Study On Light-emitting Diodes And Spectral Regulation Based On CsPbI₃ Quasi Two-dimensional Perovskite Films

Color display technology is generally realized by RGB display technology,that is,based on red,green and blue LEDs,color development patterns are obtained through current and other conditions.This display technology has been applied from the most traditional liquid crystal display to the most advanced Mini LED and Micro LED imaging field.Quasi two-dimensional（Q-2D）perovskite has been widely used in LED because of its high carrier transmission efficiency,multi quantum well structure and good radiation recombination efficiency.The Q-2D perovskite takes A′₂A_n-1B_nX_3n+1 as the molecular formula and is expressed as a layered perovskite mixture with different layers in the film.In the formula,the n value corresponds to the number of[BX₆]^4-octahedral layers sandwiched between organic cations A′,and the perovskite with different n values in the Q-2D perovskite spontaneously forms a quantum well structure due to its different band gap,The material has ultra-high energy transfer efficiency and realizes high-performance luminescence.Pure red LED is indispensable in display devices based on RGB display principle.However,most of the existing perovskite LED brightness is very low,only a few hundred cd·m^-2;Moreover,LEDs based on perovskite materials as the light-emitting layer often use halogen hybridization to tune the light-emitting spectrum from dark red（～700 nm）to pure red（630-660 nm）.However,this tuning method will bring serious halogen offset,which will also significantly reduce the light-emitting stability and service life of the device.In this paper,a series of Q-2D perovskite films were prepared by one-step method to learn the influence of long-chain amine on Q-2D films,Q-2D perovskite materials with good fluorescence properties were selected as the light-emitting layer to construct dark red LED.Finally,a new pure red photoelectric spectrum tuning method was proposed,the devices have stable pure red luminescence and good luminescence performance.Q-2D CsPbI₃ perovskite films based on PEAI,4-F-PEAI and 4-F-PMAI were prepared by one-step spin coating method.The effects of the types and addition ratio of long-chain amines on the microstructure,optical properties and stability of the films were studied,and the mechanism of the effect of long-chain amines on the growth of Q-2D CsPbI₃ perovskite films was clarified.It is found that Q-2D perovskite films with low n value are easy to be formed when the proportion of long-chain amine is small;Increasing the proportion of long-chain amine,the Q-2D perovskite with large n value is gradually produced;Further increasing the proportion of long-chain amine,the proportion of large n-value Q-2D perovskite phase gradually decreases,and finally a Q-2D CsPbI₃ perovskite mixture dominated by low n-phase is formed.F-based hybrid and short chain long-chain amine structure can improve the crystallinity of Q-2D perovskite films.The phase content of different n values in the phase structure is more uniform,accompanied by relatively high content of large n phase and less content of small N phase.The PLQY of Q-2D CsPbI₃ perovskite films was as high as 21%when 60%4-F-PMAI was added;The 4-F-PEAI based Q-2D perovskite with F and long chain has better thermal stability and air stability,and the n=1 phase perovskite has the best stability in the Q-2D perovskite mixed phase.Based on the Q-2D CsPbI₃ perovskite films with different long-chain amines,the Q-2D perovskite LED is constructed.The influence of the type and content of long-chain amines on the performance of perovskite LED is clarified.It is found that the perovskite LED with uniform n-value perovskite distribution,a small amount of small n-phase and a large amount of large n-phase has better luminescence performance.The short chain length and F-group hybridization of 4-F-PMAI improve the phase structure of quasi two-dimensional CsPbI₃ perovskite film.When the addition of 4-F-PMAI is 60%,the LED device has an external quantum efficiency of3.64%,which is higher than that of 0.2%and 0.39%of PEAI and 4-F-PEAI.The annealing temperature of Q-2D perovskite films and the thickness of Li F and PEDOT were further optimized.A Q-2D deep red CsPbI₃ perovskite LED with external quantum efficiency of 7.02%,maximum brightness of 576.8 cd·m^-2 and light-emitting peak position of 691 nm was prepared.Combined with the"A-site"cation and halogen doping strategy,the emission spectrum of Q-2D CsPbI₃ perovskite thin film red LED was adjusted.By changing the Rb/CS and Br/I ratio in the precursor solution,The luminescence spectrum is from deep red（691 nm）to pure red（656 nm）.At the optimized Rb/CS and Br/I ratio,Rb_0.3Cs_0.7Pb Br_0.7I_2.3 perovskite pure red LED with Q-2D structure is obtained.The peak external quantum efficiency is 3.18%and the maximum brightness is 1327.2 cd·m^-2,which reaches the forefront of the reported pure red Q-2D perovskite LED brightness.The color coordinate of pure red LED is（0.708,0.292）with extremely high color purity.It is one of the studies that most accord with the international rec.2020 standard（0.708,0.292）color coordinate.RB/CS cation alloying and halogen doping cooperate It overcomes the spectral instability of traditional pure red light-emitting diodes and obtains a stable EL spectrum.The device life is 8 times that of the device based on halogen anion exchange tuning method,up to 29 min.