Improving Efficiency and Stability in Quasi-2D Perovskite Light-Emitting Diodes by a Multifunctional LiF Interlayer

Abstract

Owing to the enlarged exciton binding energy and the ability to confine charge carriers compared to their three-dimensional (3D) counterparts, research on quasi-two-dimensional (quasi-2D) perovskite materials and the correlative application in light-emitting diodes (LEDs) has attracted considerable attention. However, high density of defects, exciton emission trapping, and unbalanced charge injection are still the main intractable obstacles to their further development and practical application. Herein, we report an efficient multifunctional interlayer, lithium fluoride (LiF), to boost the performance of green-emitting quasi-2D perovskite LEDs (PeLEDs) by simultaneously overcoming the aforementioned issues. The introduced LiF interlayer not only eliminates the defects at perovskite grain boundaries and the surface by reinforcing the chemical bonds with uncoordinated lead ions but also restrains the emission of perovskite from quenching triggered by the electron transport layer and reduces excess electron injections to effectively balance carriers in the device. As a result, the resulting green quasi-2D PeLED shows a maximum external quantum efficiency of 16.35%, which is the best value obtained for quasi-2D perovskite-based LEDs reported so far, with simultaneous improvement in the operating lifetime of the device.

Enhanced Light Emission Performance of Mixed Cation Perovskite Films—The Effect of Solution Stoichiometry on Crystallization

“…[6] However, despite these advantages, the achieved efficiencies of quasi-2D perovskite-based LEDs have been limited by nonoptimized distributions of different n phases, and increased defects at surface or grain boundaries. [7] The common approaches to increasing the efficiency of quasi-2D LEDs include optimizing the film composition or deposition to optimize the distribution of quasi-2D phases with different n to achieve efficient funnelling, [2,4,5,6,10,12] using post-treatments to remove excess spacer cations, [8] optimizing the device architecture, [3,9] or using additives to passivate defects. [7,15] The optimization of the film composition would typically involve the optimization of the solution stoichiometry, as well as the choices of spacer cations R + and small cations B + .…”

“…[7,15] The optimization of the film composition would typically involve the optimization of the solution stoichiometry, as well as the choices of spacer cations R + and small cations B + . Various spacer cations have been reported to date, and common choices involve alkyl chain spacers such as butylammonium (BA), which yielded efficiencies ranging from ≈7% to 16%, [8,9,12,13,18] as well as aromatic spacers such as phenethylamine (PEA), which yielded efficiencies in the range %7-15%. [3][4][5][6][7] Among possible small cations A + , all three possible choices, namely Cs, [2,8,9,11] formamidinium (FA), [3,6,12] and methylammonium (MA), [4,5,18] have been reported.…”

“…Various spacer cations have been reported to date, and common choices involve alkyl chain spacers such as butylammonium (BA), which yielded efficiencies ranging from ≈7% to 16%, [8,9,12,13,18] as well as aromatic spacers such as phenethylamine (PEA), which yielded efficiencies in the range %7-15%. [3][4][5][6][7] Among possible small cations A + , all three possible choices, namely Cs, [2,8,9,11] formamidinium (FA), [3,6,12] and methylammonium (MA), [4,5,18] have been reported. Recently, the use of mixed cations has been proposed as a feasible method to control the crystallization and consequently film composition and emission efficiency.…”

Operationally Stable Perovskite Light Emitting Diodes with High Radiance

“…[ 16,34 ] On the contrary, both PCBM and ZnMgO have much higher electron mobility (>10 −3 cm 2 V −1 s −1 ) compared to TPBi. [ 35 ] Moreover, as is shown in Figure a,b, although near‐ohmic contacts were previously reported for both the TPBi/LiF/Al and PCBM/ZnMgO/Al cathodes, [ 36,37 ] the shallower lowest unoccupied molecular orbital (LUMO) level of TPBi (−2.7 eV) than that of PCBM/ZnMgO (around −4.0 eV) results in a higher V bi for the TPBi/LiF devices. Therefore, the PCBM/ZnMgO device reaches flat‐band condition and a significant amount of charge injection at a much lower voltage bias, achieving a lower turn‐on voltage than that of TPBi/LiF.…”

Light‐Emitting Perovskite Solar Cells: A Tale of Two States

“…[1][2][3][4][5][6][7][8][9] Aside from photovoltaic applications, MHPs have high photoluminescence quantum efficiency (PLQY), low exciton binding energy, and high color purity, which render them an ideal candidate for the development of high-performance light-emitting diodes (LEDs). [10][11][12][13][14][15][16] Interestingly, as both perovskite LEDs and SCs have similar geometry and use the same semiconductor, therefore, perovskite light-emitting solar cells (LESCs), which can perform both functions by acting as a reversible transducer between light and electricity, hold the ultimate device architecture in the optoelectronics industry. When integrated with a rechargeable battery, these LESCs can be used in solar lamps, which harvest solar energy during the day as SCs and emit light at night as LEDs.…”