Carbon Dots Induced Room Temperature Crystallization Of Quasi-two-dimensional Perovskite For Light-emitting Diodes

Metal halide perovskites have been widely used in solar cells,light-emitting diodes(LEDs)and other fields requiring adjustable band gaps,solution-processability,simple technology,and high carrier mobility.Compared to three-dimensional perovskites,quasi-two-dimensional perovskites are considered the most promising material for perovskite LEDs because they combine high exciton binding energy,high carrier mobility,and excellent stability.A thermal annealing process is currently used to remove excess solvent and accelerate the formation of a dense,complete quasi-two-dimensional perovskite film.However,this process increases the complexity of the preparation process of perovskite light-emitting layer and affects the process of device industrialization.Therefore,the realization of crystallization at room temperature is of great significance for exploring the crystal growth mechanism of quasi-two-dimensional perovskite and accelerating the industrialization of perovskite optoelectronic devices.Among all the methods to regulate the crystallization of perovskite,the interaction between potassium ions and halogen ions in perovskite is the most effective for regulating the crystallization of perovskite.Compared with other additives doped into perovskite,the surface of carbon dots can be covered with a variety of functional groups,and the synthesis method is simple and it is stable.It is more suitable for optoelectronic parts to achieve crystallization regulation,passivation defects,improvement of interface infiltration and other functions.In order to achieve the preparation of high-quality perovskite films at room temperature,a new multifunctional interfacial modification layer of carbon dots passivated by potassium ions was introduced onto the surface of the hole transport layer to regulate the crystallization properties of quasi-two-dimensional perovskite films.With carbon dots as the heterogeneous nucleation center,the non-annealing crystallization of perovskite is realized,and this non-annealing film is applied to light-emitting diodes.The influence of the introduction of a carbon dots interface layer and a non-annealing perovskite film on device performance is studied.The main research contents are as follows:1.Based on the reaction system of citric acid and urea,the surface potassium passivated carbon dots were synthesized by solvothermal and surface post-treatment.The synthesized carbon dots are spherical nanoparticles with a particle size distribution of 2-3 nm,and some graphitized carbon cores have large localπ-conjugated centers,which are beneficial to carrier transport.The nanostructure of carbon dots and the abundant surface functional groups such as potassium ions,carbonyl groups,and amino groups can be used as nucleation centers to induce the crystallization of perovskite and passivation defects and give the carbon dots excellent solubility.Combined with the semiconductor properties of carbon dots and their interaction with adjacent functional layers,the device can improve carrier injection and transport,which is beneficial to the application of perovskite LED as a multifunctional interface material,which can improve device performance in multiple dimensions.2.A potassium ion passivated carbon dot film was applied between PEDOT:PSS and perovskite layers as the interface modification layer.The study confirmed that the introduction of a carbon dot interface layer can effectively improve the crystallinity of unannealed perovskite film and improve the film quality,thus improving the fluorescence efficiency and lifetime of the film,and reducing the non-radiation recombination rate.It is beneficial to achieve high electroluminescence performance.The mechanism of rapid nucleation and crystallization of perovskite precursors induced by the carbon dots interface layer during spinning coating at room temperature was further explored so that quasi-two-dimensional perovskite films with good crystallizability could be prepared without annealing.3.The carbon dots interface modification layer and the perovskite film induced by room temperature growth are applied to the light emitting diodes,and the influence of the introduction of the carbon dots interface layer and the room temperature crystallized perovskite film on the energy level,carrier injection,transmission,and electroluminescence performance is studied.The turn-on voltage,maximum brightness,and maximum external quantum efficiency of the optimized green light device are 2.9 V,52000 cd/m~2,15.4%,respectively.The performance of the optimized green light emitting device can exceed that of the conventional perovskite thermal annealing device without the carbon dots interface layer because the perovskite layer grown on the carbon dots interface layer has a high-quality crystalline film.The addition of a carbon dots interface layer improves overall carrier injection and transmission.To sum,using the multi-functional carbon dots design in this paper,high-quality crystalline perovskites were successfully spin-coated at room temperature to form quasi-two-dimensional perovskite films.Using a carbon dots interface layer and crystalline perovskite films at room temperature,a quasi-2D perovskite LED with superior electroluminescence performance has been demonstrated.This perovskite film is prepared without annealing and its light-emitting diodes provide a novel idea for perovskite film and LED preparation.