Enhanced Performance of Perovskite Light-Emitting Diodes via

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Organic Electronic Devices

Enhanced Performance of Perovskite LightEmitting Diodes via Diamine Interface Modification Lianqi Tang, Jingjing Qiu, Qi Wei, Hao Gu, Bin Du, Haiyan Du, Wei Hui, Yingdong Xia, YongHua Chen, and Wei Huang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b11866 • Publication Date (Web): 23 Jul 2019 Downloaded from pubs.acs.org on July 23, 2019

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ACS Applied Materials & Interfaces

Enhanced Performance of Perovskite Light-Emitting Diodes via Diamine Interface Modification

Lianqi Tang,† Jingjing Qiu,† Qi Wei,‡ Hao Gu,†,⊥ Bin Du,† Haiyan Du,† Wei Hui,† Yingdong Xia,†* Yonghua Chen,† and Wei Huang†,‡,§ †Key

Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM), Jiangsu National Synergistic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road, Nanjing 211816, P. R. China. ‡Shaanxi Institute of Flexible Electronics (SIFE), Northwestern Polytechnical University (NPU), 127 West Youyi Road, Xi'an 710072, China. §Key Laboratory for Organic Electronics & Information Displays (KLOEID), and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications, 9 Wenyuan Road, Nanjing 210023, China. ⊥ Institute of Applied Physics and Materials Engineering, University of Macau, Macao SAR 999078, China. Corresponding email: [email protected]

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ABSTRACT Interfacial engineering between charge transport layers and perovskite light emitting layer has been applied as an effective strategy to enhance performance of perovskite light emitting diodes (PeLEDs). Herein, we introduce a Lewis base diamine molecule (2,2-(ethylenedioxy)bis(ethylammonium), EDBE) to modify the interface between ZnMgO electron transport layer (ETL) and perovskite light emitting layer in PeLEDs. With two amino groups in EDBE, one amine can interact with beneath ZnMgO to tune the growth of perovskite films, resulting in improved electron injection and suppressed current leakage. Meanwhile, the other amine can passivate the surface trap states of the polycrystalline perovskite films, which would eliminate trap-mediated non-radiative recombination. An enhanced performance for near-infrared PeLEDs is achieved with external quantum efficiency (EQE) from 9.15% to 12.35% after incorporating EDBE interfacial layer. This work demonstrated that the introduction of Lewis base diamine molecules as ETL/perovskite interfacial agent is a promising way for high performance PeLEDs. KEYWORDS: perovskite, light-emitting diodes, interfacial engineering, diamine molecule, high efficiency

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INTRODUCTION Organometal halide perovskites have been extensively investigated as active materials in recent years for their exceptional electrical and optical properties.1-4 Due to the superior merits of excellent color purity, high photoluminescence quantum yield (PLQYs),5 balanced bipolar transmission6 and less active electronic trap states,7 organic-inorganic hybrid perovskite materials exhibit great capacity for the inexpensive fabrication of light-emitting diodes (LEDs) relative to conventional inorganic and organic LEDs.8-9 After Friend and co-workers first reported MA (CH3NH3) based perovskite LEDs (PeLEDs) at room temperature,10 great efforts have been made to improve the efficiency and stability of PeLEDs.11 In a typical PeLED, electron transport layer (ETL) and hole transport layer are usually located beside the perovskite emissive layer. The ETL exerts a great influence on electron transport and injection to the perovskite layer, and hole blocking, which acts as one of the most essential components for high performance PeLEDs. For inverted PeLEDs, the ETL is beneath the perovskite emissive layer, which is also extraordinary significant to modulate the growth of the perovskite thin film. The most commonly used ETLs in inverted PeLEDs are inorganic n-type metal oxides, such as SnO2,12 ZnO,13 and TiO2,14-15 for their large bandgaps, high electron mobility, good air stability, and high transparency for thin films in visible-infrared region.16 However, unbalanced charge injection and nonradiative charge recombination at the interface of ETL and perovskite seriously limit the efficiency of PeLEDs.17,18-19 An effective way to solve this issue is to introduce interfacial layers, such as conjugated polyelectrolytes,20 ionic liquid molecules,21 and self-assembled dipole monolayer,22 between the ETL and the perovskite layer. Lin and co-workers reported that amino acid (glycine) can act as a coupling agent to modify the interface of TiO2/CH3NH3PbI3, which is beneficial for the coverage of the CH3NH3PbI3 film and the efficient charge transfer.23 Song and co-workers24 applied amine-based interfacial molecules with multiple amino groups to modulate the energy level alignment of ZnO and the perovskite, leading to improved electron injection and device performance. For solution-processed PeLEDs, another concern is that the perovskite films tend to 3



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form defects with under-coordinated metal or halide ions at the surfaces and the grain boundaries of perovskite crystals. In this regard, it is crucial to passivate the defects of the perovskite films for high performance PeLEDs. Lewis bases have been reported as promising passivation materials. For instance, Noel et al. reported that organic Lewis bases, such as thiophene and pyridine, were effective to passivate the defects of the perovskite films, where the under-coordinated lead atoms can interact with nitrogen atoms of pyridine or sulfur atoms of thiphene.25 Likewise, Seungjin et al. demonstrated that the traps can be passivated by ethylenediamine (EDA) or polyethylenimine (PEI) treatment, leading to great improvement in efficiency and stability of PeLEDs. 26 In

this

work,

we

applied

diamine

molecules

(2,2-

(ethylenedioxy)bis(ethylammonium), EDBE) to modify the interface of ETL (ZnMgO)/perovskite emitting layer (EDBEFA3Pb4I13) for high performance PeLEDs. With two amino groups in EDBE, (ⅰ) one amino group can interact with the ZnMgO to modulate the growth of perovskite film, and ( ⅱ ) the other can passivate the perovskite defects through the coordinate bonding between lone-pair electrons from nitrogen atoms with under-coordinated lead ions from the perovskite. After the interfacial modification, high-quality perovskite films with little defect sites were obtained, and the electron injection from ZnMgO ETL to perovskite emitting layers can be also enhanced. High performance near-infrared PeLEDs were achieved with EQE surging from 9.15% to 12.35%. Our work demonstrates a promising way for developing high performance PeLEDs.

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RESULTS AND DISCUSSION Figure 1a shows the device structure of ITO/ZnMgO (20 nm)/EDBE (2 nm)/ (EDBE)FA3Pb4I13(200 nm)/TFB (35 nm)/MoO3 (8 nm)/Au (100 nm) and the working mechanism of EDBE as an interfacial layer. The emitting layer ((EDBE)FA3Pb4I13) is a quasi-2D perovskite with n=4. The ZnMgO (the atomic ratio of Zn and Mg is 43.21:12.14 (Figure S1 and Table S1), and the electron mobility of bare ZnMgO films is 1.06×10-3 cm2 V-1 s-1 (Figure S2)) act as ETL, and TFB act as hole transport layer. The EDBE is a Lewis base composed of two amino groups at the ends. After deposited between ZnMgO and perovskite, one amino group of EDBE is prone to interact with the ZnMgO to modulate the growth of perovskite thin films and to enhance electron injection from the ZnMgO ETL layer to the perovskite emitting layer.27-28 Meanwhile, another amino group of EDBE tends to coordinate bonding with under-coordinated lead ions Pb2+ of the perovskite with lone-pair electrons of the nitrogen atom, neutralizing the charges and reducing the electronic trap sites.25,29 The interaction of EDBE with ZnMgO was identified by X-ray photoelectron spectroscopy (XPS) measurement (Figure 1b). Comparing to bare ZnMgO film, N 1s peak is tracked for ZnMgO/EDBE film at a binding energy of around 400 eV. Additionally, in the high-resolution XPS spectra, we observed two asymmetric N1s peaks which are assigned to N–Zn peak (398.5 eV) and N–C peak (400.1 eV), respectively.30 These results indicate that the amino group of EDBE is bonded to the surface of ZnMgO.

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Figure 1. (a) Schematic structure of the PeLED. The insert shows working mechanism of EDBE as an interlayer; (b) XPS spectra of ZnMgO with and without EDBE modification.

Morphology of the perovskite films is one of the key factors to affect devices performance. As the perovskite film is deposited on bare ZnMgO or ZnMgO/EDBE substrate, we first evaluate the morphology of bare ZnMgO and ZnMgO/EDBE thin films. The morphology of ZnMgO/EDBE film is more compact than of bare ZnMgO (Figure 2a,b) based on scanning electron microscopy (SEM) measurements. According to the atomic force microscopy (AFM) measurements (Figure 2c,d), the root-mean-square (RMS) of the film is reduced from 1.84 nm to 1.47 nm after EDBE modification. The smoother surface can provide better interfacial contact of ZnMgO ETL with the perovskite layer, which ensures to form pinhole-free perovskite thin films with good coverage.31 As seen from SEM images (Figure 2e,f), the perovskite film deposited on the bare ZnMgO exhibits high density of pinholes as well as low 6


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coverage compared to the perovskite film with EDBE modification. The uncovered surface morphology and formation of pinholes would inevitably result in bad contacts with the ETLs and electrical shunt paths in the device. Moreover, pinholes of perovskite films would limit device performance by inducing non-radiative recombination.10,32 In contrast, the pinholes in perovskite films are reduced and dense perovskite surface morphology is obtained with deposition of EDBE on the ZnMgO. The improved perovskite morphology prepared on the ZnMgO/EDBE substrate could be due to the hydrophilic nature of EDBE. Subsequently, contact angle measurements were carried out for the surface of ZnMgO and ZnMgO/EDBE films (Figure S3). The wetting angle of ZnMgO film decreases to 22.4° with EDBE modification compared to that without EDBE treatment (33.8°), suggesting that the EDBE-modified ZnMgO substrate can provide better wetting of the perovskite precursor solution that benefits the formation of pinhole-free perovskite films by lowering the surface energy for heterogeneous nucleation.33

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Figure 2. SEM images of (a) bare ZnMgO and (b) ZnMgO/EDBE; AFM images of (c) bare ZnMgO and (d) ZnMgO/EDBE; SEM images of perovskite films on the (e) bare ZnMgO substrate and (f) EDBE/ZnMgO substrate.

The UV–visible absorption spectra of the perovskite films coated on bare ZnMgO and ZnMgO/EDBE substrates are exhibited in Figure S4. The perovskite films on different substrates display similar absorption. Nevertheless, the perovskite film on the ZnMgO/EDBE substrate reveals an appreciable enhancement in the visible region of 400-700 nm, which is related to the enhanced crystallinity of the perovskite films.34 Figure S5 shows the X-ray diffraction (XRD) measurements of the perovskite films with and without EDBE modification. The diffraction peaks at 14.07°and 28.14° are assigned to the (110) and (220) planes of (EDBE)FA3Pb4I13 perovskite crystalline 8


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structure,35-36 which indicates that the addition of the EDBE interfacial layer does not change the crystal growth direction of the perovskite films. The intensities of the peaks diffracted by α (14.07°) and δ (11.80°) phase of the (EDBE)FA3Pb4I13 on the ZnMgO/EDBE substrate are slightly boosted compared to those on the bare ZnMgO substrate, indicative of the improvements in the crystalline. This may lead to the reduced defects and thus the non-radiative recombination, which would be beneficial to the performance of PeLEDs. To investigate the impact of EDBE for defect passivation of perovskite, we carried out steady state photoluminescence (PL) spectra (Figure 3a). The PL spectra of perovskite films deposited on bare ZnMgO and ZnMgO/EDBE are measured under an excitation wavelength of 515 nm. The observed higher PL intensity is possibly due to the suppressed non-radiative recombination at the ETL/perovskite interface.37-38 These PL results confirm an overall reduction of the non-radiative recombination within the perovskite films, and are also evidence that amine-based interface layer (EDBE) may passivate trap states through coordinate bonding successfully. The effect of amino groups of EDBE on the trap passivation at the ZnMgO/perovskite interface is further confirmed by time-resolved PL (TRPL) spectra of perovskite films deposited on ZnMgO and ZnMgO/perovskite substrates, as shown in Figure 3b. The TRPL spectra displays that exciton lifetime of perovskite films with EDBE modification is longer than that without EDBE, and the τave values based on fitting with a cubic-exponential function39-40 are about 84 ns and 117 ns for the bare ZnMgO and ZnMgO/EDBE, respectively. This difference of carrier lifetimes (τave) is possibly a result of inserting an interlayer (EDBE) that can passivate defects in perovskite films and suppress non-radiative recombination. The reduction of defects could originate from the passivation effects where lone-pair electrons from nitrogen atoms of EDBE coordinate with under-coordinated Pb2+ from the perovskite. Lewis base has been reported by many research groups as an effective passivation material for perovskite films.29,41

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Figure 3. (a) PL spectra of quartz/ZnMgO/EML with and without EDBE at 515 nm excitation; (b) Time-resolved PL signal of quartz/ZnMgO/EML with and without EDBE; Kinetics of PB1, 2, 3, 4 in perovskite coated on (c) bare ZnMgO and (d) ZnMgO/EDBE; (e) Schematic of cascade carrier transfer from small-n to large-n phases. In order to interrogate charge carrier transfer from perovskite film to ZnMgO, the transient absorption (TA) spectra were carried out. Both ZnMgO/perovskite and ZnMgO/EDBE/perovskite layers are measured under 425 nm (2.91 eV) excitation (Figure S6). The TA spectra for quasi-2D (EDBE)FA3Pb4I13 perovskite (n=4) films deposited on different substrates are denoted as ZnMgO and ZnMgO/EDBE, respectively. Four distinctive photobleaching (PB) peaks are observed, which are mainly originated from the state-filling induced by photoexcited species in different 10


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dimensional perovskites and matched well with the linear absorption spectra. These PB bands of PB1 (475 nm, n = 1), PB2 (525 nm, n = 2) and PB3 (565 nm, n = 3) are assigned to the small-n value RP perovskites. While the broad signal of PB4 (760nm) closed to n =  is a result of the overlap of large-n value PB bands due to their small band differences.42 The TA kinetics of PB1, PB2, PB3 and PB4 in perovskite/ZnMgO and perovskite/EDBE/ZnMgO layers are extracted and presented in Figure 3c,d. After pumped, the initial rise of small-n value PB signals (PB1, PB2 and PB3) is identical to the laser pulse with time less than 150 fs, which corresponded to the instantaneous carrier generation in low dimensional RP perovskites. These PBs decay within time constant of 0.2-0.4 ps, where PB3 decay time is 0.26 ps for perovskite/ZnMgO layers (Figure 3c) compared to the fast decay time of 0.24 ps for perovskite/EDBE/ZnMgO layers (Figure 3d), indicating the improved energy transfer. Concurrently, the PB4 grows over time and reaches its maximum at 0.4 ps. For these sub-picosecond PB relaxations, the rapid rise of PB4 in large-n phase and the fast decay of PBs in small-n value perovskites are well matched, which represent the carrier transfer process (the carrier cascade transfer was illustrated in Figure 3e). Moreover, their rapid carrier transfer processes can compete with the defects induced exciton localization and interfacial scattering, in turn make quasi-2D perovskites are beneficial for light emission.42-43 Notably, the phenomenon of carrier transfer is also observed in the perovskite/ZnMgO layers (Figure 3c), indicates that the process of carrie transfer in perovskite QWs are barely affected by the interface layer (EDBE). The TA kinetics of PB4 peaks (760 nm) is able to be fitted very well with triple-exponential function. We also summarize the fitting results in Table S2. Then, the average lifetime (τave) of the photoexcited carriers is calculated using the following equation:44

τ ave

A1τ12 + A 2 τ 2 2 + A 3 τ32 = A1τ1 + A 2 τ 2 + A 3 τ3

(1)

The τave values of the perovskite films on bare ZnMgO and ZnMgO/EDBE substrate are calculated to be 4.83 ns and 5.30 ns, respectively. Noting that the shorter lifetime calculated from the TA kinetics than that from TRPL is ascribed to limitation of 11



measurement time window. Besides, the increased lifetime in perovskite deposited on ZnMgO/EDBE substrate can be observed, and is consistent with the results from TRPL. As aforementioned, it is consistent with the superior crystal quality and reduced defects Figure S7 shows the water contact angles in terms of different EDBE concentrations (0.5%, 1%, 1.5%, 2%). The contact angle of ZnMgO/EDBE films decreased from 23.5° to 17.6° with EDBE concentration increased from 0.5% to 2%. As the concentration of EDBE increased, more amino groups of EDBE (one end) absorbed on the surface of ZnMgO, leaving more amino groups (the other end) facing air, making ZnMgO/EDBE surface became more compatible with perovskite precursor solutions. The more hydrophilic ZnMgO/EDBE films are supposed to benefit the formation of dense and uniform perovskite films, resulting in better device performance. However, when we optimized the devices with different EDBE concentrations (0.5%, 1%, 1.5%, 2%), we found that the champion device was the one with a moderate EDBE concentration of 1% where reduced leakage current, increased radiance and EQE were observed (Figure S8a-c). Figure S8d shows a clear view of the variation of EQE and radiance with different EDBE concentrations, which were summarized in Table S3. The EQE and radiance increased until 1% EDBE concentration with a radiance of 42.70 W sr-1 m-2 and an EQE of 12.35%, and then decreased as the concentration of EDBE was further increased. It can be attributed to the insulating characteristics of EDBE that thicker EDBE films would hinder charge injection, resulting in declined device performance.[45-47] Figure 4 and Table 1 exhibit the device characteristics with and without EDBE modification in detail. Figure 4a shows the electroluminescence (EL) spectra of (EDBE)FA3Pb4I13-based devices with and without EDBE modification. The EL spectra of both devices are almost same, implying that the EDBE interlayer does not change the recombination zone. The perovskite film deposited on ZnMgO/EDBE substrate has stronger EL intensity than that on bare ZnMgO substrate, which is due to the suppressed non-radiative recombination through defects passivation in perovskite film, consisting with the PL measurements (Figure 3a). The current 12


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density-voltage-radiance (J-V-R) curves of both devices are measured (Figure 4b). After EDBE modification, the PeLED exhibited higher current density over the range of entire bias and the turn-on voltage is as low as 1.5 V (2V for the device without EDBE). The radiance of device with EDBE interlayer increases with the increasing voltage, and reaches 42.70 W sr-1 m-2 at 5.6 V. In comparison, the radiance of device without EDBE interlayer is only 14.03 W sr-1 m-2 at 5.1 V. The increased current density and lowered turn-on voltage of the EDBE-modified device demonstrate that the EDBE interlayer can effectively decrease the electron injection barrier and enhance the electron injection. Meanwhile, the reduced leakage current is also expected for effective radiative recombination of more holes and electrons, leading to enhancement of the radiance. In addition, Figure S9 shows a maximum radiance of 102.56 W sr-1 m-2 for the device with EDBE interlayer, which is higher than that of the current best near-infrared quantum dot LEDs

[48]

while lower than that of the

near-infrared organic [49] and inorganic LEDs [50] (Table S4). The open-circuit (Voc) of both devices was investigated in Figure 4c, and the values of Voc for PeLEDs with and without EDBE are 1.2 V and 0.9 V respectively. The increase of Voc indicates that the EDBE interlayer indeed reduce the electron barrier and achieve more efficient electron injection than that of the device without EDBE interlayer.51 The electron-only devices are also fabricated as ITO/ZnMgO (20 nm) with or without EDBE/ (EDBE)FA3Pb4I13 (200 nm)/PCBM (40 nm)/LiF (5 nm)/Al (100 nm). From the corresponding J-V curves (Figure 4d), we can see that the electron injection gets enhanced after introducing EDBE interlayer. The electron injection enhancement in the PeLEDs with EDBE treatment is probably due to the interface dipole originated from the electron transfer from the nitrogen of the amino groups to the zinc of ZnMgO.24 Figure 4e displays that the device with EDBE interlayer yields a high maximum EQE of 12.35% at 1.9 V compared to that of the device without EDBE (9.15% at 2.4 V), which is in consistent with the EQE vs. current density curves (Figure S10a). The PCE-current density curves are provided in Figure S10b. The peak PCE of the devices with EDBE interlayer is 10%, which is about 1.7 times higher than the control devices (5.8%). These results indicate that the EDBE interlayer 13



facilitates the efficient electron injection and suppresses exciton quenching by passivating the defect sites in perovskite films. An average EQE of 10.63% with a small relative standard deviation of 6.88% was obtained from 50 EDBE-modified devices, indicating good reproducibility of the devices (Figure 4f). The stability of the devices is also measured (Figure S11). The EQE of the devices with EDBE interlayer decreased to half of the initial value after 2.49 h under a constant current density of 10 mA cm-2, while the devices without EDBE interlayer became half of the initial value after just 0.5 h. This result confirms the introduction of EDBE interlayer is an effective way not only to enhance the device efficiency but also the device stability.

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Figure 4. Optoelectronic characteristics of PeLEDs with (orange) and without (cyan) EDBE interlayer. (a) EL spectra; (b) J-V-R curves; (c) J-Voc curves; (d) J-V curves of electron-only devices; (e) EQE-V; (f) histogram of peak EQEs measured from 50 EDBE-modified devices and 50 non-modified devices.

Table 1. Summarized performance of the PeLEDs with and without EDBE. device

Vth

Radiance

EL

EQEmax

(V)

(W sr-1 m-2)

(nm)

(%)

without EDBE

2

14.03

804

9.15

with EDBE

1.5

42.70

803

12.35

CONCLUSIONS We have demonstrated that the Lewis base diamine molecule EDBE is an effective interfacial agent to modify the interface of ETL and perovskite emitting layer in PeLEDs. With one amino group at the end of EDBE molecule, the ZnMgO/EDBE surface becomes more hydrophilic, which benefits to form dense and uniform perovskite thin films with complete coverage. In addition, the other end amino group of EDBE can passivate the defect sites of the perovskite thin films, which could eliminate trap-mediated non-radiative recombination. Accordingly, a high efficiency NIR PeLED was achieved with a maximum EQE of 12.35%, which is 35% 15



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enhancement compared to the control device (9.15%). This work indicates that the diamine interface modification is a simple and practical route to achieve high-performance PeLEDs.

EXPERIMENTAL SECTION Materials. The

EDBEI2

was

synthesized

by

adding

1

ml

of

2,2’-

(ethylenedioxy)bis(ethylamine) (EDBE, 98%, Sigma Aldrich) to 50ml of ethanol and reacted with an excess of HI solution (57 wt.% in H2O). We added the acid dropwise to the solution of amine with vigorous magnetic stirring and 0 °C for 4h. After that, the EDBEI2 precipitate was obtained by evaporating the solutions at 70 °C. Then, the precipitate was washed many times with a cold diethyl ether, and finally dried in vacuum oven at 60 °C for 12h. Formamidinium iodide (FAI, 99.5%) and lead (II) iodide (PbI2, 99.99%) were purchased from Shanghai MaterWin New Materials Co., Ltd. and TCI (Shanghai) Development Co., Ltd., respectively. Nano-ZnMgO solution (50

mg/mL,

Guangdong

Poly

OptoElectronics

Co.,

Ltd.),

Poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(4,4'-(N-(4-butylphenyl) (TFB, Xi’an Polymer Light Technology Corp.), and N,N-dimethylformamide (DMF, anhydrous, 99.7%, Sigma-Aldrich). We purchased other solvents from Sigma-Aldrich Co. LLC. Device Fabrication and Characterization. Firstly, we cleaned and dried indium tin oxide (ITO) substrates in an oven overnight. Then solutions of ZnMgO nanocrystal were deposited on the ITO-coated substrates after they were treated by UV-ozone for 15 min and annealed at 120 °C. After that, a solution of EDBE in 2-methoxyethanol (1:10 (vol. %)) was spin-coated on top of ZnMgO films at 3000 rpm. We then dried them at 120 °C under ambient atmosphere. The 25wt% perovskite precursor was prepared by dissolving EDBEI2, FAI and PbI2 with a molar ratio of 1:3:4 in DMF, followed by stirring at 60 °C for 2 h in glove-box. The perovskite emitting layer was spin-coated at 3000 rpm for 40 s and was annealed at 105 °C for 7 min in air. The substrate was cooled to room temperature, the hole transport layer of TFB was spin-coated on the surface of 16


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perovskite films from a m-xylene solution (10mg/ml) at 2000 rpm. At last, the MoOx and Au were thermally evaporated sequentially under 3 × 10-4 Pa to form the electrode. All devices were tested using a Keithley 2400 source meter and a QE65 Pro spectrometer in an N2-filled glovebox. UV-vis absorption of perovskite films can be obtained via an ultraviolet spectrophotometer (UV-1750, SHIMADZU). Hitachi F-4600 spectrofluorometer and Edinburgh FS5-TCSPC were used to acquire the PL and TRPL spectra respectively. XRD patterns were analyzed by an X-ray diffractometer (Smartlab 3 kW). SEM images and AFM images of perovskite films were characterized using JSM-7800F and Park XE-7. For TA characterization, a regeneratively amplified Yb:KGW laser at a 5 kHz repetition rate (Light Conversion, Pharos) was used to produce femtosecond laser pulses. System of DSA1005 (KRUSS GmbH) was used to measure the contact angles of ZnMgO with and without EDBE.

ASSOCIATED CONTENT Supporting Information Additional figures and tables, such as XPS spectra of ZnMgO films, electron mobility of bare ZnMgO films, water contact angles of ZnMgO films and ZnMgO/EDBE films with different EDBE concentrations, UV-vis absorption, X-ray diffraction (XRD) patterns and transient absorption (TA) spectra of perovskite films and fitting results of TA kinetics, optoelectronic characteristics of the PeLEDs with different EDBE concentrations, EQE-V-R, EQE-J, PCE-J and stability measurement of the PeLEDs, comparison of radiance of our work with the current best near-infrared (NIR) organic, quantum dot and inorganic LEDs.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]

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Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was financially supported by the National Basic Research Program of China-Fundamental Studies of Perovskite Solar Cells (2015CB932200), the National Key R&D Program of China (Grant 2017YFB1002900), the Natural Science Foundation of China (61705102, 91733302 and 51602149), Natural Science Foundation

of

Jiangsu

Province,

China

(BK20161010,

BK20161011

and

BK20150064), Jiangsu Specially-Appointed Professor program, “Six talent peaks” Project in Jiangsu Province of China and Young 1000 Talents Global Recruitment Program of China.

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