Bright and Effectual Perovskite Light-Emitting Electrochemical Cells Leveraging Ionic Additives

Abstract

Perovskite light emitting diodes (PeLEDs) have drawn considerable attention for their favorable optoelectronic properties. Perovskite light emitting electrochemical cells (PeLECs)-devices that utilize mobile ions -have recently been reported but have yet to reach the performance of the best PeLEDs. We leveraged a poly(ethylene oxide) electrolyte and lithium dopant in CsPbBr3 thin films to produce PeLECs of improved brightness and efficiency. In particular, we found that a single layer PeLEC from CsPbBr3:PEO:LiPF6 with 0.5% wt. LiPF6 produced highly efficient (22 cd/A) and bright (~15000 cd/m 2 ) electroluminescence. To understand this improved performance among PeLECs, we characterized these perovskite thin films with photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD).These studies revealed that this optimal LiPF6 concentration improves electrical double layer formation, reduces the occurrence of voids, charge traps, and pinholes, and increases grain size and packing density. TOC GRAPHICSPerovskite light-emitting diodes (PeLEDs) based on inorgano−organometallic halide perovskites, such as CH3NH3PbX3 and CsPbX3 (X = Cl, Br, or I), have attracted much attention due to their low-temperature solution processability, high color purity with narrow spectral width (FWHM of 20 nm), band gap tunability and large charge carrier mobility. [1][2][3][4] To date, devices based on these perovskites have achieved high luminance in excess of 10000 cd/m 2 with high efficiencies (EQE ~10%), comparable to organic LEDs and quantum dot (QD) LEDs. [1][2][3][4][5][6][7] Interestingly, effects such as hysteresis and high capacitance in perovskite semiconductor devices suggest that ion motion can largely influence device operation. In this vein, researchers have recently been investigating perovskite materials in light-emitting electrochemical cell (LEC) architectures instead of traditional LEDs. [8][9][10][11] These LEC devices (PeLEC leverage ion redistribution to achieve balanced and high carrier injection, resulting in high electroluminescence efficiency. Due to this mechanism, LEC devices can be prepared from a simple architecture consisting of a single semiconducting composite layer sandwiched between two electrodes. In addition, they can operate at low voltages below the bandgap, yielding highly efficient devices.Recently, perovskite LECs (PeLECs) have been reported and show promise as electroluminescent devices. [8][9][10][11] However, these PeLECs are generally limited to luminance maxima of 1000 cd/m 2 or lower, below what has been typically observed in PeLEDs. This disparity suggests that further understanding and refinement of PeLEC materials and devices could produce significant improvements of brightness, efficiency, and other performance metrics. To this end, we fabricated a highly efficient (22 cd/A) and bright (~15000 cd/m 2 ) single layer LEC based on a cesium lead halide perovskite, CsPbBr3. To achieve...

Color‐Stable, Efficient, and Bright Blue Light‐Emitting Electrochemical Cell Using Ionic Exciplex Host

“…A wide variety of emitting materials, [ 2,6,7 ] such as fluorescent polymers and small molecules, [ 1,8,9 ] phosphorescent ionic transition‐metal complexes, [ 10–14 ] thermally‐activated delayed fluorescence (TADF) molecules, [ 15–17 ] quantum dots, [ 18 ] and perovskite, [ 18–20 ] have been used for LECs. With these emitting materials, red to blue and white LECs have been fabricated.…”

Reconfigurable Perovskite LEC: Effects of Ionic Additives and Dual Function Devices

“…The inset shows the EL of an optimal 0.5 wt% LiPF 6 device at a bias of 5 V. a,b,e) Reproduced with permission. [ 32 ] Copyright 2019, American Chemical Society. c,d) Reproduced with permission.…”

“…In the last several years, inspired by conventional LEC concepts, some research has been started on the use of perovskite materials in the conventional SL‐LEC‐type architecture (however without adding external ions or electrolytes) instead of traditional multilayer OLED design. [ 28–35 ] Such initial PeLEC/LEDs leveraged some advantages of internal ionic species (cations: MA + , Cs + , anions: I − , Br − , and their vacancies V + , V − ) redistribution in pure perovskites to achieve balanced and high carrier injection, resulting in high EL efficiency in single‐layer devices. Here, we call these devices as SL‐PeLEC/LED, since they have been based on a solely intrinsic perovskite ionic migration processes—with some solid polymer composite sandwiched between two electrodes.…”

“…are necessarily added, as opposed to conventional LEC/LED‐type initial architectures of SL‐PeLEC/LED which relied only on the migration of intrinsic ionic species of the perovskite. [ 28–35 ] Particularly, we overview the efforts on air‐stable and halogen‐stable electrodes, true SL‐PeLECs with higher brightness and efficiency, enhanced stability and longer lifetime, as well as their further optimization via in situ p‐i‐n structure formation by external ions. [ 43–46 ] Figure shows the key concepts for the creation of an efficient and bright true PeLEC.…”

Halide perovskite nanotube toward energy applications: A first‐principles investigation

“…Apart from solar cell applications, the halide perovskite materials have been identified to be suitable candidates for many other energy systems . For example, they exhibit good ion diffusion properties and lithium storage performance, which could be utilized for energy storage systems such as lithium‐ion battery and lithium‐sulfur battery.…”