Degradation Mechanism of Perovskite Light‐Emitting Diodes: An In Situ Investigation via Electroabsorption Spectroscopy and Device Modelling

Abstract

The past few years have seen a significant improvement in the efficiency of organometal halide-perovskite-based light-emitting diodes (PeLEDs). However, poor operation stability of the devices still hinders the commercialization of this technology for practical applications. Despite extensive studies on the degradation mechanisms of perovskite thin films, it remains unclear where and how degradation occurs in a PeLED. Electroabsorption (EA) spectroscopy is applied to study the degradation process of PeLEDs during operation and directly evaluates the stability of each functional layer (i.e., charge transporting layers and light-emitting layer) by monitoring their unique optical signatures. The EA measurements unambiguously reveal that the degradation of the PeLEDs occurs predominantly in the perovskite layer. With finite-element method-based device modeling, it is further revealed that the degradation may initiate from the interface between the perovskite and hole transporting layers and that vacancy, antisite, or interstitial defects can further accelerate this degradation. Inspired by these observations, a surface-treatment step is introduced to passivate the perovskite surface with phenethylammonium iodide. The passivation leads to a drastic enhancement of the PeLED stability, with the operation lifetime increased from 1.5 to 11.3 h under a current density of 100 mA cm −2 .light emission properties of PeLEDs, and the external quantum efficiency (EQE) and radiance of the best -performing nearinfrared PeLED has already reached 21.6% and 308 W (sr × m 2 ) −1 , respectively. [4] However, most reported PeLEDs degrade rapidly during operation, losing luminescence within several hours. [5][6][7] Stability has been a general issue for almost all perovskite-based optoelectronic devices, but it is particularly problematic in PeLEDs where the current density is high and the energy conversion efficiency is still low. Some research efforts have been made to study the degradation mechanisms of perovskite solar cells and LEDs through characterization of perovskite films, which include in situ X-ray diffraction (XRD) monitoring of phase evolution, [8][9][10][11][12][13] time-of-flight secondary ion mass spectrometry investigation of water penetration in perovskite films, [14] and time-resolved photoluminescence measurements. [12] Prakasam et al. peeled off the top electrode layer of a PeLED after bias stressing and studied the underlying perovskite layer using scanning electron microscopy, structural characterization techniques, and energy-dispersive X-ray profiling. [15] The results suggest decomposition of the perovskite layer during operation, leading to local delamination of the top electrode layer. Studies have also been done to directly improve the stability of the perovskite layer through selection of stable cations, [16] composition tuning and inclusion of additives in the precursor, [17] as well as introduction of a doped electron transport layer, [18] and development of a core-shell perovskite grain structure. [7] De...

Perovskite Light Emitting Diode Characteristics: The Effects of Electroluminescence Transient and Hysteresis

“…It can be observed in many PeLEDs in literature during lifetime measurements, with the stressing time spanning a wide range of timescales from few minutes to several hours. [ 8,20,21 ]…”

Phenylalkylammonium passivation enables perovskite light emitting diodes with record high-radiance operational lifetime: the chain length matters

“… 27 ). In our previous study 28 , we found that the ion diffusion at the interface between the perovskite and its top neighboring organic hole-transporting layer plays a critical role in the degradation process of PeLEDs. It is worth noting that to date almost all surface passivation or ligand engineering research of PeLEDs focuses on defect passivation, instead of ion-blocking.…”

Degradation and self-repairing in perovskite light-emitting diodes

“…15,16 In addition, based on previous investigations of perovskite solar cells, field-dependent ion migration and relevant material/interfacial degradation have been regarded as the most critical factors limiting the reliability of PeLEDs. [17][18][19][20][21] As such, there have been extensive efforts to improve the operational lifetime by immobilizing the ions, including perovskite composition engineering, 22 defect passivation, and construction of mixed-dimensional structures. 3,5,[23][24][25] Nevertheless, a deep understanding of how ion-drifting influences PeLEDs' performance in detail remains missing, hindering targeted material design and device optimization for further improvement of the operational lifetime.…”