High-Efficiency Red Light-Emitting Diodes Based on Multiple Quantum

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Letter

High-efficiency Red Light-emitting Diodes Based on Multiple Quantum Wells of Phenylbutylammonium-cesium Lead Iodide Perovskites Zhuofei He, Yang Liu, Zhaoliang Yang, Jing Li, Jieyuan Cui, Dong Chen, Zhishan Fang, Haiping He, Zhizhen Ye, Haiming Zhu, Nana Wang, Jianpu Wang, and Yizheng Jin ACS Photonics, Just Accepted Manuscript • Publication Date (Web): 13 Feb 2019 Downloaded from http://pubs.acs.org on February 13, 2019

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High-efficiency Red Light-emitting Diodes Based on Multiple Quantum Wells of Phenylbutylammonium-cesium Lead Iodide Perovskites Zhuofei He,§# Yang Liu,†# Zhaoliang Yang, ⊥ # Jing Li,┘ Jieyuan Cui,§ Dong Chen,§ Zhishan Fang,┘ Haiping He,* ┘ Zhizhen Ye, *┘ Haiming Zhu, ⊥ Nana Wang,┐ Jianpu Wang,┐ and Yizheng Jin*§

#These

authors contributed to this work equally.

§Centre

for Chemistry of High-Performance & Novel Materials, State Key

Laboratory of Silicon Materials, Department of Chemistry, [email protected], †State

Key Laboratory of Silicon Materials, Centre for Chemistry of High-Performance

& Novel Materials, School of Materials Science and Engineering,

⊥

Centre for

Chemistry of High-Performance & Novel Materials, Department of Chemistry, ┘State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China, [email protected], [email protected] ┐Key

Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials

(IAM), Jiangsu National Synergetic Innovation Centre for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road, Nanjing 211816, China

KEYWORDS: perovskites; recombination channel; multiple quantum wells (MQWs); light-emitting diodes (LEDs);

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Abstract

Inorganic-organic hybrid perovskites have drawn considerable attention in photovoltaics and light-emitting diodes (LEDs) due to their exceptional optoelectronic properties. Perovskite multiple quantum wells (MQWs), which employ large organic ammonium cations to form layered structures, have been developed for high-efficiency perovksite LEDs (PeLEDs). However, little is known about the impacts of large organic ammonium cations on the properties of MQW films. In this work, we report MQW perovskites of phenylbutylammonium-caesium lead iodides, which exhibit a photoluminescence peak at 664 nm with a quantum efficiency of 58%. These perovskite MQW films enable red LEDs with high external quantum efficiencies (EQEs) of up to 13.3%. Furthermore, we deposit MQW perovskites of butylammonium-caesium lead iodides. The comparisons of the two perovskite MQW films demonstrate that the choices of large organic ammonium cations significantly influence the properties of the perovskite MQW films, i.e., distributions of the quantum-well thicknesses, energy transfer processes and recombination channels of the emissive centers. Our study shall shed light on rational design of high-performance perovskite MQW films towards their potential application as red light sources.

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Light-emitting diodes (LEDs) based on solution-processed thin films of lead halide perovskites have attracted considerable research interest because of their potential applications in large-area displays and solid-state lighting.1-5 Recent studies show that perovskite films with self-organized multiple-quantum-well (MQW) structures can serve as an appealing system to achieve high-efficiency LEDs.6-20 The MQW films are a mixture of layered Ruddlesden−Popper perovskites with a general formula of L2Sn1PbnX3n+1,

where L, S, X, and n represent large cations with long-chain ammonium

groups, small methylammonium (or cesium) cations, halide ions (I− or Br−), and the number of PbX4 octahedral layers within a crystallite, respectively.21,22 In analogy to the inorganic quantum wells, these Ruddlesden−Popper perovskites with different n values (thicknesses) exhibit size-dependent band gaps.23 Fast energy funnelling from QWs with larger band gaps (smaller n values) to QWs with smaller band gaps (larger n values) can occur, leading to efficient radiative recombination.6,7,24 The MQW perovskite films generally show smooth surface morphologies. Furthermore, MQW perovskite films can be in-situ grown by facile solution-based methods. The unique combination of these attractive properties of MQW perovskite films has led to a few high-efficiency LEDs. For example, external quantum efficiency (EQE) of green and near infra-red MQW PeLEDs has reached 15.5% and 17.6%, respectively.25,26 Despite the encouraging progresses of the MQW PeLEDs, several challenges remain to be addressed. Given the efficient energy funnelling processes, the emission spectra of perovskite MQW films are largely determined by the properties of thicker QWs with narrower band gaps. Similar to colloidal nanocrystals, the optical properties of these emissive centers are largely determined by passivation ligands, i.e., the L cations.27,28 However, little is known about the impacts of L cations on the structures and optical properties of MQW films. Besides, the emission peaks of most red PeLEDs based on MQWs are in the range of 680 to 800 nm.9,29-32 According to the photopic luminosity function, such electroluminescence spectra of the red PeLEDs deteriorate their luminance efficiency.33 For red MQW PeLEDs with emission peak below 680 nm, the highest reported EQE is 7.3%12, which is inferior to their green and infra-red counterparts.25,26 3


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Here we use all-iodide perovskite MQW films to achieve red PeLEDs with emission spectra below 680 nm. We find that the emission spectra of the perovskite MQW films are readily tuned by controlling the ratio of large ammonium L cations in the precursor solution. A focus of our study is to reveal how the choices of the L cations influence the properties of red perovskite MQW films and thereby, the efficiency of red PeLEDs. We use phenylbutylammonium (PBA) as the L cations to deposit red L2Csn−1PbnI3n+1 MQW films. A typical perovskite film of PBA2Csn−1PbnI3n+1 (see Fig. 1a for the schematic structure) is deposited onto a poly(9-vinlycarbazole) (PVK) film from a precursor solution of PBAI (0.11 mmol), CsI (0.12 mmol) and PbI2 (0.13 mmol) dissolved in 1 ml (DMSO). For the sake of clarity, this film is abbreviated as PBA0.83PI, where 0.83 refers to the molar ratio of PBAI: PbI2 in the precursor solution. Atomic force microscopy (AFM) measurements (Fig. 1b) show that the PBA0.83PI film possesses a smooth and uniform surface coverage with a low root-mean-square roughness of 1.3 nm. Absorption spectrum of the PBA0.83PI film (Fig. 1c) shows two excitonic peaks at 551 nm and 587 nm, which can be assigned as the CsPbI3 QWs with n = 2 and 3, respectively.16,34 In the absorption spectrum, optical features corresponding to QWs with larger n values are not clear. Photoluminescence (PL) spectrum of the PBA0.83PI film shows one dominant peak at 661 nm (1.88 eV) with a full width at half maximum (FWHM) of 42 nm (120 meV). Absence of emissions from QWs with n = 2 and 3 in the PL spectrum implies efficient energy funnelling from these QWs to the emissive centers of the PBA0.83PI film, i.e., QWs with larger n values and smaller band gaps. We calculated the band gaps of CsPbI3 QWs based on a model using the modified effective mass approximation.23 The calculation results match well with the experimental values for the CsPbI3 QWs with n = 1, 2, 3 and 4 (See Fig. S1 and related captions for details). Based on the calculation results (Fig. S1), the emissive centers of the PBA0.83PI film can be assigned as CsPbI3 QWs with n in the range of 5 to 7.

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Figure 1| PBA0.83PI perovskite films. a, Schematic diagram showing the structures of the layered lead iodide perovskites. b, AFM height image. c, Absorption and PL (405 nm excitation) spectra. d, Photo-induced changes in transient absorption spectra (ΔT/T) at selected probe delay times, which show photobleaching at PB1 (555 nm), PB2 (595 nm), PB3 (623 nm) and PB4 (660 nm). e, Normalized bleaching kinetics at 555 nm, 595 nm, 623 nm and 660 nm for the MQWs following excitation at 520 nm. f, Excitation-intensity-dependent PLQY (excitation wavelength: 405 nm). g, Integrated emission intensity as a function of sample temperature (excitation wavelength: 638 nm). The red line is the best-fitted curve with the model described in the text. 5


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The energy-funnel processes are confirmed by the transient absorption (TA) characterizations (Fig. 1d, 1e and S2). With 520 nm excitation, four bleach peaks at ~555, ~595, ~623 and ~660 nm, respectively, can be distinguished (Fig. 1d). Time traces of these photobleaching peaks are shown in Fig. 1e. The peaks at 555, 595 and 623 nm, which originate from QWs with n = 2, 3 and 4, respectively. The 555 and 595 peaks exhibit ultrafast decay with a time constant of ~0.5 ps. The 623 peak shows a quick increase in the first ~0.12 ps, followed by ultrafast decay within 1 ps. The peak at ~660 nm, which corresponds to emissive centers of the PBA0.83PI film, shows an initial increase with a time constant of ~0.4 ps. These facts indicate ultrafast cascade-like energy transfer processes from higher-energy QWs to lower-energy emissive centers, which suppress the blue tail in the PL spectrum. Excitation intensity-dependent PLQY measurements (Fig. 1f) show that the PLQY of the film increases from 48% to 58% when the excitation intensity increases from 0.3 to 5 mW/cm2. Further increasing the excitation intensity to 100 mW/cm2 leads to a slightly decreased PLQY of 46%, which may be associated with increased Auger recombination rates in the quantum-confined emissive centers.14 Furthermore, we conducted temperature-dependent PL measurements (Fig. S3) to reveal the charge recombination dynamics of the emissive centers in the MQWs film. In general, thermal quenching of PL reveals nonradiative decay channels for photogenerated carriers. Such nonradiative centers are generally thermally activated and hence largely determine the room-temperature internal quantum efficiency of luminescence.35 In our experiments, a 638 nm light was used to excite the PBA0.83PI MQW film so that the energy funnelling processes were avoided and only the behaviours of the emissive centers were revealed. Fig. 1g shows an Arrhenius plot of the integrated PL intensity (also can be regarded as the relative internal quantum efficiency) as a function of reciprocal temperature. The results can be well-fitted by a PL thermal quenching model,27,36 𝐼(𝑇) =

𝐼𝑂

(

∆𝐸𝑖 𝐵𝑇

1 + Σ𝐴𝑖exp ― 𝑘

) 6


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where 𝐼(𝑇) represents the integrated PL intensity at temperature T, I0 is the intensity at the low temperature limit, ∆𝐸𝑖 is the activation energy of a nonradiative channel, and Ai represents the possibility of nonradiative decay through certain channels. The fitting results indicate that for the PBA0.83PI film, there is only one thermal-activated nonradiative channel with a corresponding ∆𝐸 of ~170 meV. The high-quality PBA0.83PI MQW films encourage us to apply them in electroluminescence (EL) devices. Our PeLEDs consist of multiple layers of, in the following order, glass substrate with an indium tin oxide (ITO) coating, poly (ethylenedioxythiophene): polystyrene sulphonate (PEDOT: PSS, ~35 nm), poly [N,N’-bis(4-butylphenyl)-N,N’-bis(phenyl)-benzi] (poly-TPD, ~23 nm), PVK (~5 nm), PBA0.83PI MQW film (~20 nm), 2,2’,2’’-(1,3,5-benzinetriyl)tris(1-phenyl-1H-benzimidazole) (TPBi, ~80 nm), LiF (~1 nm) and Al (~100 nm). Fig. 2a shows a schematic of the flat-band energy-level diagram of the multiple layers is showed in Fig. 2a. In this device structure, the multilayers of PEDOT: PSS/poly-TPD/PVK are used as holeinjection layers and the TPBI film is used as electron-injection layer. A typical EL spectrum of our PeLED is shown in Fig. 2b. The EL emission shows a stable peak at 664 nm under various bias voltages. The EL spectrum represents Commission Internationale de L’Eclairage (CIE) color coordinates of (0.72, 0.27) (Fig. 2c), indicating color-saturated red emission. The current density−voltage−luminance (J−V−L) and EQE-current density characteristics of the PeLEDs are shown in Fig. 2d and 2e, respectively. The turn-on voltage (@ 0.1 cd/m2) is 2.6 V. At 6 V, a brightness of 968 cd m−2 is achieved. The peak EQE of our champion PBA0.83PI devices is 13.3%. A histogram of peak EQEs for 21 PBA0.83PI devices from 3 batches demonstrates an average value of ~11.6% and a relative deviation of ~5.3% (Fig. 2f), indicating good reproducibility of our high-efficiency red PeLEDs. Device lifetime data shown in in Fig. S4 indicates that our red PeLEDs exhibit operational stability inferior to the best green or infrared PeLEDs reported in literature.4,5 Understanding on the degradation mechanism, which is critical for improving device lifetime of PeLEDs based on MQW films, is a subject of our ongoing investigation. 7


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Figure 2| Device characteristics of the PeLEDs based on PBA0.83PI film. a, Flat-band energy level diagram. b, EL spectra at various biases. c, The corresponding CIE color coordinates. d, Current density-luminance-voltage characteristics. e, EQE-current density curve of a device. f, A histogram of peak EQEs measured from 21 devices.

The emission spectra of the red PeLEDs are readily tuned by adjusting the molar ratios of PBA cations in the precursor solutions. As shown in Fig. 3a, the emission peaks of the PBAxPI MQW films can be tuned from 640 to 680 nm simply by decreasing the molar ratio of PBAI: PbI2 while keeping the molar ratio of CsI: PbI2 as 0.92:1 in the precursor solution. For instance, a PBA0.5PI MQW film shows a PL peak 8


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at 684 nm with a FWHM of 34 nm (90 meV) while the PL peak of PBA1.0PI MQW film locates at 645 nm with an enlarged FWHM of 47 nm (142 meV). The PLQYs of PBA0.9PI, PBA0.83PI, PBA0.75PI and PBA0.65PI films are 39%, 48%, 42% and 35%, respectively (Fig. 3c). Applying the same device structure leads to PeLEDs with peak EQEs of 9.5±0.7%, 11.6±0.8%, 11.3±0.7%, and 10.6±0.6% corresponding to EL peaks at 650, 661, 669 and 680 nm, respectively. The detailed device characteristics are shown in Fig. S5.

Figure 3| PL and EL properties of perovskite MQW films processed from precursor solutions with different molar ratios of PBAI:PbI2 and BAI:PbI2. a and b, PL spectra. c, PLQY (excitation density: 0.3 mW/cm2, wavelength: 405 nm)-PL peak relationship. d, EQE-EL peak relationship.

To understand the impacts of L cations on the properties of lead-iodide MQW films, we grow MQW films with n-butylammonium (BA), instead of PBA, as the L cations. The corresponding perovskite films are abbreviated as BAxPI. The emission wavelengths of the BAxPI films can be tuned from 650 to 685 nm (Fig. 3b) by varying 9


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the molar ratio of BAI: PbI2 from 0.9 to 0.75 while keeping the molar ratio of CsI: PbI2 as 0.92: 1 in the precursor solutions. However, as shown in Fig. 3c, all the BAxPI MQW films show PLQYs of < 14%. As a result, the peak EQEs of the PeLEDs based on BA0.9PI, BA0.83PI and BA0.75PI MQWs (corresponding to EL peaks at 658, 670 and 680 nm) are 4.3±0.6%, 5±0.8% and 5.5±1.0%, respectively (Fig. 3d and S6). Device lifetime data of a BA0.83PI device is shown in in Fig. S7, indicating even shorter operational lifetime than those of the PBA0.83PI devices. We characterized a BA0.83PI film to understand the origins that cause the differences of PLQYs and EL properties between PBA0.83PI and BA0.83PI films. The results are shown in Fig. 4. AFM measurements (Fig. 4a) show that the BA0.83PI film possesses a smooth and uniform surface morphology with a root-mean-square roughness as low as 0.9 nm. Absorption spectrum of the BA0.83PI film (Fig. 4b) shows two excitonic peaks at 543 nm and 586 nm, which can be assigned as to the CsPbI3 QWs with n = 2 and 3, respectively. These two excitonic peaks are slightly blue-shifted comparing with those of the PBA0.83PI films, which may be explained by differences of both electronic structure and dielectric constant of the L cations.23,37 PL spectrum of the BA0.83PI film shows one main asymmetric peak at 668 nm. The FWHM of the main PL peak is 57 nm (162 meV), which is greater than that of the PBA0.83PI film. The PL spectrum on a semi-log scale reveals two emission peaks at 550 nm (2.25 eV) and 590 nm (2.10 eV), which can be assigned as emission from n=2 and n=3 QWs, respectively. Excitation intensity-dependent PLQY measurements (Fig. 4e) show that the PLQY increase significantly from 10% to 22% when the excitation density increases from 0.3 mW/cm2 to 100 mW/cm2. This result can be attributed to the trap filling effects, similar to that reported in bulk perovskites.38,39 TA results (as shown in Fig. 4c, d and S8) illustrate that the energy transfer processes between the QWs with various thicknesses. Nevertheless, the PL characteristics of the BA0.83PI film, including asymmetric emission spectrum and the two satellite peaks at 2.25 and 2.10 eV, suggest incomplete energy funnelling. This feature is different from that of the PBA0.83PI film. Next, we show that the dissimilar energy transfer processes of the two MQW films are due to the different distributions of QW thicknesses. Literature report suggests that 10


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the relative strength of TA signal (at 0.2 ps) of layered perovskites with different thicknesses, i.e., the QWs with different n values, can be used to estimate their distributions in the thin films.40 Here we adopt this method to analyse the distributions of QW thicknesses in the MQW films. For the BA0.83PI film, the bleach peak of the n=2 QWs is quite strong compared with that of n=3 QWs. The ratio of integral area of bleach peaks for n = 2 and n = 3 QWs is 0.80 (Fig. S9). In contrast, this ratio is 0.38 for PBA0.83PI film (Fig. S9). These results suggest that the fraction of n=2 QWs in BA0.83PI film is higher than that in PBA0.83PI films. This point is confirmed by the XRD analyses (Fig. S10). More importantly, TA signal (Fig. S9) of the PBA0.83PI film shows a much stronger photo bleach at ~655 nm than that of the BA0.83PI film, indicating a much higher fraction of large-n QWs in PBA0.83PI films. These structural features are in line with that the energy funnelling is much more complete in the PBA0.83PI films. Finally, we show that the exciton recombination dynamics of BA0.83PI film is different from that of BA0.83PI film. Temperature-dependent PL measurements were conducted on the BA0.83PI films (Fig. S11). Similarly, a 638 nm light was used to avoid the energy funnelling processes. The corresponding Arrhenius plot of the integrated PL intensity and temperature is shown in Fig. 4f. The best fit to the data gives two nonradiative channels with activation energy of ∆𝐸1 = 14.8±2 meV and ∆𝐸2 = 210±15 meV, respectively. This feature is distinctive from that of PBA0.83PI perovskite. Therefore, we suggest that the choice of L cations, which passivate the quantum quantum-confined perovskite emitters, can result in distinctive thermal-activated nonradiative recombination channels. The presence of the nonradiative channel with a small activation energy of ~14.8 meV, together with the incomplete energy transfer processes in the BA0.83PI film, contribute to the much lower PLQY at room temperature. In a previous study, the Sargent group showed that the PLQY of exfoliated (C6H5CH2NH3)2PbBr4 two-dimensional perovskites, ~60%, is substantially higher than that of exfoliated (BA)2PbBr4 perovskites, ~17%. The differences were attributed to crystal rigidity and exciton-phonon interactions induced by the ligands.41 Our finding demonstrate that for the all-iodide MQW films, the choices of the L cations can influence the distribution of QW thicknesses, the efficiency of energy funnelling 11


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processes, and the recombination dynamics at the emissive centers.

Figure 4| Structural and optical characteristics of the BA0.83PI film MQW film. a, AFM height image. b, Absorption and PL (the excitation source is a 405 nm laser ) spectra. c, TA spectra (ΔT/T) at selected probe delay times, which shows photobleaching at PB1 (548 nm), PB2 (592 nm), PB3 (620 nm) and PB4 (664 nm). d, Normalized bleaching kinetics at 548 nm, 592 nm, 620 nm and 664 nm for the MQW film following excitation at 520 nm. e, Excitation-intensitydependent PLQY (excitation wavelength: 405 nm). f, Integrated emission intensity as a function of the sample temperature (excitation wavelength: 638 nm). The red line is the best-fit curve with the model described in the text. 12


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In conclusion, we demonstrate efficient red PeLEDs based on MQWs of PBA2Csn−1PbnI3n+1. Through controlling the ratio of L cations in the precursor solutions, the thicknesses of the emissive all-iodide QWs in the MQW films can be wellcontrolled, allowing single-peak and stable red emission below 680 nm. We find that the choices of the L cations strongly influence the distribution of the QW thicknesses, the energy transfer process and the recombination channels of the emissive centers. These issues are crucial for achieving MQW films with desirable optical properties and thereby, high-efficiency red PeLEDs. Our study sheds light on rational design of highperformance perovskite MQW films towards their potential application as red light sources.

Methods

PbI2 (99.999%) and PVK (molecular weight: 25000−50000 g mol−1) were purchased from Sigma-Aldrich. Chlorobenzene (99.8%), m-xylene (99+%) and PBA (phenylbutylamine) (>98.0%) were purchased from Acros. We bought Hydroiodic acid (57 wt % in water), DMSO (99.9%) and CsI (99.999%) from Adamas. TPBi (98%) was purchased from J&K Chemical Ltd. Poly-TPD was purchased from American Dye Source. BAI were purchased from Xi'an Polymer Light Technology Corp. All these agents were used without further purification. The synthesis method of PBAI was same as a previous work of ours.10 Hydroiodic acid (1.740 mL) was added into a solution of phenylbutylamine (2 mL) in methanol (20 mL) at 0 °C and then stirred for 2 h. Next, the solution was evaporated at 50 °C to obtain precipitates which were washed three times with diethyl ether. The purified precipitates were then vacuum-dried at 30 °C for 24 h. The precursor solutions for the PBA0.83PI films and the BA0.83PI films were prepared by dissolving PBAI (14.4 mg), CsI (14.8 mg), and PbI2 (28.7 mg) in DMSO (1 mL), and BAI (11.2 mg), CsI (15.9 mg), and PbI2 (30.8 mg) in DMSO (1 mL), respectively. 13


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As for the device fabrication of red PeLEDs, PEDOT: PSS (Baytron P VP AL 4083, filtered through a 0.45 μm N66 filter) were spin-coated onto the ITO-coated glass substrates at 4000 r.p.m. for 45 s and annealed at 150 °C for 30 min. Poly-TPD (dissolved in chlorobenzene, 8 mg ml-1) and PVK (dissolved in m-xylene, 3 mg ml-1) were then spin-coated at 2,000 r.p.m. for 45 s in glove box. The PVK layers were annealed at 150 °C for 30 min before the deposition of the next layer. The perovskites films were prepared by spin-coating the precursor solutions at 4000 r.p.m. for 2 min, which were then annealed at 100 °C in glove box for 10 min. Finally, the electron transport layer (TPBi), LiF and Al electrodes were evaporated by Travato C300 through a shadow mask under high vacuum of ∼2× 10−7 Torr. The device area was defined by overlap of the ITO and the top electrodes. Steady-state PL spectra were obtained by using an Edinburgh Instruments (FLS920) spectrometer with a 200W Xe lamp was used as the excitation light source. PLQYs of the perovskite films were measured by a three-step method.42 The setup was made up of a xenon lamp (150 W, Zolix Instruments), monochromator (Zolix Instruments), optical fiber, a QE65000 spectrometer (Ocean Optics), and a homedesigned integrating sphere. The temperature-dependent PL measurements were performed in a closed-cycle helium cryostat. XRD experiments were conducted on an X’Pert PRO system operated with Cu Kα radiation (λ = 1.5406 Å) at 40 keV and 40 mA. For femtosecond transient absorption spectroscopy, the fundamental output from Yb: KGW laser (1030 nm, 220 fs Gaussian fit, 100 kHz, Light Conversion Ltd) was separated to two light beams. One was introduced to NOPA (ORPHEUS-N, Light Conversion Ltd) to produce a certain wavelength for pump beam (here we used 520 nm), the other was focused onto a YAG window to generate white light continuum as probe beam. The pump and probe overlapped on the sample at a small angle less than 10 °. The transmitted probe light from sample was collected by a linear CCD array. The characterization of PeLED devices were conducted by using a home-built system, which was made up of A Keithley 2400 source meter and an integration sphere (FOIS-1) coupled with a QE-Pro spectrometer (Ocean Optics) were used for the 14


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measurements, at room temperature in glove box.43 The devices were swept from zero bias to forward bias. Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: XX.XXX/XXXX. Detail of transient absorption spectra, temperature-dependent PL spectra, device characteristics and additional XRD measurement (PDF). Corresponding Author *E-mail: [email protected]; [email protected]; [email protected] Author Contributions #These authors contributed equally to this work.

Acknowledgement

This work was financially supported by the National Natural Science Foundation of China (51522209, 91733302, 51772271 and 61634001), the National Key Research and Development Program of China (2016YFB0401602), the Weng Hongwu Academic Innovation Research Fund of Peking University, the Natural Science Foundation of Jiangsu Province (BK20150043), the National Basic Research Program of ChinaFundamental Studies of Perovskite Solar Cells (2015CB932200), the Fundamental Research Funds for the Central Universities (2017XZZX001-03A) and the Weng Hongwu Academic Innovation Research Fund of Peking University.

References (1) Tan, Z. K.; Moghaddam, R. S.; Lai, M. L.; Docampo, P.; Higler, R.; Deschler, F.; Price, M.; 15


ACS Photonics 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Sadhanala, A.; Pazos, L. M.; Credgington, D.; Hanusch, F.; Bein, T.; Snaith, H. J.; Friend, R. H., Bright light-emitting diodes based on organometal halide perovskite. Nat. Nanotechnol. 2014, 9, 687-692. (2) Cho, H.; Jeong, S. H.; Park, M. H.; Kim, Y. H.; Wolf, C.; Lee, C. L.; Heo, J. H.; Sadhanala, A.; Myoung, N.; Yoo, S.; Im, S. H.; Friend, R. H.; Lee, T. W., Overcoming the electroluminescence efficiency limitations of perovskite light-emitting diodes. Science 2015, 350, 1222-1225. (3) Chiba, T.; Hayashi, Y.; Ebe, H.; Hoshi, K.; Sato, J.; Sato, S.; Pu, Y.-J.; Ohisa, S.; Kido, J., Anionexchange red perovskite quantum dots with ammonium iodine salts for highly efficient light-emitting devices. Nat. Photon. 2018, 12, 681-687. (4) Lin, K.; Xing, J.; Quan, L. N.; de Arquer, F. P. G.; Gong, X.; Lu, J.; Xie, L.; Zhao, W.; Zhang, D.; Yan, C.; Li, W.; Liu, X.; Lu, Y.; Kirman, J.; Sargent, E. H.; Xiong, Q.; Wei, Z., Perovskite light-emitting diodes with external quantum efficiency exceeding 20 per cent. Nature 2018, 562, 245-248. (5) Cao, Y.; Wang, N.; Tian, H.; Guo, J.; Wei, Y.; Chen, H.; Miao, Y.; Zou, W.; Pan, K.; He, Y.; Cao, H.; Ke, Y.; Xu, M.; Wang, Y.; Yang, M.; Du, K.; Fu, Z.; Kong, D.; Dai, D.; Jin, Y.; Li, G.; Li, H.; Peng, Q.; Wang, J.; Huang, W., Perovskite light-emitting diodes based on spontaneously formed submicrometre-scale structures. Nature 2018, 562, 249-253. (6) Wang, N.; Cheng, L.; Ge, R.; Zhang, S.; Miao, Y.; Zou, W.; Yi, C.; Sun, Y.; Cao, Y.; Yang, R.; Wei, Y.; Guo, Q.; Ke, Y.; Yu, M.; Jin, Y.; Liu, Y.; Ding, Q.; Di, D.; Yang, L.; Xing, G.; Tian, H.; Jin, C.; Gao, F.; Friend, R. H.; Wang, J.; Huang, W., Perovskite light-emitting diodes based on solution-processed self-organized multiple quantum wells. Nat. Photon. 2016, 10, 699-704. (7) Yuan, M.; Quan, L. N.; Comin, R.; Walters, G.; Sabatini, R.; Voznyy, O.; Hoogland, S.; Zhao, Y.; Beauregard, E. M.; Kanjanaboos, P.; Lu, Z.; Kim, D. H.; Sargent, E. H., Perovskite energy funnels for efficient light-emitting diodes. Nat. Nanotechnol. 2016, 11, 872-877. (8) Liang, D.; Peng, Y.; Fu, Y.; Shearer, M. J.; Zhang, J.; Zhai, J.; Zhang, Y.; Hamers, R. J.; Andrew, T. L.; Jin, S., Color-Pure Violet-Light-Emitting Diodes Based on Layered Lead Halide Perovskite Nanoplates. ACS Nano 2016, 10, 6897-6904. (9) Zhang, S.; Yi, C.; Wang, N.; Sun, Y.; Zou, W.; Wei, Y.; Cao, Y.; Miao, Y.; Li, R.; Yin, Y.; Zhao, N.; Wang, J.; Huang, W., Efficient Red Perovskite Light-Emitting Diodes Based on Solution-Processed Multiple Quantum Wells. Adv. Mater. 2017, 29, 1606600. (10) Si, J.; Liu, Y.; He, Z.; Du, H.; Du, K.; Chen, D.; Li, J.; Xu, M.; Tian, H.; He, H.; Di, D.; Lin, C.; Cheng, Y.; Wang, J.; Jin, Y., Efficient and High-Color-Purity Light-Emitting Diodes Based on In Situ Grown Films of CsPbX3 (X = Br, I) Nanoplates with Controlled Thicknesses. ACS Nano 2017, 11, 11100-11107. (11) Kumar, S.; Jagielski, J.; Kallikounis, N.; Kim, Y. H.; Wolf, C.; Jenny, F.; Tian, T.; Hofer, C. J.; Chiu, Y. C.; Stark, W. J.; Lee, T. W.; Shih, C. J., Ultrapure Green Light-Emitting Diodes Using TwoDimensional Formamidinium Perovskites: Achieving Recommendation 2020 Color Coordinates. Nano Lett. 2017, 17, 5277-5284. (12) Chang, J.; Zhang, S.; Wang, N.; Sun, Y.; Wei, Y.; Li, R.; Yi, C.; Wang, J.; Huang, W., Enhanced Performance of Red Perovskite Light-Emitting Diodes through the Dimensional Tailoring of Perovskite Multiple Quantum Wells. J. Phys. Chem. Lett. 2018, 9, 881-886. (13) Yang, X.; Zhang, X.; Deng, J.; Chu, Z.; Jiang, Q.; Meng, J.; Wang, P.; Zhang, L.; Yin, Z.; You, J., Efficient green light-emitting diodes based on quasi-two-dimensional composition and phase engineered perovskite with surface passivation. Nat. Commun. 2018, 9, 570. (14) Zou, W.; Li, R.; Zhang, S.; Liu, Y.; Wang, N.; Cao, Y.; Miao, Y.; Xu, M.; Guo, Q.; Di, D.; Zhang, L.; Yi, C.; Gao, F.; Friend, R. H.; Wang, J.; Huang, W., Minimising efficiency roll-off in high-brightness 16


Page 16 of 23

Page 17 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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perovskite light-emitting diodes. Nat. Commun. 2018, 9, 608. (15) Sun, Y.; Zhang, L.; Wang, N.; Zhang, S.; Cao, Y.; Miao, Y.; Xu, M.; Zhang, H.; Li, H.; Yi, C.; Wang, J.; Huang, W., The formation of perovskite multiple quantum well structures for high performance light-emitting diodes. npj Flexible Electronics 2018, 2, 12. (16) Tian, Y.; Zhou, C.; Worku, M.; Wang, X.; Ling, Y.; Gao, H.; Zhou, Y.; Miao, Y.; Guan, J.; Ma, B., Highly Efficient Spectrally Stable Red Perovskite Light-Emitting Diodes. Adv. Mater. 2018, 30, e1707093. (17) Xing, J.; Zhao, Y.; Askerka, M.; Quan, L. N.; Gong, X.; Zhao, W.; Zhao, J.; Tan, H.; Long, G.; Gao, L.; Yang, Z.; Voznyy, O.; Tang, J.; Lu, Z. H.; Xiong, Q.; Sargent, E. H., Color-stable highly luminescent sky-blue perovskite light-emitting diodes. Nat. Commun. 2018, 9, 3541. (18) Chen, P.; Meng, Y.; Ahmadi, M.; Peng, Q.; Gao, C.; Xu, L.; Shao, M.; Xiong, Z.; Hu, B., Chargetransfer versus energy-transfer in quasi-2D perovskite light-emitting diodes. Nano Energy 2018, 50, 615622. (19) Yang, M.; Wang, N.; Zhang, S.; Zou, W.; He, Y.; Wei, Y.; Xu, M.; Wang, J.; Huang, W., Reduced Efficiency Roll-Off and Enhanced Stability in Perovskite Light-Emitting Diodes with Multiple Quantum Wells. J. Phys. Chem. Lett. 2018, 9, 2038-2042. (20) Zhao, B.; Bai, S.; Kim, V.; Lamboll, R.; Shivanna, R.; Auras, F.; Richter, J. M.; Yang, L.; Dai, L.; Alsari, M.; She, X.-J.; Liang, L.; Zhang, J.; Lilliu, S.; Gao, P.; Snaith, H. J.; Wang, J.; Greenham, N. C.; Friend, R. H.; Di, D., High-efficiency perovskite–polymer bulk heterostructure light-emitting diodes. Nat. Photon. 2018, 12, 783-789. (21) Bekenstein, Y.; Koscher, B. A.; Eaton, S. W.; Yang, P.; Alivisatos, A. P., Highly Luminescent Colloidal Nanoplates of Perovskite Cesium Lead Halide and Their Oriented Assemblies. J. Am. Chem. Soc. 2015, 137, 16008-16011. (22) Akkerman, Q. A.; Motti, S. G.; Srimath Kandada, A. R.; Mosconi, E.; D'Innocenzo, V.; Bertoni, G.; Marras, S.; Kamino, B. A.; Miranda, L.; De Angelis, F.; Petrozza, A.; Prato, M.; Manna, L., Solution Synthesis Approach to Colloidal Cesium Lead Halide Perovskite Nanoplatelets with Monolayer-Level Thickness Control. J. Am. Chem. Soc. 2016, 138, 1010-1016. (23) Sichert, J. A.; Tong, Y.; Mutz, N.; Vollmer, M.; Fischer, S.; Milowska, K. Z.; Garcia Cortadella, R.; Nickel, B.; Cardenas-Daw, C.; Stolarczyk, J. K.; Urban, A. S.; Feldmann, J., Quantum Size Effect in Organometal Halide Perovskite Nanoplatelets. Nano Lett. 2015, 15, 6521-6527. (24) Fu, Y.; Zheng, W.; Wang, X.; Hautzinger, M. P.; Pan, D.; Dang, L.; Wright, J. C.; Pan, A.; Jin, S., Multicolor Heterostructures of Two-Dimensional Layered Halide Perovskites that Show Interlayer Energy Transfer. J. Am. Chem. Soc. 2018, 140, 15675. (25) Ban, M.; Zou, Y.; Rivett, J. P. H.; Yang, Y.; Thomas, T. H.; Tan, Y.; Song, T.; Gao, X.; Credington, D.; Deschler, F.; Sirringhaus, H.; Sun, B., Solution-processed perovskite light emitting diodes with efficiency exceeding 15% through additive-controlled nanostructure tailoring. Nat. Commun. 2018, 9, 3892. (26) Zhao, L.; Lee, K. M.; Roh, K.; Khan, S. U. Z.; Rand, B. P., Improved Outcoupling Efficiency and Stability of Perovskite Light-Emitting Diodes using Thin Emitting Layers. Adv. Mater. 2018, e1805836. (27) Gan, L.; Li, J.; Fang, Z.; He, H.; Ye, Z., Effects of Organic Cation Length on Exciton Recombination in Two-Dimensional Layered Lead Iodide Hybrid Perovskite Crystals. J. Phys. Chem. Lett. 2017, 8, 5177-5183. (28) Kawano, N.; Koshimizu, M.; Sun, Y.; Yahaba, N.; Fujimoto, Y.; Yanagida, T.; Asai, K., Effects of Organic Moieties on Luminescence Properties of Organic–Inorganic Layered Perovskite-Type 17


ACS Photonics 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Compounds. J. Phys. Chem. C. 2014, 118, 9101-9106. (29) Li, G.; Rivarola, F. W.; Davis, N. J.; Bai, S.; Jellicoe, T. C.; de la Pena, F.; Hou, S.; Ducati, C.; Gao, F.; Friend, R. H.; Greenham, N. C.; Tan, Z. K., Highly Efficient Perovskite Nanocrystal Light-Emitting Diodes Enabled by a Universal Crosslinking Method. Adv. Mater. 2016, 28, 3528-3534. (30) Zhao, L.; Yeh, Y. W.; Tran, N. L.; Wu, F.; Xiao, Z.; Kerner, R. A.; Lin, Y. L.; Scholes, G. D.; Yao, N.; Rand, B. P., In Situ Preparation of Metal Halide Perovskite Nanocrystal Thin Films for Improved Light-Emitting Devices. ACS Nano 2017, 11, 3957-3964. (31) Lu, M.; Zhang, X.; Bai, X.; Wu, H.; Shen, X.; Zhang, Y.; Zhang, W.; Zheng, W.; Song, H.; Yu, W. W.; Rogach, A. L., Spontaneous Silver Doping and Surface Passivation of CsPbI3 Perovskite Active Layer Enable Light-Emitting Devices with an External Quantum Efficiency of 11.2%. ACS Energy Lett. 2018, 1571-1577. (32) Jeong, B.; Han, H.; Choi, Y. J.; Cho, S. H.; Kim, E. H.; Lee, S. W.; Kim, J. S.; Park, C.; Kim, D.; Park, C., All-Inorganic CsPbI3 Perovskite Phase-Stabilized by Poly(ethylene oxide) for Red-LightEmitting Diodes. Adv. Funct. Mater. 2018, 28, 1706401. (33) Kaufman J.E., Christensen J.F., Lighting Handbook, Waverly Press, Maryland, 1972. (34) Stoumpos, C. C.; Cao, D. H.; Clark, D. J.; Young, J.; Rondinelli, J. M.; Jang, J. I.; Hupp, J. T.; Kanatzidis, M. G., Ruddlesden–Popper Hybrid Lead Iodide Perovskite 2D Homologous Semiconductors. Chem. Mater. 2016, 28, 2852-2867. (35) Leroux, M.; Grandjean, N.; Beaumont, B.; Nataf, G.; Semond, F.; Massies, J.; Gibart, P., Temperature quenching of photoluminescence intensities in undoped and doped GaN. J. Appl. Phys. 1999, 86 , 3721-3728. (36) De Giorgi, M. L.; Perulli, A.; Yantara, N.; Boix, P. P.; Anni, M., Amplified Spontaneous Emission Properties of Solution Processed CsPbBr3 Perovskite Thin Films. J. Phys. Chem. C. 2017, 121, 1477214778. (37) Tanaka, K.; Takahashi, T.; Ban, T.; Kondo, T.; Uchida, K.; Miura, N., Comparative study on the excitons in lead-halide-based perovskite-type crystals CH3NH3PbBr3 CH3NH3PbI3. Solid State Commun. 2003, 127, 619-623. (38) Deschler, F.; Price, M.; Pathak, S.; Klintberg, L. E.; Jarausch, D. D.; Higler, R.; Huttner, S.; Leijtens, T.; Stranks, S. D.; Snaith, H. J.; Atature, M.; Phillips, R. T.; Friend, R. H., High Photoluminescence Efficiency and Optically Pumped Lasing in Solution-Processed Mixed Halide Perovskite Semiconductors. J. Phys. Chem. Lett. 2014, 5, 1421-1426. (39) D'Innocenzo, V.; Srimath Kandada, A. R.; De Bastiani, M.; Gandini, M.; Petrozza, A., Tuning the light emission properties by band gap engineering in hybrid lead halide perovskite. J. Am. Chem. Soc. 2014, 136, 17730-17733. (40) Quintero-Bermudez, R.; Gold-Parker, A.; Proppe, A. H.; Munir, R.; Yang, Z.; Kelley, S. O.; Amassian, A.; Toney, M. F.; Sargent, E. H., Compositional and orientational control in metal halide perovskites of reduced dimensionality. Nat. Mater. 2018, 17, 900-907. (41) Gong, X.; Voznyy, O.; Jain, A.; Liu, W.; Sabatini, R.; Piontkowski, Z.; Walters, G.; Bappi, G.; Nokhrin, S.; Bushuyev, O.; Yuan, M.; Comin, R.; McCamant, D.; Kelley, S. O.; Sargent, E. H., Electronphonon interaction in efficient perovskite blue emitters. Nat. Mater. 2018, 17, 550-556 (42) deMello, J. C.; Wittmann, H. F.; Friend, R. H., An Improved Experimental Determination of External Photo luminescenece Quantum Efficiency. Adv. Mater. 1997, 9, 230-232. (43) Dai, X.; Zhang, Z.; Jin, Y.; Niu, Y.; Cao, H.; Liang, X.; Chen, L.; Wang, J.; Peng, X., Solutionprocessed, high-performance light-emitting diodes based on quantum dots. Nature 2014, 515, 96-99. 18


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Table of Contents (TOC)


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Figure 1| PBA0.83PI perovskite films. a, Schematic diagram showing the structures of the layered lead iodide perovskites. b, AFM height image. c, Absorption and PL (405 nm excitation) spectra. d, Photo-induced changes in transient absorption spectra (ΔT/T) at selected probe delay times, which show photobleaching at PB1 (555 nm), PB2 (595 nm), PB3 (623 nm) and PB4 (660 nm). e, Normalized bleaching kinetics at 555 nm, 595 nm, 623 nm and 660 nm for the MQWs following excitation at 520 nm. f, Excitation-intensitydependent PLQY (excitation wavelength: 405 nm). g, Integrated emission intensity as a function of sample temperature (excitation wavelength: 638 nm). The red line is the best-fitted curve with the model described in the text.


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Figure 2| Device characteristics of the PeLEDs based on PBA0.83PI film. a, Flat-band energy level diagram. b, EL spectra at various biases. c, The corresponding CIE color coordinates. d, Current density-luminancevoltage characteristics. e, EQE-current density curve of a device. f, A histogram of peak EQEs measured from 21 devices.


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Figure 3| PL and EL properties of perovskite MQW films processed from precursor solutions with different molar ratios of PBAI:PbI2 and BAI:PbI2. a and b, PL spectra. c, PLQY (excitation density: 0.3 mW/cm2, wavelength: 405 nm)-PL peak relationship. d, EQE-EL peak relationship.


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Figure 4| Structural and optical characteristics of the BA0.83PI film MQW film. a, AFM height image. b, Absorption and PL (405 nm excitation) spectra. c, Photo-induced changes in transient absorption spectra (ΔT/T) at selected probe delay times, which shows photobleaching at PB1 (548 nm), PB2 (592 nm), PB3 (620 nm) and PB4 (664 nm). d, Normalized bleaching kinetics at 548 nm, 592 nm, 620 nm and 664 nm for the MQW film following excitation at 520 nm. e, Excitation-intensity-dependent PLQY (excitation wavelength: 405 nm). f, Integrated emission intensity as a function of the sample temperature (excitation wavelength: 638 nm). The red line is the best-fit curve with the model described in the text.


High-Efficiency Red Light-Emitting Diodes Based on Multiple Quantum

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