Organic And Inorganic Hybrid Perovskite Materials And Optoelectronics Application

Organic-inorganic hybrid perovskite materials have the advantages of simple synthesis,rich chemical composition,excellent light absorption performance,and outstanding luminescence characteristics.In recent years,they have received extensive attention both in solar cells and light-emitting diodes.The performance of single junction solar cells based on perovskite materials is comparable to that of crystalline silicon cells,with the highest efficiency exceeding 25%.The electroluminance efficiency of near infrared light and green light based on perovskite materials has also exceeded 20%.The simple synthesis combined with the advantages of chemical composition diversity allows us to design and improve materials purposely addressing the problems we are facing or to meet the performance required by the device.This thesis aims at the design,synthesis,and application of perovskite materials,focusing on the preparation of perovskite materials that meet the needs of devices.The main results are as follows.Firstly,through studying the perovskite formation over different Pb I₂ precursors,crystallization kinetics and film qualities,carrier lifetimes,defects etc.,we reveal that the presence of solvent molecule as ligands in lead halide precursors,like DMF and DMSO.The interaction strength between Pb I₂ and ligands is effective to promote the conversion of precursors to perovskite for high-quality crystalline film formation.Pb I₂（DMF）with the weak coordinating ligand（DMF）allow being quickly converted into MAPb I₃ perovskite even at room temperature,whereas strong ligand DMSO constituted Pb I₂（DMSO）requires a thermal annealing to facilitate the conversion process.These indeed provide means to further control the crystallization kinetics of perovskite film.The resultant MAPb I₃ film made from Pb I₂（DMSO）precursor showed densely packed large grains,of which the grain boundaries are vertically aligned,leading to a much reduced film defects and longer carrier lifetime than those from Pb I₂（DMF）and pristine Pb I₂.As a result,highly efficient planar PVSCs with a PCE up to 17.0%have been achieved from Pb I₂（DMSO）precursor.Secondly,addressing the wide bandgap and poor charge transport issues of 2D perovskite,we synthesized novel lead-based 2D perovskites with mixed BA and FA cations,i.e.BA₂FA_n-1Pb_nI_3n+1.Compared to previously reported BA₂MA_n-1Pb_nI_3n+1,we found that replacing MA with FA can effectively lower the bandgap of the 2D perovskites.In particular,the BA₂FA₂Pb₃I₁₀ film showed a small bandgap of 1.51 e V,which is comparable to that of FAPb I₃（1.47 e V）.Moreover,we achieved a controlled alignment of the 2D perovskites by developing a novel one-step thiourea（THA）-assisted deposition method.With the improved bandgap and charge transport properties,inverted PVSCs with a planar structure of ITO/PEDOT:PSS/BA₂FA₂Pb₃I₁₀/PCBM/BCP/Ag achieved the best PCE of 6.88%,which is among the highest PCEs reported for FA based 2D perovskite solar cells at that time.The unencapsulated device retained 80%efficiency after storing in air for 25 days,indicating good stability against moisture and oxygen.Finally,in order to achieve efficient perovskite light emitting diodes,we fabricate2D/3D mixed perovskite films by introducing large-cation ligands,that is,butylammonium bromide（BABr）into FAPb Br₃ via a two-step interdiffusion method.FAPb Br₃ is chosen for its better thermal stability over MA-based perovskites.Using this as a model system,we investigate in details the effects of incorporating large-cation ligands on the composition,morphology,optoelectronic properties of the resulting perovskite films,as well as on the performance of the Pe LEDs based on the corresponding perovskite films.Compared to a pristine FAPb Br₃,the formation of mixed 2D/3D perovskite films significantly enhances the device performance in both efficiency and operational stability.The best performing device using a mixed 2D/3D film made with BABr shows a maximum EQE of 7.46%at 147.7 m A cm^-2,and a luminance of 37 720 Cd m^-2 at 5 V.Our study demonstrated that the 2D/3D perovskite fabricated by two-step method is capable for high performance Pe LEDs,with further optimization a higher efficient 2D/3D Pe LEDs is available.