3D and 2D Metal Halide Perovskites for Blue Light-Emitting Diodes

Abstract

Metal halide perovskites (MHPs) are emerging next-generation light emitters that have attracted attention in academia and industry owing to their low material cost, simple synthesis, and wide color gamut. Efficient strategies for MHP modification are being actively studied to attain high performance demonstrated by commercial light-emitting diodes (LEDs) based on organic emitters. Active studies have overcome the limitations of the external quantum efficiencies (EQEs) of green and red MHP LEDs (PeLEDs); therefore, the EQEs of PeLEDs (red: 21.3% at 649 nm; green: 23.4% at 530 nm) have nearly reached the theoretical limit for the light outcoupling of single-structured planar LEDs. However, the EQEs of blue PeLEDs (12.1% at 488 nm and 1.12% at 445 nm) are still lower than approximately half of those of green and red PeLEDs. To commercialize PeLEDs for future full-color displays, the EQEs of blue MHP emitters should be improved by approximately 2 times for sky-blue and more than 20 times for deep-blue MHP emitters to attain values comparable to the EQEs of red and green PeLEDs. Therefore, based on the reported effective approaches for the preparation of blue PeLEDs, a synergistic strategy for boosting the EQE of blue PeLEDs can be devised for commercialization in future full-color displays. This review covers efficient strategies for improving blue PeLEDs using fundamental approaches of material engineering, including compositional or dimensional engineering, thereby providing inspiration for researchers.

Effect of the hole transport layer on the performance of sky-blue Dion–Jacobson perovskite light-emitting diodes

“…Metal halide perovskites hold great potential for light-emitting diode (LED) applications [1][2][3][4][5][6][7][8][9][10][11][12] due to their exceptional properties, such as tunable emission, high luminescence efficiency, low cost, and simple processes for large-area device fabrication. [1][2][3][4][5] While high external quantum efficiencies (EQEs) approaching or even exceeding 25% have been achieved for perovskite LEDs (PeLEDs) in green and red spectral regions, 8,10,11 the efficiency of blue PeLEDs is still lagging behind. [5][6][7][8][9]11,12 In addition, the blue PeLEDs also commonly suffer from instability issues, such as short lifetime and spectral instability, i.e.…”

“…[1][2][3][4][5] While high external quantum efficiencies (EQEs) approaching or even exceeding 25% have been achieved for perovskite LEDs (PeLEDs) in green and red spectral regions, 8,10,11 the efficiency of blue PeLEDs is still lagging behind. [5][6][7][8][9]11,12 In addition, the blue PeLEDs also commonly suffer from instability issues, such as short lifetime and spectral instability, i.e. shift of the emission wavelength over time.…”

“…1,12,17 In general, the emission wavelength of a quasi-2D PeLED is typically controlled by adjusting the ratio of the bulky spacer cation and small cation, which results in a variation in the distribution of different n phases. 5,11,12 However, it is commonly needed to employ additional methods to simultaneously achieve blue emission and efficient funneling since this requires not only the suppression of the formation of the n = 1 phase which leads to inefficient funneling but also the suppression of formation of n 4 4 phases which would lead to green emission. 12 One of the approaches to optimize crystallization and phase composition of a quasi-2D perovskite film is spacer cation mixing.…”

“…Since DJ perovskites are highly promising, it is of interest to carefully optimize the film composition to achieve blue emission from a DJ perovskite emitter for PeLED applications. As the mixing of spacer cations gives rise to an improved optimization of phase composition, 1,5,9,12,17,22 we explored the use of mixed diammonium spacer cations, short-chain methylenediammonium (MDA) and long-chain decanediammonium (DDA) to achieve sky-blue emission. The choice of short chain cations, such as MDA, and long chain cations, such as DDA, enables tuning of the phase composition by suppressing the formation of undesirable low n (n = 1) and high n (n 4 4) phases.…”

“…12 One of the approaches to optimize crystallization and phase composition of a quasi-2D perovskite film is spacer cation mixing. 1,5,9,17,22 The spacer cation mixing approach has been used in different quasi-2D materials, including those involving monovalent spacer cations, 1,5,17 divalent spacer cations, 22 and the mixture of monovalent and divalent spacer cations. 9,14 Different spacer cations will have different interactions among the spacer cations, which can affect the formation of low n phases, in particular undesirable n = 1 phase.…”