Stabilizing Perovskite Light‐Emitting Diodes by Incorporation of Binary Alkali Cations

Abstract

high-performance LEDs due to high photoluminescence (PL) quantum efficiency, narrow emission linewidth (i.e., high color purity), and low density of sub-gap electronic trap states. [6][7][8][9] Significant breakthroughs have been achieved in perovskite LEDs (PeLEDs) in the past 5 years, with the external quantum efficiency (EQE) boosted from 0.76% in 2014 to over 21% recently, [1,10,11] comparable to the stateof-the-art performance of organic LEDs (OLEDs). [12] Nevertheless, despite rapid development of electroluminescence (EL) efficiency, the commercialization of PeLEDs is still challenging due to the poor device stability, [13] which mainly stems from degradation of perovskite materials upon air exposure or electrical bias. As demonstrated in perovskite-based photovoltaic (PV) devices, migration of mobile ions under electrical bias stress causes destruction of the perovskite lattices and infiltration of mobile ions into adjacent layers. [14,15] In PeLEDs, a higher electricfield is present and may aggravate the ion migration issue. In particular, in contrast to the thick perovskite absorber layer in PV devices, the perovskite light-emitting layer in PeLEDs is much thinner (typically a few tens of nanometers) as required for spatial confinement of charge carriers and efficient radiative recombination. [1] Therefore, mobile ions in the thin perovskite layer would be The poor stability of perovskite light-emitting diodes (PeLEDs) is a key bottleneck that hinders commercialization of this technology. Here, the degradation process of formamidinium lead iodide (FAPbI 3 )-based PeLEDs is carefully investigated and the device stability is improved through binary-alkalication incorporation. Using time-of-flight secondary-ion mass spectrometry, it is found that the degradation of FAPbI 3 -based PeLEDs during operation is directly associated with ion migration, and incorporation of binary alkali cations, i.e., Cs+ and Rb + , in FAPbI 3 can suppress ion migration and significantly enhance the lifetime of PeLEDs. Combining experimental and theoretical approaches, it is further revealed that Cs + and Rb + ions stabilize the perovskite films by locating at different lattice positions, with Cs + ions present relatively uniformly throughout the bulk perovskite, while Rb + ions are found preferentially on the surface and grain boundaries. Further chemical bonding analysis shows that both Cs + and Rb + ions raise the net atomic charge of the surrounding I anions, leading to stronger Coulomb interactions between the cations and the inorganic framework. As a result, the Cs + -Rb + -incorporated PeLEDs exhibit an external quantum efficiency of 15.84%, the highest among alkali cation-incorporated FAPbI 3 devices. More importantly, the PeLEDs show significantly enhanced operation stability, achieving a half-lifetime over 3600 min.In recent years, solution-processed metal halide perovskites have attracted tremendous interests in the scientific community including the field of light-emitting diodes (LEDs). [1][2][3][4][5] Besides low fab...

Elucidating and Mitigating Degradation Processes in Perovskite Light‐Emitting Diodes

“…This generalized template is consistent with other recent strategies successfully stabilizing PeLED operation including use of 2D molecules and Cs/Rb components. [26,40] In conclusion, using a combination of in-and ex situ device, nanoscale cross-sectional chemical mapping, and optical spectroscopy measurements, we found that the reduction in the performance and luminescence yield of (Cs 0.06 FA 0.79 MA 0.15 ) Pb(I 0.85 Br 0.15 ) 3 PeLED devices arises from an accumulation of bromide content at one interface and a more iodide-rich bulk material. This accumulation of ions leads to a defective perovskite layer that acts as an injection barrier for charge carriers and leads to increased nonradiative recombination.…”

“…Passivation with alkali metals such as potassium have been previously shown to reduce nonradiative losses and ion migration in perovskite devices. [ 29–40 ] We prepared a series of passivated perovskite thin films by addition of different amounts of potassium iodide solution (in the range x = 0–0.44, where x is the fraction of potassium out of total monovalent cations; [K]/([K] + [MA] + [FA] + [Cs])) to different iodide/bromide composition solutions to explore the series (Cs 0.06 FA 0.79 MA 0.15 )Pb(I 1− y Br y ) 3 , with y = 0–1 being the fraction of bromide out of total halide (with corresponding PL emission peaks spanning 560 to 826 nm, see Figure S7, Supporting Information). To assess the resilience of the resulting films to photo‐induced ion migration, we monitored the PL spectra of the films before and after continuous illumination at ≈60 mW cm −2 over a period of 30 min.…”

“…This generalized template is consistent with other recent strategies successfully stabilizing PeLED operation including use of 2D molecules and Cs/Rb components. [ 26,40 ]…”

“…Passivation with alkali metals such as potassium have been previously shown to reduce nonradiative losses and ion migration in perovskite devices. [29][30][31][32][33][34][35][36][37][38][39][40] We prepared a series of passivated perovskite thin films by addition of different amounts of potassium iodide solution (in the range x = 0-0. 44 3 , with y = 0-1 being the fraction of bromide out of total halide (with corresponding PL emission peaks spanning 560 to 826 nm, see Figure S7, Supporting Information).…”

Enhanced Electrochemical Stability by Alkyldiammonium in Dion-Jacobson Perovskite Towards Ultrastable Light-Emitting Diodes

“…In response to the instability issue under electric eld, various strategies have been developed to improve the lifetime, while the T 50 exceeding one hundred hours is rarely reported, lagging far behind that of perovskite solar cells, which can be closely related to the higher working bias required for PeLEDs. Degradation mechanism studies demonstrate that ion migration in perovskite structure, Joule heating and instability of injection layers under electric eld are the main causes of the poor stability [13][14][15][16] . The severe ion drift in perovskite upon electric eld during operation results in the emission wavelength shift 17 , the decomposition of perovskite layer 18 , the interfacial reaction between perovskite and injection materials/electrode layers 14,19 , giving rise to a completely irreversible degradation after prolonged operation.…”