Suppressing Ion Migration Enables Stable Perovskite Light‐Emitting Diodes with All‐Inorganic Strategy

Abstract

2001834 (1 of 8) mobility, and low cost, make this emergent technology very promising. [1-9] Recently, near-infrared and green PeLEDs with external quantum efficiency (EQE) over 20% were reported, [10-13] signifying that we are one step closer to the practical application of PeLEDs in lighting and displays. Several metrics are generally used to assess the performance of PeLEDs. EQE and lifetime are of particular importance among them. Besides, brightness is an intuitive criterion for visible LEDs. [14-16] Most of the previous studies have not yet matched these three metrics simultaneously. For example, the green PeLED with the to-date record-high EQE of 20.3%, the record of PeLEDs so far, had a maximal luminance of 14 000 cd m −2 and 46 h lifetime (measured at continual mode of 100 cd m −2); [11] while for the most stable green PeLED to date (lifetime 250 h measured at initial brightness of 100 cd m −2), the EQE and luminance were 10.5% and 16 436 cd m −2 , respectively. [17] Critical factors that affect the PeLEDs lifetime include the materials stability, the intrinsic defects in perovskites, and most importantly, ion migration within devices. [18-21] Stable perovskites with high luminescence are essential to achieve PeLEDs with both high stability and efficiency. Hybrid organicinorganic perovskites degrade quickly against the heat and environmental moisture. All-inorganic perovskites usually have higher stability, but their PLQY is generally unsatisfactory because of the relatively low film quality. [22] The nonuniform morphology of perovskite films and the high density of defect states are detrimental to the electroluminescence (EL) emission. Intrinsic defects can mediate charge-carrier trapping thus leading to nonradiative recombination loss, which is harmful to the device performance. For efficient PeLEDs with high stability, many efforts have been devoted to reduce the trap states in perovskite films. Introducing large organic ligands is a widely adopted approach, as it can passivate defects and achieve a relatively high film quality by stabilizing the perovskite surfaces or facilitating the formation of low-dimensional perovskites. [13,23-27] Through optimal composition and phase engineering, Yang et al. achieved an EQE of 14.36% and an improved stability for green PeLEDs with quasi-2D perovskites. [27] Meanwhile, Xu et al. demonstrated a highly efficient and stable PeLEDs through the rational design of passivation molecules. [13] The improved stability results from a combination of reduced Joule heating caused by the high efficiency and the suppression of ion migration due to reduced defect density.

Recent Progress on Perovskite Surfaces and Interfaces in Optoelectronic Devices

“…[ 201 ] With benzylamine‐based surface treatments, the PeLEDs with formamidinium lead iodide films (near‐infrared emission) make more efficient than those of the OLEDs and QDLEDs and delivers the L 50 at 100 mA cm 2 that is as high as ≈24 h. [ 202 ] Through the introduction of a PMMA layer between the perovskite and the electron transport layer, ensuring charge‐carrier (electrons and holes) balance across the whole PeLED that has led to the L 50 at 100 cd m −2 to be about 100 h for green PeLEDs (also the realization of EQEs >20% in green emission). [ 6 ] By the use of ZnS/ZnSe cascade electron transport layers, the electric‐field‐induced ion migration for the PeLEDs can be suppressed, resulting in the L 50 at an initial luminance of 120 cd m −2 to be 255 h. [ 203 ] Similarly, based on all‐inorganic interface materials and the fine control of the band alignment, all factors associating with charge carrier injection, transport, and radiative recombination have been synergistically managed, [ 204 ] showing improved L 50 of ≈450 h (with an initial brightness 1000 cd m −2 ). [ 205 ] By mitigating halide segregation on the perovskite surface with the removal of mixed halides, the resulting deep‐blue emission PeLEDs can operate in a continuous current mode, producing a record L 50 of ≈108 h for deep‐blue PeLEDs.…”

Understanding the Synergistic Effect of Device Architecture Design toward Efficient Perovskite Light‐Emitting Diodes Using Interfacial Layer Engineering

“…Thin LiF interlayers are used for insulating layers as described above, and additionally inorganic ZnS and ZnSe are deposited for ETL instead of organic ETL electron transport materials (Figure 11b). [ 143 ] The device exhibited extremely long half‐lifetime of 255 h at 120 cd m −2 , L max of 156 155 cd m −2 , and EQE max of 11.05% (Figure 11c). [ 143 ] The reason for the long device lifetime is confirmed by elemental analysis.…”

“…[ 143 ] The device exhibited extremely long half‐lifetime of 255 h at 120 cd m −2 , L max of 156 155 cd m −2 , and EQE max of 11.05% (Figure 11c). [ 143 ] The reason for the long device lifetime is confirmed by elemental analysis. The inorganic ETL and IPI structured device retained the elements of MHP after 50 min operation, while a large number of elements of MHP were diffused through interlayers in the conventional structured device.…”

“…The inorganic ETL and IPI structured device retained the elements of MHP after 50 min operation, while a large number of elements of MHP were diffused through interlayers in the conventional structured device. [ 143 ] Compact inorganic ETLs and insulating LiF interlayers can sufficiently block the ion migration. [ 143 ]…”

“…[ 143 ] Compact inorganic ETLs and insulating LiF interlayers can sufficiently block the ion migration. [ 143 ]…”