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...

Hybrid perovskites are emerging as highly efficient materials for optoelectronic applications, however, their operational lifetime has remained a limiting factor for their continued progress. In this work, perovskite light emitting electrochemical cells (PeLECs) utilizing an optimized fraction of LiPF 6 salt additive exhibit enhanced stability. At 0.5 wt% LiPF 6 , devices exhibit 100 h operation at high brightness in excess of 800 cd m −2 under constant current driving, achieving a maximum luminance of 3260 cd m −2 and power efficiency of 9.1 Lm W −1 . This performance extrapolates to a 6700 h luminance half-life from 100 cd m −2 , a 5.6-fold improvement over devices with no LiPF 6 . Analysis under constant voltage driving reveals three current regimes, with lithium addition strongly enhancing current in the second and third regimes. The third regime correlates lower rates of luminance with lowered current flow. These losses are mitigated by LiPF 6 addition, an effect postulated to arise from preservation of perovskite structure. Electrochemical impedance spectroscopy with equivalent circuit modeling revealed that electrical double layer widths are minimized at 0.5 wt% LiPF 6 and inversely correlate with efficient performance. These results demonstrate that an optimal LiPF 6 concentration improves stability and efficiency through improved double layer formation and retention of perovskite structure.

Hybrid organic–inorganic lead halide perovskites have attracted much attention in the field of optoelectronic devices because of their desirable properties such as high crystallinity, smooth morphology, and well-oriented grains. Recently, it was shown that thermal nanoimprint lithography (NIL) is an effective method not only to directly pattern but also to improve the morphology, crystallinity, and crystallographic orientations of annealed perovskite films. However, the underlining mechanisms behind the positive effects of NIL on perovskite material properties have not been understood. In this work, we study the kinetics of perovskite grain growth with surface energy calculations by first-principles density functional theory (DFT) and reveal that the surface energy-driven preferential grain growth during NIL, which involves multiplex processes of restricted grain growth in the surface-normal direction, abnormal grain growth, crystallographic reorientation, and grain boundary migration, is the enabler of the material quality enhancement. Moreover, we develop an optimized NIL process and prove its effectiveness by employing it in a perovskite light-emitting electrochemical cell (PeLEC) architecture, in which we observe a fourfold enhancement of maximum current efficiency and twofold enhancement of luminance compared to a PeLEC without NIL, reaching a maximum current efficiency of 0.07598 cd/A at 3.5 V and luminance of 1084 cd/m2 at 4 V.

Metal halide perovskites have emerged as promising gain materials for on-chip lasers in photonic integrated circuits. For these to become commercially relevant as economical on-chip light sources, a clear onset of quasi-continuous wave (quasi-CW) and, eventually, continuous wave (CW) lasing at room temperature or Peltier-cooling accessible temperatures from directly patterned perovskite cavities is a critical milestone that must be achieved. Herein, through directly patterning with nanoimprint lithography and encapsulation of the cavity with a thin layer of polycarbonate (PC), quasi-CW lasing from CH 3 NH 3 PbBr 3 (MAPbBr 3 ) is demonstrated up to 260 K. The PC layer is also shown to effectively encapsulate the surface defects of MAPbBr 3 and protect devices from environmental hazards. Through the combined analysis of the crystal quality, degradation process during optical pumping, defect encapsulation, and laser performance, room temperature CW lasing from directly patterned perovskite cavities should be within reach.

Hybrid organic–inorganic perovskite light‐emitting devices (LEDs) have recently shown the characteristic dynamical behavior of light‐emitting electrochemical cells (LECs), with intrinsic ionic migration creating an electric double layer and internal p‐i‐n structure and by accumulation of ions at interfaces. Therefore, the development of perovskite light‐emitting and photovoltaic devices based on the concepts of LEC operation attracts much attention and clarifies general physical processes in perovskites. Here, new directions that can further improve perovskite optoelectronic devices and extend their functionalities using additive mobile ions are overviewed: 1) enhancing single‐layer LECs with lithium additives for increased efficiency and longer lifetime; 2) facilitating ionic motion in three‐layer perovskite LECs to create dual‐functional devices, operating as both LEC and solar cells; and 3) creating truly ambipolar LEC devices with carbon nanotubes as stable electrodes that leverage ionic doping. Taken together, the use of these approaches provides a strategy to create efficient, stable, and bright LECs, which use advantages of both LED and LEC operation. It is discussed that how the LEC behavior in perovskite LEDs can be further improved to address the long‐term challenges in perovskite optoelectronics, such as stability, through approaches like ionically reconfigurable host/guest systems.