Performance Tuning Of Pure Bromine-based All-inorganic Perovskite Light-emitting Diodes

Metal halide perovskites have emerged as a new generation of promising optoelectronic materials due to their unique optoelectronic properties and low-cost solution processing techniques,and are widely used in optoelectronic devices such as solar cells,lasers,and light-emitting diodes.Among them,perovskite light-emitting diodes（Pe LEDs）have many excellent properties,such as high fluorescence quantum yield,wide color gamut,and easy processing,and have great application potential in the field of next-generation lighting and display.At present,the external quantum efficiency（EQE）of green and red Pe LEDs has exceeded 23%,and the EQE of Pe LEDs with near-infrared（NIR）emission wavelengths has also exceeded 20%,showing good electroluminescence（EL）performance.However,the development of Pe LEDs is also subject to many limitations,including the roll-off of EQE at high current densities,short lifetime,low efficiency of blue light devices,and inability to obtain peak emission wavelengths larger than 800 nm due to bandgap limitations,etc.Among perovskite materials,pure bromine-based all-inorganic perovskite materials have better environmental stability,conductivity,and spectral stability,so light-emitting devices based on pure bromine-based all-inorganic perovskite materials can achieve higher Luminous brightness and working life.However,pure bromine-based all-inorganic Pe LEDs prepared by the solution method have problems such as poor film coverage,uncontrollable crystallization process,and low light-emitting device efficiency,so it is still challenging to realize efficient and stable pure bromine-based all-inorganic Pe LEDs.Moreover,with the improvement of living standards,people are increasingly calling for optoelectronic products that are flexible,smart wearable,and portable.Therefore,it is of great significance to study and prepare high-performance flexible Pe LEDs.In this paper,the photoelectric performance of pure bromide-based all-inorganic perovskite light-emitting diodes can be effectively adjusted by controlling the crystal size of perovskite,passivating defects,and designing and optimizing the electrode structure.The specific innovative achievements are as follows:（1）Pure bromine-based all-inorganic perovskite blue Pe LEDs based on NiO_x anode interface.Using NiO_x as the anode interface and adjusting the Cs/Pb ratio,blue Pe LEDs based on pure bromine-based all-inorganic perovskite were prepared for the first time by a solution method.The study found that during the crystallization process of perovskite,the NiO_x interface can effectively promote the formation of Cs₄Pb Br₆,thereby effectively restricting the growth of Cs Pb Br₃,thereby reducing the grain size,widening the perovskite bandgap,and finally achieving the maximum brightness.Sky blue Pe LEDs with 1610 cd/m² and the highest EQE of 1.58%.Our work will provide a useful exploration for the development of efficient and stable pure bromide-based all-inorganic perovskite blue Pe LEDs.（2）Preparation of pure bromine-based all-inorganic Pe LEDs by triblock copolymer-assisted film-forming method.Introducing polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer（PEO-PPO-PEO）into the pure inorganic perovskite Cs Pb Br₃ precursor solution effectively improved the perovskite light-emitting layer film morphology,accelerate perovskite crystallization,reduce the formation of grain boundaries,reduce the defect density and non-radiative recombination rate of perovskite films and grain boundaries,effectively improve the photoluminescence quantum yield（PLQY）of Cs Pb Br₃ films.The introduction of the triblock copolymer not only greatly shortens the annealing time of the perovskite film,but also greatly improves the EL performance of Pe LEDs.The maximum brightness,peak current efficiency and EQE of the device are 14700 cd/m²,30.7 cd/A and 10.5%.,respectively.（3）Perovskite materials are considered as potential materials suitable for flexible wearable displays due to their excellent optoelectronic properties and flexibility.However,the brittleness of conventional ITO electrode,time cost and the non-radiative recombination caused by the defects of perovskite films hinder their commercialization and application in flexible Pe LED.Herein,the WO₃/Au/WO₃ electrode replacing the widely used ITO electrode to reduce energy barrier between bottom electrode and PEDOT:PSS hole transport layer.It is conducive to hole injection.At the same time,P123 was introduced to optimize the crystallization kinetics and recombination kinetics.The nucleation and crystallization process ends in a very short time to obtain uniform distributed small-size grains.Moreover,the molecular additive containing C-O functional group is demonstrated to heal the non-radiative recombination centers by donating its lone pair electrons to the uncoordinated Pb²⁺.Furthermore,the interaction between P123 and perovskite enhances the flexibility of emissive layer.Consequently,we report the high-performing green Pe LED（514 nm）with the maximum EQE exceeding 14.45%and flexible Pe LED（516 nm）with the maximum EQE of 11.9%by relying on a synergetic modulation strategy.The flexible Pe LED shows the Luminance can keep 55.56%and the current efficiency can keep 96.5%of the original after bending for 1000 cycles at a radius of 4.45 mm and a strain of 2.2%.This work puts forward a feasible guidance in designing electrode and choosing appropriate additives for high performance flexible all-inorganic green Pe LEDs.