Investigations Of Synthesis And Stability About All-Inorganic Cesium Lead Halide Perovskite Nanomaterials

Perovskite nanomaterials have been attracted great attention in the fields of display and light-emitting diodes（LED）due to high photoluminescence quantum yields（PLQYs）,high color purity,narrow band-width,and a widely tunable emission spectrum from ultraviolet to visible.However,their stabilities are highly sensitive to temperature,water,light,and heat,and are prone to decompose,which is one of the major barriers for practical applications.Therefore,it`s very crucial to improve the stability of the perovskites for future applications.In this thesis,we focus on the stability of perovskite nanomaterials.Starting from its growth mechanism,we put forward a low temperature two-step process and doping process to obtain zero-dimensional,one-dimensional and two-dimensional perovskite structure,and explore its stability mechanism.The research results are as follows:（1）Direct synthesis of perovskite phase CsPbI₃ nanowires via two-step injection at low temperatureIn this work,regarding that the CsPbI₃ is unstable and can be easily transformed from the perovskite phase into the orthorhombic（δ）CsPbI₃ with an undesired wider band gap（2.82 e V）,we report a simple approach to directly grow highly stabilized perovskite phase CsPbI₃ nanowires via low temperature two-step injection method.We systemically investigate the effect of reaction temperature on crystallization,morphologies,structures,and optical properties of CsPbI₃ nanowires.We find that low reaction temperature,capping ligand protection,and a second growth opportunity are key to the successful growth of perovskite phase CsPbI₃ nanowires.The X-ray diffraction（XRD）,photoluminescence（PL）,and UV-vis absorption results verify that these perovskite phase nanowires maintain excellent stability at room temperature for 90 days in an inert atmosphere.The excellent optical properties and narrow band gap of the phase stable CsPbI₃ nanowires offer great potential in the field of optoelectronic devices.（2）Enhancing stability of CsPbI₃ perovskite nanocrystals through copper substitutionIn this work,due to the fact that perovskite phase CsPbI₃ is unstable,we report a low-temperature and atmospheric approach to synthesize Cu²⁺-doped CsPbI₃ nanocrystals with enhanced stability.Results show that the stability of solution and film both have been improved after Cu²⁺doping.In particular,the Cu²⁺-doped CsPbI₃ film can maintain red luminescence for 35 days in air while the undoped ones transformed into the nonluminescent yellow phase in several days.Furthermore,first-principles calculations verify that the enhanced stability is ascribed to the increased formation energy due to the successful doping of Cu²⁺in CsPbI₃.The formation energy of undoped CsPbI₃ is-14.0965 e V,while the formation energy of 3.125%Cu²⁺doped CsPbI₃ is-14.2609 e V.Benefiting from such an effective doping strategy,the as-prepared Cu²⁺-doped CsPbI₃ as an emitting layer shows much better performance compared with that of the undoped counterpart.The turn-on voltage of the Cu²⁺-doped quantum-dot light-emitting diode（QLED）（1.6 V）is significantly reduced compared with that of the pristine QLED（3.8 V）.In addition,the luminance of the Cu²⁺-doped QLED can reach 1270 cd/m²,which is more than twice that of the pristine CsPbI₃QLED（542 cd/m²）.The device performance is believed to be further improved by optimizing the purification process and device structure,shedding light on future applications.（3）Synthesis and improve the stability of CsPbCl₃ nanoplatelets via Mn²⁺dopingIn this work,considering that the two-dimensional CsPbCl₃ nanoplatelets have low PLQYs and poor stability,we report a low-temperature and atmospheric approach to synthesize highly luminescent Mn-doped CsPbCl₃ nanoplatelets.Results show that the moderate temperature,approximate growth time,and appropriate Mn-Pb feed ratio are the key to the successful growth of Mn-doped CsPbCl₃ nanoplatelets with high PLQYs.The nanoplatelets exhibit excellent stability at room temperature in air（over 60 days）.Apart from the enhanced stability,the PLQY of our Mn-doped CsPbCl₃ nanoplatelets is also enhanced,up to 53.76%,which is the highest reported value in Mn-doped two dimensional all-inorganic halide perovskites.Due to the enhanved stability and high PLQYs,for the first time,both orange-red and warm white light-emitting diodes（LEDs）have been achieved through the nanoplatelets as the color conversion materials.Moreover,flexible composite fluorescent polymer films based on the nanoplatelets are demonstrated with high luminescence and stability（over 6 months）,which indicate prominent potential in flexible displays.