong photothermal stability.In recent years,more and more researchers began to focus on the solar cell research of this system,and the photoelectric conversion efficiency（PCE）of CsPbI₂Br perovskite solar cells has made a great improvement in just a few years.However,there is difference between the reported efficiency and its theoretical limit value.This is because the perovskite films are usually accompanied by a large number of internal defects and surface defects,leading to carrier recombination.In addition,the energy level mismatch between the optical absorption layer and the charge transfer layer is also one of the reasons for carrier loss.The long-term stability of devices is also a very important point in the research of perovskite solar cells.Based on the above problems,this paper mainly takes focus on CsPbI₂Br perovskite films to improve the photoelectric performance and stability of CsPbI₂Br perovskite solar cells through additive engineering and interface defect passivation.The specific research contents are as follows:（1）Nitrogen-doped graphene quantum dots（N-GQDs）were added to CsPbI₂Br perovskite films.Due to a large number of organic functional groups,N-GQDs can interact with the uncoordinated Pb²⁺and I^-/Br^-in perovskite,achieving the function of passivating the grain boundary and surface defects of the light absorption layer,and finally obtaining CsPbI₂Br perovskite film with flat morphology and low defect density.At the same time,N-GQDs with good conductivity play the role of electronic bridge in the grain boundary,which can help the photogenerated electrons to transfer smoothly to the electron transport layer,reducing the recombination at the grain boundary,and the devices with N-GQDs achieve 14.39%PCE.（2）N-GQDs and NaCl were added to the perovskite layer at the same time.Because of similar physical and chemical properties,Cl will partially replace the position of Br after entering the perovskite structure.Cl-doping aligns the energy level of CsPbI₂Br,decreasing the energy barrier between perovskite and P3HT,so that the photogenerated hole can reach the hole transport layer only by overcoming the lower energy barrier.N-GQDs and NaCl can synergistically promote the transport and extraction of carriers in CsPbI₂Br perovskite solar cells.And finally the devices with binary additives achieved 15.37%PCE.（3）A ultra-thin polymethylmethacrylate（PMMA）layer is covered on the CsPbI₂Br pervoskite layer.The long chain of PMMA polymer has many functional groups,which can passivate the defects on the perovskite surface,promoting the power conversion efficiency of CsPbI₂Br perovskite solar cells.On the other hand,the vitrified PMMA has strong hydrophobicity,which can insulate the water molecules in the air from the erosion of the light absorption layer and increase the humidity stability of the material.At the same time,PMMA can also reduce diffusion of I ions in perovskite and Ag electrode,avoiding the generation of Ag I.