Metal Ion Incorporating Inorganic Halide Perovskite And Their Application In Light Emitting Diode

This thesis mainly investigates the optoelectronic performance of cesium(Cs)based inorganic halide perovskite(CsPbBr3)and its application in light-emitting diodes(LED)In recent years,Cs based inorganic perovskite has been widely investigated in highly efficient and stable perovskite LED,due to its superior strengths such as excellent luminous performance and better stability compared with organic perovskite materials.Especially rapid progress has been made in green and blue emitting materials based on CsPbBr3,which results in efficient and stable perovskite LED devices.Among this,the stability of green LED still remains as a vital issue though its efficiency has already reached the commercial standard.Therefore,we developed all-inorganic perovskite materials by incorporating alkali metal ion with small ionic radius,and the efficiency and stability of perovskite LED devices is greatly improved.We analyzed its passivation mechanism by ultroviolet photoelectron spectrometer(UPS),X-ray photoelectron spectroscopy(XPS)and X-ray diffraction(XRD).Moreover,the main issues limiting CsPbBr3 based emitting materials are the low efficiency and poor spectral stability of blue LED.Based on these issues,and inspired by the metal ion incorporating methods,we successfully tune the bandgap of perovskite materials by simply incorporating different alkaline-earth metal ions into CsPbBr3 materials,resulting in the achievement of different perovskite emission peaks.At the meanwhile,we confirmed that these alkaline-earth metal ions have been successfully occupied the perovskite lattice according to XRD and physical simulation.Besides,we also characterized the optoelectronic performance and film quality of alkaline-earth perovskite films by ultraviolet-visible(UV-vis)absorption spectrum,photoluminescence spectrum(PL)and scanning electron microscopy(SEM).Furthermore,blue LED,based on alkaline-earth metal ion incorporating perovskite,show significantly improved spectral stability.The main content of this thesis is shown as followed:1.Perovskite LED devices with the incorporation of organic ligands generally displays poor thermal stability and working stability,and it is likely correlated with the weak heat resistance and other drawbacks of organic ligands.Therefore,all-inorganic perovskite materials make it possible to achieve stable perovskite LED devices.We dramatically enhanced the device stability by incorporating alkali metal ion with small ionic radius lithium(Li+).The Li+incorporation in perovskite greatly passivates the defects in perovskite materials.The LED devices based on this method show optimized external quantum efficiency(EQE)of 16.2%,and could maintain excellent working stability at a high brightness of 10,000 cd/m2.We analyzed the effects of incorporating Li+by conducting tests such as UPS,XPS,XRD and so on,and realized that it could not occupy the perovskite lattice.It is because the incorporation of LiBr leads to a Br-rich environment that could result in the passivation of defects in perovskite materials.2.Inspired by the metal ion incorporating methods above,alkaline-earth metal ion strontium(Sr2+)was incorporated into CsPbBr3 based perovskite materials to investigate effecting bandgap structure.We noticed that the emission peak of CsPbBr3 shifts gradually toward to blue side with the incorporation of different ratios of Sr2+.However,there is obvious shift on the emission spectrum of Sr2+ incorporating perovskite film when under conditions like thermal heating due to the weaker structure stability of Sr2+incorporating perovskite compared to CsPbBr3 itself.Therefore,we further introduced small amount of organic ligand phenylethylamine(PEA)into the system,and found that the films based on this kind of perovskite displayed improved spectral stability under thermal heating,UV light illumination and some other conditions by tests of PL,UV-vis absorption spectrum and so on.Besides,perovskite LED devices based on our perovskite show superior spectral stability under constant current.The device with 20%Sr2+incorporation,whose emission peak locates at 491 nm,show EQE of 4.1%.Our study solves the extensive issue on poor spectral stability of blue emitting perovskite materials.3.Based on the aforementioned results,we further investigated the effects of different alkaline-earth metal ion incorporation,and effectively tuned the bandgap of CsPbBr3 based perovskite material.Perovskite materials with different emission peaks are achieved.CsPbBr3 perovskite,whose emission peak locates on green emission range(524 nm),has already been widely applied in perovskite LED due to the excellent luminous performance.Currently,the methods to tune bandgap structure are mainly limited by incorporating different halide ions or forming low dimensional perovskite structure by introducing organic ligand into the system.We effectively tuned the bandgap of perovskite materials by incorporating different alkaline-earth metal ions,resulting in different levels of blue shift on CsPbBr3 based perovskite emission peaks.We explored different alkaline-earth metal ion incorporation in CsPbBr3 to affect its optoelectrical characters.