Elucidating and Mitigating Degradation Processes in Perovskite Light‐Emitting Diodes

Abstract

cells, lasers, detectors, and light-emitting diodes (LEDs) owing to their exceptional optical and electronic properties such as long charge-carrier diffusion lengths, high absorption coefficients, tunable bandgaps, and facile processing. [1-4] For bulk polycrystalline perovskite thin films, one of the key approaches to boost the stability and optoelectronic properties is through employing mixtures of A-site cations, such as methylammonium (MA), formamidinium (FA), and cesium (Cs) [5,6] as well as mixtures of X-site anions, such as bromide (Br) and iodide (I). [7,8] Recently, rapid progress has been made in improving the performances of perovskite light-emitting diodes (PeLEDs), [9-14] yet their practical commercial implementation is still severely hindered by poor operational lifetimes. [10,15-19] Although the sensitivity of the devices to atmospheric effects such as oxygen and water can be mitigated through effective packaging techniques, [20] there is also an intrinsic instability in the devices with the high electric fields experienced under LED operation. [21] This instability appears to be caused by a combination of ionic migration and Joule heating, [20,22-26] which ultimately leads to degradation of the device performance. In order to overcome these degradation

Nanosecond‐Pulsed Perovskite Light‐Emitting Diodes at High Current Density

“…Films containing PMAI additive exhibit small grain sizes of < 20 nm (Figure 4g), while larger grain sizes are found for the stoichiometric MAPbI 3 films (50-195 nm) and films containing KI additive feature larger grain sizes (70-220 nm) (Figure 4a,d). It has been established that the KI additives can efficiently passivate defects and reduce first-order defect-assisted nonradiative recombination in perovskites, [27][28][29][30][31] while the PMAI additives can both passivate defects and enhance electron-hole capture rate at low current density (e.g., < 100 mA cm −2 ). [4,19] On the other hand, the influence of perovskite compositions corresponding current pulses shown in Figure S5, Supporting Information.…”

Halide Perovskite Light‐Emitting Diode Technologies

“…[114] On the other hand, irreversible accumulation of ions at an interface is observed in mixed halide PeLEDs, leading to charge-carrier injection barriers and nonradiative recombination. [129] The low formation energy of perovskite materials and the complex electrochemistry at the device interfaces remain big concerns for commercial lightemitting applications. [130,131] It is widely known that halide perovskites suffer from photoinstabilities, showing both photobrightening and photodarkening effects.…”

“…[ 133 ] This phenomenon is observed in EL leading to a “burn‐in” or “luminance overshoot” under operation attributed to ionic reorganization in perovskites that can be maintained for longer periods of operation with appropriate passivation. [ 129,134,135 ] Interestingly, some groups have taken advantage of this phenomenon to propose perovskite‐based light‐emitting electrochemical devices, [ 136 ] opening new avenues for these materials. [ 137 ] It remains to be seen if such approaches can stabilize operation over long periods, including mitigating against redox chemistry in these ionic systems in the presence of high densities of injected electrons under operating conditions—but such breakthroughs will be critical for realizing long‐term stability.…”

Characterize and Retard the Impact of the Bias‐Induced Mobile Ions in CH3NH3PbBr3 Perovskite Light‐Emitting Diodes

“…[10,34,35] Numerous works have reported that the EQE of PeLEDs increases with the bias voltage, current density, and subsequent scans during the electric bias. [36][37][38][39][40][41] We usually observed that both magnitudes of the electroluminescence (EL) and efficiencies are very low while PeLEDs are operated at the low electric bias, but significantly increased at the high bias regime. [42,43] Such observations deviate the ideal current density-luminescence-voltage (J-L-V) characteristics for decent light-emitting diodes (LEDs) with a relatively high magnitude of EQE.…”