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Ultrastable near-infrared perovskite light-emitting diodes - Nature Photonics
Abstract .
Perovskite light-emitting diodes are an emerging light source technology. However, similar to perovskite solar cells, poor operational stability remains an obstacle for commercial applications. Here we demonstrate ultrastable and efficient near-infrared (~800?nm) perovskite light-emitting diodes with record-long operational lifetimes ( T 50 , extrapolated) of 11,539?h (~1.3?years) and 32,675?h (~3.7?years) for initial radiance (or current densities) of 3.7?W?sr ?1 ?m ?2 (~5.0?mA?cm ?2 ) and 2.1?W?sr ?1 ?m ?2 (~3.2?mA?cm ?2 ), respectively, with even longer lifetimes forecasted for lower radiance. Key to this stability is the introduction of a dipolar molecular stabilizer, which interacts with the cations and anions at the perovskite grain boundaries. This suppresses ion migration under electric fields, preventing the formation of lead iodide, which mediates the phase transformation and decomposition of α-FAPbI 3 perovskite. These results remove the critical concern that halide perovskite devices may be intrinsically unstable, paving the path towards industrial applications.

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Main .
Light-emitting diodes (LEDs) based on perovskite semiconductors have shown great promise as next-generation light sources, as they combine the advantages of high efficiency and spectral tunability at low processing costs 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 . Since the report of room-temperature electroluminescence (EL) from halide perovskites in 2014 (ref. 1 ), the development in the field has been fast. The external quantum efficiencies (EQEs) of perovskite light-emitting diodes (PeLEDs) exceeded the 20% milestone in 2018 (refs. 4 , 5 , 6 , 7 ), followed by recent improvements in device EQEs to over 28% (ref. 19 ).
Despite the unprecedented pace of development leading to higher device efficiencies, poor operational lifetimes of PeLEDs remain to be a critical challenge. Typically, the T 50 lifetimes (time required for the EL intensity to reach 50% of its initial value) for state-of-the-art PeLEDs under continuous operation are on the order of 10–100?h (refs. 4 , 5 , 6 , 7 , 8 , 9 , 12 , 13 , 14 , 18 , 19 , 20 ). Recent reports have shown that it is possible to achieve T 50 of 682?h at an initial radiance of 17?W?sr ?1 ?m ?2 using a dicarboxylic acid additive 21 . Practical applications demand longer operational lifetimes ( T 50 ?=?1,000–10,000?h or higher) at higher efficiencies (EQE?>?10%) for a wide range of radiance values.
Investigations into the mechanisms of PeLED degradation are still at an early stage 22 , 23 , 24 . In comparison to III–V and organic semiconductors, metal halide perovskites present some additional degradation mechanisms in device operation. The migration of ionic species under electric fields and the instability of perovskite crystal structures are some of the key issues affecting the stability of perovskite solar cells 25 , 26 , 27 , 28 , 29 , 30 and LEDs 20 , 21 , 22 , 23 , 24 . Resolving these problems to realize long device lifetimes and concurrently retaining high EL efficiencies for ideal LED operation remains a substantial challenge.
PeLED fabrication with a dipolar molecular stabilizer .
In this work, we report high-performance near-infrared PeLEDs with ultralong intrinsic operational lifetimes. The PeLEDs were prepared with a structure of glass/indium tin oxide (ITO)/polyethylenimine ethoxylated (PEIE)-modified zinc oxide (ZnO)/perovskite/poly(9,9-dioctyl-fluorene-co- n -(4-butylphenyl) diphenylamine) (TFB)/molybdenum oxide (MoO x )/gold (Au) ( Methods ) (Fig. 1a and Extended Data Fig. 1 ). The precursor solution for the perovskite emissive layer was prepared by dissolving formamidinium iodide (FAI), lead iodide (PbI 2 ) and sulfobetaine 10 (SFB10) (a dipolar molecule) at a molar ratio of 2:1: x ( x ?=?0–0.3) in N , N -dimethylformamide ( Methods ). The molecular structure of SFB10 is shown in Fig. 1b . The molar fraction of SFB10 in the precursor solution was optimized to be x ?=?0.15 (Extended Data Fig. 2 ). In this paper, samples without SFB10 are denoted as ‘control’ samples. PeLEDs with and without SFB10 show nearly identical EL spectra peaked at 803?nm (Fig. 1c (inset) and Extended Data Fig. 2a (inset)), indicating negligible effects of SFB10 on the perovskite bandgap. We choose FAPbI 3 perovskite as the base material for studying PeLED stability, as it is a compositionally simple, archetypical perovskite material suitable for both high-performance solar cells 29 , 30 and LEDs 5 , 6 , 8 .
Fig. 1: Structure and performance of PeLEDs. a , Device structure of PeLEDs. b , Molecular structure of SFB10. c , Current density–voltage curves. The inset shows the EL spectra of the control and SFB10-based PeLEDs. d , Radiance–current density characteristics. e , EQE–current density characteristics. f , η ECE –current density curves. g , Operational stability tests for SFB10-stabilized devices under 10?mA?cm ?2 . The inset shows the stability performance for the control devices. h , Accelerated aging tests for SFB10-stabilized PeLEDs at different current densities. The stability measurements were performed in a N 2 glovebox at ambient temperature (20?±?5?°C). The inset shows the ongoing stability test for an SFB10-stabilized PeLED under 5?mA?cm ?2 , showing no degradation over 3,600?h (5?months) of continuous operation. i , The T 50 lifetimes as a function of initial radiance ( R 0 ); the solid line is the fitting of the T 50 data to equation R 0 n ?×? T 50 ?=?constant, where n is the acceleration factor ( n ?=?1.86). The data points marked by the solid dots are from completed T 50 measurements (total data points, 62). The open circles are the extrapolated T 50 lifetimes for the ongoing measurements at medium and low current densities, which are expected to finish after longer times. For reference, for high-efficiency OLEDs based on tris(2-phenylpyridine)iridium(III) (Ir(ppy) 3 ), a luminance of 1,000?cd?m ?2 corresponds to a radiance of 2.1?W?sr ?1 ?m ?2 and current density of 1–2?mA?cm ?2 (refs. 41 , 43 ). A higher current density of 10?mA?cm ?2 (near the peak EQE point of the SFB10-stabilized PeLEDs) is suitable for applications requiring higher photon fluxes, and is a typical current density for accelerated aging tests for LEDs 31 , 44 , 45 .
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PeLED performance characterization .
The performance characteristics of PeLEDs with and without SFB10 are shown in Fig. 1c–f . The SFB10-based PeLEDs show peak EQEs of up to 22.8% and maximum radiance of 278.9?W?sr ?1 ?m ?2 (Fig. 1d,e ). These are substantially higher than that achieved for the control devices (peak EQE, 7.1%; maximum radiance, 158.3?W?sr ?1 ?m ?2 ). We note that the EQE values for SFB10-based PeLEDs are high (10–22.8%) across a wide range of current densities (~1 to ~500?mA?cm ?2 ) or radiance values (~0.52 to ~278?W?sr ?1 ?m ?2 ), comparing favourably with state-of-the-art near-infrared PeLEDs 5 , 6 , 8 , 20 , 21 . The PeLEDs with excellent low-, medium- and high-current-density performance show record-high energy conversion efficiencies ( η ECE , the conversion efficiency from electrical power to light) of up to 20.7% (Fig. 1f ). Compared with control devices, SFB10-based PeLEDs show considerably improved average EQEs (Extended Data Fig. 2d ). The angular emission intensity of our PeLEDs follows a Lambertian profile (Extended Data Fig. 2e ).
Device lifetime analyses with accelerated aging tests .
The operational stability tests of PeLEDs were carried out in a N 2 -filled glovebox ( Methods ). The EL intensity from SFB10-stabilized PeLEDs driven under a constant current density of 10?mA?cm ?2 (initial radiance R 0 ?=?8.1?W?sr ?1 ?m ?2 ) showed no observable degradation over 800?h of continuous operation (Fig. 1g ). In contrast, the EL intensity of the control devices rapidly reduced with a T 50 lifetime of 16.6?min under the same test conditions. To determine the operational lifetimes of SFB10-stabilized PeLEDs, accelerated aging tests were performed at a range of higher current densities (Fig. 1h ). The maximum T 50 lifetimes at current densities (or initial radiance) of 200?mA?cm ?2 (~119?W?sr ?1 ?m ?2 ), 100?mA?cm ?2 (~70?W?sr ?1 ?m ?2 ), 50?mA?cm ?2 (~39?W?sr ?1 ?m ?2 ), 20?mA?cm ?2 (~17?W?sr ?1 ?m ?2 ) and 10?mA?cm ?2 (~8.1?W?sr ?1 ?m ?2 ) were directly measured to be 22.4, 120.3, 195.3, 877.1 and 2,984?h, respectively. The average T 50 lifetimes are summarized in Table 1 . The radiance–current density relationship was determined from the averaged results of ten representative devices (Extended Data Fig. 2f ). The SFB10-stabilized PeLEDs showed excellent spectral stability under all the current densities tested (Extended Data Fig. 3 ). An empirical scaling law widely used for describing LED degradation, R 0 n ?×? T 50 ?=?constant (where n is the acceleration factor) 31 , 32 , 33 , is used for modelling the degradation behaviour of our PeLEDs. The average lifetime data at a range of radiance values can be satisfactorily fitted with this model (Fig. 1i ), revealing an acceleration factor ( n ) of 1.86. Although LED aging tests for lower current and radiance settings are still ongoing (Fig. 1h , inset), T 50 lifetimes of 11,539?h (~1.3?years), 32,675?h (~3.7?years), 6.6?×?10 5 ?h (~75?years) and 2.4?×?10 6 ?h (~2.7?centuries) can be estimated (extrapolated) for driving conditions of 5.0?mA?cm ?2 (~3.7?W?sr ?1 ?m ?2 ), 3.2?mA?cm ?2 (~2.1?W?sr ?1 ?m ?2 ), 1.1?mA?cm ?2 (~0.42?W?sr ?1 ?m ?2 ) and 0.7?mA?cm ?2 (~0.21?W?sr ?1 ?m ?2 ) , respectively (Fig. 1i and Table 1 ). To the best of our knowledge, these results represent a record for the operational stability of PeLEDs.
Table 1 Operational lifetime data for SFB10-stabilized PeLEDs Full size table
The LED lifetime tests in a N 2 atmosphere determine the intrinsic operational lifetimes that may be achieved with ideal encapsulation free from oxygen and moisture. We carried out additional accelerated aging tests for SFB10-stabilized PeLEDs in humid air (relative humidity, 70–75%) with and without simple encapsulation (standard ultraviolet (UV) resin and cover glass without desiccant) (Extended Data Fig. 4 ). Compared with PeLEDs measured in a N 2 glovebox, the encapsulated devices tested in humid air showed considerably accelerated degradation. Nevertheless, it is encouraging that at a moderate optical power flux relevant to practical applications ( R 0 ?=?2.1?W?sr ?1 ?m ?2 ), the extrapolated lifetime of the encapsulated PeLEDs in humid air reaches 10 4 ?h. The aging processes were further accelerated for unencapsulated devices in humid air. These results indicate that developing improved encapsulation for PeLEDs to achieve ultrahigh operational stability comparable to that in a N 2 atmosphere is an important future direction.
Structural and optical investigations .
To understand the origins of the high operational stability, we investigated the properties of the perovskite emissive layers. To examine the stability of the perovskite materials under elevated temperatures, which is expected to occur during device operation, we placed the perovskite samples on a hotplate set to 100?°C in a N 2 glovebox. For the control samples (Fig. 2a ), after annealing for 90?min, we observed the emergence of X-ray diffraction (XRD) peaks at around 12.6°, corresponding to the (001) diffraction peaks of PbI 2 . The diffraction peaks grew in intensity over time, indicating the continued generation of PbI 2 in the control samples. In contrast, for SFB10-stabilized perovskite samples (Fig. 2b ), no PbI 2 diffraction peaks were observed after 360?min of continuous heating. The XRD peaks at 14.0° corresponding to the (100) planes of the α-phase FAPbI 3 perovskite 29 , 30 (in agreement with the data in Extended Data Fig. 1b ) were maintained or increased in intensity during the temperature treatment, indicating excellent thermal stability under elevated temperatures.
Fig. 2: Structural and PL stability measurements of perovskite samples. a , XRD patterns of control samples after different durations of annealing at 100?°C. Here and α denote the diffraction peaks corresponding to PbI 2 and α-FAPbI 3 , respectively. b , XRD patterns of SFB10-stabilized films after different durations of annealing at 100?°C. c , XRD patterns of the control samples exposed to air (as-prepared and after 14?days). Here δ denotes the diffraction peaks corresponding to δ-FAPbI 3 . d , XRD patterns of the SFB10-stabilized samples exposed to air (as-prepared and after 322?days). e , PL intensity measurements for glass/ITO/ZnO/PEIE/perovskite samples under 400?nm pulsed laser excitation (~80?μJ?cm ?2 , 50?kHz) in air. f , PL peak wavelength measurements for glass/ITO/ZnO/PEIE/perovskite samples under 400?nm pulsed laser excitation (~80?μJ?cm ?2 , 50?kHz) in air.
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The phase stability of the perovskite samples was found to be enhanced by SFB10. For the control samples, the diffraction peak of δ-phase FAPbI 3 (11.8°) appeared after 14?days of storage in air (Fig. 2c ), accompanied by the disappearance of peaks related to the α-phase. In contrast, the SFB10-stabilized perovskite samples showed strong diffraction peaks at 14.0° (associated with the α-phase of FAPbI 3 ) without the emergence of any additional peaks (Fig. 2d ) after 322?days of storage in air, indicating excellent phase stability. Further, we examined the stability of the samples under intense pulsed laser excitation (80?μJ?cm ?2 at 50?kHz) in air. In comparison to the control samples in which the photoluminescence (PL) spectral instability may originate from the phase transition of perovskite, the SFB10-stabilized samples showed improved PL stability (Fig. 2e,f ).
Although showing different surface morphologies (Extended Data Fig. 5 ), the absorption spectra of the control and SFB10-stabilized samples exhibit similar features (Extended Data Fig. 6a ). The transient absorption (TA) spectra of the SFB10-stabilized samples are shown in Extended Data Fig. 6b,c . A ground-state bleach at 790?nm was observed, consistent with the band-to-band absorption of the FAPbI 3 perovskite. The efficiency improvement for the SFB10-stabilized PeLEDs is mainly attributed to the improved luminescence performance of the perovskite. The average photoluminescence quantum efficiency (PLQE) of the SFB10-stabilized samples was estimated to be 65?±?5%, considerably higher than that of the control samples (25?±?5%). These are in agreement with the observation that the SFB10-stabilized samples show a longer effective PL lifetime (the time required for the PL intensity to reach 1/e of the initial intensity) of 728?ns (versus 265?ns for the control samples; Extended Data Fig. 6d ), consistent with the reduced trap-filled limit voltage ( V TFL ) of electron-only devices based on the SFB10-stabilized perovskite (Extended Data Fig. 6e,f ).
Studies of chemical interactions .
Chemical interactions between the SFB10 stabilizer and perovskite precursors were studied to gain insights into the roles of the stabilizer. From the attenuated total reflectance–Fourier-transform infrared (ATR-FTIR) spectroscopy measurements (Fig. 3a ), we observed that the S=O stretching vibration peak at 1,034?cm ?1 shifted to 1,027?cm ?1 . This could be attributed to the lone electron pair donation from O of S=O to the empty orbitals of Pb 2+ . The absence of the PbI 2 XRD peak (at 12.6°) for samples prepared from mixed PbI 2 :SFB10 solution suggests the inhibition of PbI 2 crystallite formation in the presence of SFB10 (Fig. 3b and Extended Data Fig. 7 ). The formation of residual PbI 2 in the SFB10-stabilized perovskite samples may be similarly suppressed. X-ray photoelectron spectroscopy (XPS) experiments were carried out. The presence of SFB10 in the perovskite samples can be confirmed by the observation of the S2 p peaks (Extended Data Fig. 8a , consistent with the data in Extended Data Fig. 1c ). Figure 3c,d shows the XPS spectra of Pb4 f and I3 d peaks of SFB10-stabilized FAPbI 3 , pristine FAPbI 3 , SFB10-treated PbI 2 and pristine PbI 2 samples on glass/ITO/ZnO/PEIE substrates. For samples with SFB10, redshifted spectra were observed, indicating the chemical interactions between Pb 2+ and SO 3 ? in these samples. Owing to the coordination between SO 3 ? and Pb 2+ , slower crystallization rates were observed for samples with SFB10 (Extended Data Fig. 7 ), partly contributing to the improved crystalline qualities. The ratio of S/Pb on the SFB10-stabilized FAPbI 3 sample surfaces was two times higher than the molar ratio of the corresponding precursors, indicating that the majority of SFB10 was present on the surfaces of the perovskite crystals. For the control samples, the ratios of I/Pb and N(FA)/Pb on the sample surface were estimated to be 7.7:1.0 and 1.5:1.0, respectively, suggesting that the surface was iodide- and FA-rich. For SFB10-stabilized samples, the values of I/Pb and N(FA)/Pb were reduced to 4.1:1.0 and 1.4:1.0, respectively (Extended Data Fig. 8 ).
Fig. 3: Characterization of chemical interactions in SFB10-treated samples. a , ATR-FTIR spectroscopy data of the SFB10 sample and SFB10-treated PbI 2 sample (molar ratio of SFB10 to PbI 2 was 1:1). b , XRD patterns of pristine PbI 2 and SFB10-treated PbI 2 samples (molar ratio of SFB10 to PbI 2 was 1:1). Here denotes the diffraction peak corresponding to PbI 2 . c , XPS spectra of the Pb4 f peaks for SFB10-stabilized FAPbI 3 , FAPbI 3 , SFB10-treated PbI 2 and PbI 2 . d , XPS spectra of the I3 d peaks for SFB10-stabilized FAPbI 3 , FAPbI 3 , SFB10-treated PbI 2 and PbI 2 . e , 1 H NMR spectra of FAPbI 3 :SFB10 and FAPbI 3 films dissolved in DMSO-d6. The inset shows the chemical structure of FAI. f , 127 I NMR spectra of FAI:SFB10 and FAI precursors dissolved in DMSO-d6.
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To obtain more detailed information on the chemical interactions, we carried out nuclear magnetic resonance (NMR) measurements. For SFB10-stabilized perovskite samples (FAPbI 3 :SFB10), the chemical shift of 207 Pb was positioned at 652.3?ppm, strongly deviating from that of the control sample (FAPbI 3 ) at 645.1?ppm (Extended Data Fig. 9a ). This observation confirms the strong interactions between SFB10 and Pb 2+ . The chemical shift at 8.71?ppm for the FAPbI 3 control sample can be attributed to active protons on the amino groups (Fig. 3e ). For the SFB10-stabilized samples (FAPbI 3 :SFB10), the proton peak moved to 8.77?ppm, indicating the presence of hydrogen bonding between the O atoms on SFB10 and the –NH 2 group on FA + . Shifts in the SFB10 proton peaks were observed for the FAPbI 3 :SFB10 samples relative to that of neat SFB10 (Extended Data Fig. 9b,c ). The 127 I NMR spectra of the FAI and FAI:SFB10 samples were collected to examine the interactions between SFB10 and I ? (Fig. 3f ). Although the 127 I peak shifts were not significant (from 278.9 to 278.3?ppm), a clear broadening was observed for the spectral half-width (from 8.4 to 11.8?kHz). This result is consistent with the shifted and broadened I3 d spectra from the XPS data (Fig. 3d ), confirming the interactions between SFB10 and I ? .
Characterizing ion migration .
Forward and reverse current–voltage ( J – V ) scans were carried out to investigate the hysteretic behaviour of the PeLEDs (Fig. 4a,b ). Hysteresis was observed in the first scan cycle for the control devices, and the hysteretic behaviour became more pronounced with more scan cycles. In contrast, during 30?scan cycles, no observable hysteresis was recorded for the PeLEDs stabilized with SFB10. We speculate that the SFB10-stabilized devices are less affected by ion migration, as current–voltage hysteresis is known to be related to ionic transport in perovskite devices 22 , 24 , 25 , 34 , 35 , 36 . To verify this hypothesis, we carried out microscopic PL imaging 22 , 27 , 36 of the perovskite films between two in-plane Au electrodes (spacing, 100?μm), with a constant bias (3.0?V) applied across the electrodes (Fig. 4c,d ). For the control samples, a significant degradation in PL intensity occurred near the dark spots and quickly expanded across the perovskite sample over the course of the measurements (Fig. 4c and Supplementary Video 1 ). Such PL degradation behaviour for perovskite samples under external bias is evidence for ion migration 22 , 27 , 36 . In contrast, for the SFB10-stabilized samples, no significant reduction in PL intensity was observed during the measurements (Fig. 4d and Supplementary Video 2 ). These observations confirm that ion migration is effectively suppressed in SFB10-stabilized samples, in agreement with the reduced hysteresis of PeLEDs 22 .
Fig. 4: Current–voltage scans of PeLEDs and microscopic PL imaging of perovskite samples. a , Current density–voltage curves of three forward and reverse scan cycles with a scan rate of 0.05?V?s ?1 for the control PeLEDs. b , Current density–voltage curves of 30?forward and reverse scan cycles with a scan rate of 0.05?V?s ?1 for the SFB10-stabilized PeLEDs. c , Time-dependent PL images of a control sample under an external electric field (~3?×?10 4 ?V?m ?1 ) using wide-field PL imaging microscopy. Scale bars, 20??m. d , Time-dependent PL images of an SFB10-stabilized sample under an external electric field (~3?×?10 4 ?V?m ?1 ) using wide-field PL imaging microscopy. The polarity of the external electric field is marked by the ‘+’ and ‘–’ symbols. The perovskite samples were excited by a ~470 nm light source. Scale bars, 20??m.
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Discussion .
Interfacial passivation using organic molecules was found to be useful in improving the performance of PeLEDs 9 . Amongst all the organic additives, zwitterions were shown to be particularly effective in stabilizing halide perovskites for photovoltaic 26 , 28 , 37 and light-emitting 38 , 39 , 40 applications. Most of the zwitterionic molecules reported in earlier studies were found to interact with B-site metallic cations (for example, Pb 2+ and Sn 2+ ) 28 , 37 , allowing surface passivation for the perovskite materials. In this work, we have experimentally shown that the functional groups on the SFB10 stabilizer have the ability to effectively bind (or interact) with both A- and B-site cations (FA + and Pb 2+ ) and anions (I – ) at the perovskite grain boundaries (crystal surfaces) (Fig. 3 and and Extended Data Figs. 8 and 9 ), in agreement with the mechanism proposed in an earlier report on zwitterionic ligand passivation of perovskite nanocrystals 38 . Apart from passivating effects, such interactions suppress the migration of Pb 2+ and I ? ions under electric fields (Fig. 4 ), preventing the formation of lead iodide that mediates the detrimental phase transformation and decomposition of the α-FAPbI 3 perovskite (Fig. 2 ). Preliminary density functional theory (DFT) calculations (Extended Data Fig. 10a ) indicate that the O atoms on the –SO 3 group could form strong bonds with the Pb atoms on the perovskite crystal surfaces, showing a binding energy of ?0.41?eV. The strong interactions between SFB10 and FAPbI 3 perovskite are further evidenced in the differential charge density plot in Extended Data Fig. 10b , showing charge transfer between the O and Pb atoms.
Conclusions .
In summary, we have developed efficient (peak EQE, 22.8%) and ultrastable PeLEDs with record-long lifetimes ( T 50 , extrapolated) of 11,539?h (~1.3?years), 32,675?h (~3.7?years), 6.6?×?10 5 ?h (~75?years) and 2.4?×?10 6 ?h (~2.7?centuries) at initial radiance (or current densities) of 3.7?W?sr ?1 ?m ?2 (~5.0?mA?cm ?2 ), 2.1?W?sr ?1 ?m ?2 (~3.2?mA?cm ?2 ), 0.42?W?sr ?1 ?m ?2 (~1.1?mA?cm ?2 ) and 0.21?W?sr ?1 ?m ?2 (~0.7?mA?cm ?2 ), respectively. The PeLEDs driven at 5?mA?cm ?2 (3.7?W?sr ?1 ?m ?2 ) have shown no EL degradation over 3,600?h (5?months) of continuous operation. Key to this breakthrough is the introduction of a dipolar stabilizer, SFB10, in the preparation of the perovskite emissive layers. Beside serving as an agent for trap passivation for efficient LED operation (EQEs of 10–22.8%) for a wide range of current densities (~1 to ~500?mA?cm ?2 ), we have shown that the stabilizer effectively interacts with both A- and B-site cations (FA + and Pb 2+ ) and anions (I – ) at the FAPbI 3 perovskite grain boundaries. Such interactions suppress the migration of ions under electric fields, preventing the formation of lead iodide, which mediates the detrimental phase transformation and decomposition of the α-FAPbI 3 perovskite. The device lifetime results satisfy the stability requirement ( T 50 ?>?10,000?h at R 0 ?≈?0.21–2.1?W?sr ?1 ?m ?2 ) for commercial organic LEDs (OLEDs) 32 , 41 , 42 , eliminating the critical concern that halide perovskite devices might be intrinsically unstable. The ultralong device lifespans showcase the strong potential of next-generation light-emitting technologies based on perovskite semiconductors.
Methods .
Preparation of perovskite precursor solution .
The perovskite precursor solution was prepared by dissolving FAI (99.99%, TCI), PbI 2 (99.99%, TCI) and SFB10 (98%, Sigma-Aldrich) at a molar ratio of FAI:PbI 2 :SFB10?=?2:1: x in N , N -dimethylformamide (anhydrous, 99.80%, Sigma-Aldrich). The concentration of PbI 2 was 0.13?M. The precursor solution was filtered through 0.22?μm filters before use.
Fabrication of PeLEDs .
ITO glass substrates were sequentially cleaned with deionized water, isopropanol and acetone in an ultrasonic bath for 15?min. Before spin coating, the substrates were treated by UV–ozone for 60?min. The ZnO layers were deposited in air by spin coating the ZnO nanoparticle solution 46 at 5,000?rpm for 60?s, followed by annealing at 150?°C for 10?min. PEIE in isopropanol (0.04?wt%) was then spin coated on ZnO at 5,000?rpm for 60?s, followed by annealing at 100?°C for 10?min. Subsequently, the substrates were transferred into a N 2 -filled glovebox. The perovskite films were spin coated from the precursor solution at 5,000?rpm for 90?s, followed by annealing at 100?°C for 10?min. Then, 100?μl chlorobenzene was drop casted (within 1?s) onto the sample at ~5?s after the start of the spin-coating process. Then, a TFB layer was deposited from the chlorobenzene solution (12?mg?ml ?1 ) at 4,000?rpm. Finally, MoO x (~15?nm) and Au (60?nm) were sequentially deposited using a thermal evaporation system through a shadow mask under a base pressure of 4?×?10 ?4 ?Pa. The active pixel area of the devices is 5.25?mm 2 .
Characterization of PeLED performance .
The current density–voltage–radiance ( J – V – R ) characteristics of the PeLEDs were measured using a Keithley 2400 sourcemeter unit and a calibrated commercial LED performance analysis system (EVERFINE OLED-200). The EQE measurement setup was cross-calibrated against a standard integrating sphere coupled with an Ocean Optics QE-Pro spectrometer, and with a silicon photodetector. The J – V characteristics of the devices were scanned from zero bias to forward bias at a rate of 0.1?V?s ?1 . The stability measurements were performed in a N 2 glovebox at ambient temperature (20?±?5?°C) using a multichannel LED lifetime-testing system (Crysco). The concentrations of water and oxygen in the glovebox were maintained to be <0.1?ppm. To allow accurate analyses, the lifetimes for the ongoing tests at lower current densities were estimated based on 62?data points directly obtained from completed T 50 tests in the range of higher current densities (10–200?mA?cm –2 ). The accelerated aging experiments at high current densities were limited to a maximum current density of 200?mA?cm ?2 , beyond which the photodetectors in the LED lifetime tester were saturated due to the very high photon fluxes from the PeLEDs. In comparison, accelerated aging tests for OLEDs and quantum-dot LEDs were typically performed at current densities of <100?mA?cm ?2 in previous studies 31 , 32 . For measurements in humid air (relative humidity, 70–75%), the devices were encapsulated with UV epoxy (NOA81, Norland Products)/cover glass before tests. The angular EL intensity profile was recorded using an Ocean Optics Maya2000 Pro spectrometer.
STEM measurements .
Spherical aberration-corrected scanning transmission electron microscopy (STEM) (FEI, Titan ChemiSTEM) measurements were used for collecting the cross-sectional images of devices and the energy-dispersive spectroscopy mapping data of the perovskite films. The samples for high-angle annular dark field–STEM measurements were prepared using a dual-beam focused-ion-beam system (Quanta 3D FEG). The measurements were carried out on the same day as the sample preparation.
XRD measurements .
The XRD patterns of the samples were collected by an X-ray diffractometer (Shimadzu XRD 7000) using Cu Kα 1,2 radiation (wavelength λ ?=?1.541??). The measurements were performed under the continuous mode within a scan range of 5°? Steady-state PL and PL stability measurements .
The steady-state PL spectra of the films were collected using an Ocean Optics QE-Pro spectrometer; a 405?nm continuous-wave laser was used to excite the perovskite films. The PL stability experiments were performed by exciting the samples in air using a 400?nm femtosecond laser (pulse width, ~270?fs); the PL data from the samples were collected using an Ocean Optics Maya2000 Pro spectrometer.
SEM measurements .
Scanning electron microscopy (SEM) measurements were carried out on perovskite films deposited on glass/ITO/ZnO/PEIE. The SEM images of the films were recorded by a field-emission scanning electron microscope (Zeiss Ultra 55 SEM).
Atomic force microscopy measurements .
The atomic force microscopy tests were conducted under the tapping mode (Veeco MultiMode).
UV–Visible absorption measurements .
A double-beam spectrophotometer (Aoyan UV1901PC) was used to collect the UV–Visible absorption spectra.
Femtosecond TA spectroscopy .
The femtosecond TA experiments were carried out using a Yb:KGW femtosecond laser (PHAROS, Light Conversion; 1,030?nm, ~270?fs, 200?μJ per pulse and 50?kHz) and a Femto-TA100 spectrometer (Time-Tech Spectra). Briefly, the 1,030?nm output pulse from the laser was split into two parts with a 90/10 beamsplitter. The reflected part was used to pump an ORPHEUS?F optical parametric amplifier to generate a wavelength-tunable laser pulse from 320?nm to 2?μm as the pump beam. The transmitted part was split again into two parts. One part with ~30% was attenuated with a neutral-density filter and focused into a 1-cm-thick YAG crystal to generate a white-light continuum used for the probe beam. The probe beam was focused with an Ag parabolic reflector onto the sample. After passing through the sample, the probe beam was collimated and then focused into a fibre-coupled spectrometer with complementary metal–oxide–semiconductor sensors and detected at a frequency of 10?kHz. The intensity of the pump pulse was controlled by a tunable neutral-density filter wheel. The delay between the pump and probe pulses was controlled by a motorized delay stage. The pump pulses were chopped by a synchronized chopper at 5?kHz. For TA measurements, the perovskite films were sealed in a N 2 -filled chamber with a pair of quartz windows for light propagation.
TCSPC measurements .
Time-correlated single-photon counting (TCSPC) measurements were used to determine the PL lifetimes of the samples. The excitation laser was generated from the same laser source used in the TA measurements. A 400?nm laser excitation beam was focused onto the perovskite samples, and the PL was collected by an object and detected after a long-pass filter (FELH450, Thorlabs) by a fibre-coupled avalanche photodiode (APD; ID100, IDQ). A PicoHarp 300 counter (PicoQuant) was used to obtain the time-resolved decay curves. The excitation energy density was attenuated to 20?nJ?cm ?2 using a tunable neutral-density filter. For the TCSPC measurements, the perovskite films were sealed in a N 2 -filled chamber with a pair of quartz windows.
FTIR measurements .
FTIR spectroscopy (Thermo Scientific, Nicolet iS10) was used under the attenuated total reflectance mode. The FTIR spectra were collected in the range of 4,000 to 400?cm ?1 at a resolution of 0.4?cm ?1 and a scan number of 64.
XPS measurements .
The XPS spectra were obtained using a Thermo Scientific ESCALAB 250Xi spectrometer with an Al Kα radiation source (1,486.6?eV). The atomic ratios for determining the material compositions on the sample surfaces were calculated using a widely employed method 47 .
NMR measurements .
High-resolution NMR measurements were carried out using an Agilent DD2 600?MHz NMR spectrometer. Samples for 1 H NMR measurements: perovskite films and SFB10 powder (40?mg) dissolved in 0.6?ml dimethyl sulfoxide-d 6 (DMSO-d6). Samples for 127 I NMR measurements (at Larmor frequencies ν ( 127 I)?=?120.111?MHz): FAI (44.7?mg) and FAI:SFB10 (44.7:40.0?mg) dissolved in 0.6?ml DMSO-d6. Samples for 207 Pb NMR measurements: FAI:PbI 2 (44.7:59.9?mg) and FAI:PbI 2 :SFB10 (44.7:59.9:12.0?mg) dissolved in 0.6?ml DMSO-d6.
PL imaging microscopy experiments .
The devices were prepared by depositing gold electrodes (spacing between electrodes, 100?μm) on the perovskite films, followed by spin coating of a poly(methyl methacrylate) (20?mg?ml ?1 in butyl acetate) capping layer (to isolate the samples from the ambience). Butyl acetate is a poor solvent for the FAPbI 3 perovskite, and it has limited impact on the quality of the films (Supplementary Fig. 1 ). The custom-built measurement setup was based on a commercial microscope (FN1, Nikon). The perovskite films were excited by an internal illuminator with a filter, providing optical excitation at a central wavelength of ? 470?nm. The PL signal was filtered to remove the residual excitation before being directed onto a high-speed charge-coupled device camera (pco.pixelfly, PCO). A constant bias of 3?V was supplied across the electrodes through a Keithley 2612B sourcemeter unit. The average electric field strength is expected to be much greater in working PeLEDs considering the thickness of the device’ functional-layer stack (<1?μm) between the electrodes. Despite this limitation, it has been shown that the PL imaging experiments in the lateral configuration is a useful tool for the assessment of ion migration relevant to the stability of perovskite devices 22 , 27 , 45 .
DFT calculations .
DFT calculations with Perdew–Burke–Ernzerhof exchange–correlation functional were performed to understand the mechanism of the stabilization of the FAPbI 3 crystal surfaces with SFB10 molecules, using the Vienna ab initio simulation package 48 . The outermost electrons were treated as valence electrons whose interactions with the remaining ions were modelled by pseudopotentials generated within the projector augmented wave method 49 . The structural optimization calculation for FAPbI 3 bulk was taken, with an energy cutoff of 400?eV and force convergence of <0.02?eV?? ?1 . During the optimization, the positions of the atoms and the shape and volume of the unit cell were allowed to relax. The gamma-centred scheme was used for sampling the Brillouin zone, with an 8?×?8?×?8 k -point mesh. The bulk lattice constants were then calculated to be a ?=?6.480??, b ?=?6.300?? and c ?=?6.398??, which agree well with a previous report 50 . A slab model was built to calculate the surface adsorption of SFB10 molecules on a FAPbI 3 crystal surface, the Pb–I-terminated FAPbI 3 perovskite (001) surface was cleaved in the size of 3.0?units?×?1.0?unit?×?2.5?units with a 20?? vacuum layer and the I–FA-terminated bottom layer was fixed. An energy cutoff of 400?eV and 1?×?4?×?1 gamma-centred k -point meshes were used to achieve force convergence of <0.05?eV?? ?1 for all the molecules and surfaces. The differential charge density was calculated as Δ ρ ?=? ρ system ?–? ρ surface ?–? ρ molecule .
Data availability .
The main data supporting the findings of this study are available within the Article and its Supplementary Information . Extra data are available from the corresponding authors upon reasonable request.
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Acknowledgements .
This work was supported by the National Key R&D Program of China (grant no. 2018YFB2200401) (D.D.), the National Natural Science Foundation of China (NSFC) (61975180 (D.D.), 62005243 (B.Z.), 62005230 (M.C.), 61974126 and 51902273 (C.L.) and 52102177 (W.L.)), Kun-Peng Programme of Zhejiang Province (D.D.), Natural Science Foundation of Zhejiang Province (LR21F050003) (B.Z.), Natural Science Foundation of Fujian Province (2021J06009) (C.L.), Natural Science Foundation of Jiangsu Province (BK20210313) (W.L.), Top-Notch Academic Programs Project of Jiangsu Higher Education Institutions (TAPP) (W.L.), Jiangsu Specially-Appointed Professor Program (W.L.), Fundamental Research Funds for the Central Universities (2020QNA5002 (B.Z.), 2021FZZX001–08 (Z.H.), and 20720200086 and 20720210088 (M.C.)) and Zhejiang University Education Foundation Global Partnership Fund (D.D.). We are grateful to M. Yu and Y. Zhao for their administrative support. We acknowledge the technical support from the Core Facilities, State Key Laboratory of Modern Optical Instrumentation, Zhejiang University. This work was supported by the College of Optical Science and Engineering (Zhejiang University), which celebrates its 70th anniversary in 2022.
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Authors and Affiliations .
State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering; International Research Center for Advanced Photonics, Zhejiang University, Hangzhou, China
Bingbing Guo,?Runchen Lai,?Zhixiang Ren,?Yaxiao Lian,?Xuhui Cao,?Shiyu Xing,?Yaxin Wang,?Chen Zou,?Baodan Zhao?&?Dawei Di
School of Electronic Science and Engineering, Xiamen University, Xiamen, China
Sijie Jiang,?Puyang Li,?Mengyu Chen?&?Cheng Li
Future Display Institute of Xiamen, Xiamen, China
Sijie Jiang,?Puyang Li,?Mengyu Chen?&?Cheng Li
Lab of Dielectric Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou, China
Linming Zhou?&?Zijian Hong
MIIT Key Laboratory of Aerospace Information Materials and Physics, College of Physics, Nanjing University of Aeronautics and Astronautics, Nanjing, China
Weiwei Li
Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK
Weiwei Li
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Contributions .
B.G. planned the experiments under the guidance of D.D. and B.Z. B.G. designed and fabricated the highly stable and efficient PeLEDs and carried out the device characterization and data analyses. B.G. and R.L. performed the TCSPC measurements. R.L. performed the TA experiments. S.J. and P.L. conducted the microscopic luminescence imaging experiments under the supervision of C.L. and M.C. Z.R. assisted with the preparation of samples and experimental setups for the device stability tests. L.Z. carried out the DFT calculations under Z.H.’s supervision. X.C. and B.G. performed the angular-emission profile measurements. B.G., B.Z. and D.D. wrote the initial manuscript, with useful inputs from Y.L. All the authors contributed to the work and commented on the paper.
Corresponding authors .
Correspondence to Baodan Zhao or Dawei Di .
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Competing interests .
D.D., B.G., Y.L. and B.Z. are inventors on CN patent application no. 202111447766.0. The remaining authors declare no competing interests.
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Extended data .
Extended Data Fig. 1 HAADF-STEM images and EDS composite mapping of SFB10-based perovskite devices. .
a , Cross-sectional HAADF-STEM image of a SFB10-stabilized device. Scale bar: 100?nm. b , Cross-sectional HAADF-STEM image of a SFB10-stabilized sample. Scale bar: 2?nm. The lattice spacings (10 fringes) show agreement with the cubic α-phase of FAPbI 3 . c , EDS elemental maps of the SFB10-stabilized perovskite device. Scale bar: 50?nm.
Extended Data Fig. 2 Further performance data of control and SFB10-based PeLEDs. .
a , Current density-voltage characteristics. Inset shows the EL spectra of PeLEDs with different SFB10 content. b , Radiance-voltage characteristics. c , EQE-current density characteristics. d , EQE histograms for control and SFB10-based PeLEDs. e , Angular emission profile of SFB10-based PeLEDs. f , The radiance-current density relationship determined from the averaged results of 10 representative devices.
Extended Data Fig. 3 Spectral stability measurements of SFB10-stabilized PeLEDs. .
a , EL spectrum of a SFB10-stabilized device measured after 2000 h aging under 10?mA?cm ?2 . b , EL spectrum of a SFB10-stabilized device measured after 450?h aging under 20?mA?cm ?2 . c , EL spectrum of a SFB10-stabilized device measured after 114?h aging under 50?mA?cm ?2 . d , EL spectrum of a SFB10-stabilized device measured after 68?h aging under 100?mA?cm ?2 . e , EL spectrum of a SFB10-stabilized device measured after 22.4?h aging under 200?mA?cm ?2 . f , EL spectra of SFB10-stabilized PeLEDs before and after aging tests.
Extended Data Fig. 4 Accelerated aging tests in humid air (70–75% RH, 20?±?5 °C) for SFB10-stabilized PeLEDs with and without encapsulation. .
a , Accelerated aging tests for encapsulated devices at different current densities. b , Accelerated aging tests for unencapsulated devices at different current densities. c , The T 50 lifetimes as a function of initial radiance (R 0 ) for encapsulated devices, the dash line is the fitting of T 50 data to equation R 0 n × T 50 ?=?constant, where n is the acceleration factor (n?=?2.10). d , The T 50 lifetimes as a function of initial radiance (R 0 ) for unencapsulated devices. The acceleration factor (n) is 1.89.
Extended Data Fig. 5 Morphological characterization for control and SFB10-stabilized samples. .
a , SEM image of the control samples. Scale bar: 500?nm. b , SEM image of SFB10-stabilized samples. Scale bar: 500?nm. c , AFM image of the control samples. Scale bar: 1?μm. d , AFM image of SFB10-stabilized samples. Scale bar: 1?μm.
Extended Data Fig. 6 Additional optical and electrical characterizations for control and SFB10-stabilized samples. .
a , Absorbance and PL spectra of the perovskite films. b , Transient absorption (TA) spectra of a SFB10-stabilized sample. c , The TA dynamics probed at 790?nm. d , PL decay curves of the perovskite films (excitation fluence: 20 nJ cm ?2 ). e , The current-voltage characteristics of an electron-only device based on the control sample. f , The current-voltage characteristics of an electron-only device based on SFB10-stabilized perovskite. The device structure was glass/ITO/ZnO/PEIE/perovskite/TPBi/LiF/Al.
Extended Data Fig. 7 Additional optical measurements and sample appearance of SFB10-stabilized FAPbI 3 , pristine FAPbI 3 , SFB10-treated PbI 2 , and pristine PbI 2 . .
a , Absorption spectra of PbI 2 and PbI 2 :SFB10 samples. The molar ratio of SFB10 to PbI 2 was 1:1. Inset: photos of pristine PbI 2 and SFB10-treated PbI 2 samples after annealing. b , PL spectra of control and SFB10-stabilized samples before annealing. Inset: photos of control and SFB10-stabilized perovskite samples before annealing.
Extended Data Fig. 8 XPS measurements of SFB10-stabilized FAPbI 3 , pristine FAPbI 3 , SFB10-treated PbI 2 , and pristine PbI 2 . .
a , S 2p ; b , N 1s ; c , O 1s ; d , C 1s spectra of samples for SFB10-stabilized FAPbI 3 , pristine FAPbI 3 , SFB10-treared PbI 2 and pristine PbI 2 . The XPS spectra were calibrated with C 1s peak at 284.8?eV. e , The atomic ratio of I/Pb on the surfaces of the control and SFB10-stabilized perovskite samples. f , The atomic ratio of N(FA)/Pb on the surfaces of the control and SFB10-stabilized perovskite samples.
Extended Data Fig. 9 Additional liquid-state NMR characterization. .
a , 207 Pb NMR spectra of FAPbI 3 : SFB10 and FAPbI 3 precursors dissolved in DMSO-d6. b - c , 1 H NMR spectra of FAPbI 3 : SFB10 films and SFB10 dissolved in DMSO-d6.
Extended Data Fig. 10 DFT analyses. .
a , Surface configuration after relaxation. The SFB10 molecule tends to lie on the surface with a -SO 3 group close to the Pb atom. The long carbon chain of SFB10 extends along the perovskite crystal surface. The chemical bonding between Pb and O can be observed with a binding energy of ?0.41?eV. b , Differential charge density plot (isosurface value of 0.0015 e/?; charge accumulation/depletion is plotted in yellow/cyan) for the equilibrium structure, showing that the bonding between the O and Pb atoms also induces charge redistribution on the -SO 3 group, Pb atom and partially along the carbon chain, further confirming the strong chemical interactions between the SFB10 molecule and FAPbI 3 crystal surfaces. The long carbon chain of SFB10 extends along the perovskite crystal surface. This could enhance the surface stability and increase the barrier to ion migration perpendicular to the perovskite crystal surface.
Supplementary information .
Supplementary Information .
Supplementary Fig. 1.
Supplementary Video 1 .
Time-dependent PL imaging of a control sample under an external electric field (~3?×?10 4 ?V?m ?1 ).
Supplementary Video 2 .
Time-dependent PL imaging of an SFB10-stabilized sample under an external electric field (~3?×?10 4 ?V?m ?1 ).
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Guo, B., Lai, R., Jiang, S. et al. Ultrastable near-infrared perovskite light-emitting diodes. Nat. Photon. (2022). https://doi.org/10.1038/s41566-022-01046-3
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Received : 03 November 2021
Accepted : 23 June 2022
Published : 08 August 2022
DOI : https://doi.org/10.1038/s41566-022-01046-3
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