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Surface passivation of bismuth-based perovskite variant quantum dots to achieve efficient blue emission Meiying Leng, Ying Yang, Zhengwu Chen, Wanru Gao, Jian Zhang, Guangda Niu, Dengbing Li, Haisheng Song, Jianbing Zhang, Song Jin, and Jiang Tang Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.8b03090 • Publication Date (Web): 14 Aug 2018 Downloaded from http://pubs.acs.org on August 14, 2018

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Surface passivation of bismuth-based perovskite variant quantum dots to achieve efficient blue emission Meiying Leng,†,‡,§ || Ying Yang,†,‡ || Zhengwu Chen,†,‡ Wanru Gao,†,‡ Jian Zhang, †,‡ Guangda Niu,†,‡ * Dengbing Li,†,‡ Haisheng Song,†,‡ Jianbing Zhang,†,‡ Song Jin,§ Jiang Tang†,‡ *

†

Sargent joint research center, Wuhan National Research Center for Optoelectronics (WNLO), Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, 430074, Hubei, P. R. China. ‡ School of Optical and Electronic Information, Huazhong University of Science and Technology,1037 Luoyu Road, Wuhan, 430074, Hubei, P. R. China. § Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States *E-mail: [email protected]; [email protected].

ABSTRACT Metal halide perovskite quantum dots (QDs) recently have attracted great research attentions. However, blue-emitting perovskite QDs generally suffer from low photoluminescence quantum yield (PLQY) because of easily formed defects and insufficient surface passivation. Replacement of lead with low toxicity elements is also preferred toward potential commercial applications. Here, we apply Cl-passivation to boost the PLQY of MA3Bi2Br9 QDs to 54.1% at the wavelength of 422 nm, a new PLQY record for blue emissive, lead-free perovskite QDs. Due to the incompatible crystal structures between MA3Bi2Br9 and MA3Bi2Cl9, and the careful kinetic control during the synthesis, Cl- anions are engineered to mainly locate on the surface of QDs acting as passivating ligands, which effectively suppress surface defects and enhance the PLQY. Our results highlight the potential of MA3Bi2Br9 QDs for applications of phosphors, scintillators and light emitting diodes. Keywords: MA3Bi2Br9, perovskite variant, quantum dots, Cl-passivation, high PLQY

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INTRODUCTION Quantum dots (QDs), possessing tunable optical and electrical properties as well as low temperature solution processability, have been studied intensively for decades.1-2 Particularly, lead halide perovskite QDs recently emerged as a promising member in QDs family, due to their high photoluminescence quantum yield (PLQY, ~90%), narrow full width at half maximum (FHWH, 12~25 nm), wide color gamut (~150% NTSC), low-cost synthesis and continuously tunable band gap by modifications of halide composition and crystal size.3-5 Above features make lead halide perovskite QDs as potential candidates for future light emitters and vivid display applications.6-9 Although the performance of perovskite QDs is highly impressive, the toxicity of lead still remains as the major obstacle toward commercial applications. Replacing Pb with non- or low-toxic metals (Bi, Sb and Sn etc.) plays an indispensable role in the further development of perovskites QDs. However, lead-free perovskites always encountered low PLQYs and stabilities.10-13 For example, Sn-based perovskite (CsSnX3) QDs showed rather low PLQY (the best is 0.14%) and poor stability, due to the intrinsic high-energy-lying Sn 5s2 states and defect states.14 More recently, our group have studied bismuth-based perovskite variant (A3Bi2X9, A=CH3NH3 or Cs, X = Cl, Br, I) QDs.15 However, PLQYs of these halide QDs are generally below 20%, inferior to Pb-based perovskite QDs, which is probably caused by the residual surface states and strong photon-phonon coupling.16 We also reported Cs3Sb2Br9 QDs with a PLQY of 46% but accompanied with a low moisture stability.17 Whether lead-free perovskite can compete with lead-based analogues, especially in terms of luminescence properties, remains an open question to this field. We are particularly interested in Bi-based perovskite variant QDs because Bi3+ (6s26p0) is isoelectronic to Pb2+ and may inherit the defect tolerance property18 as the valence band maximum (VBM) of these materials also consists of antibonding hybridization between Bi 6s and halide p orbitals, which upshifts the VBM so that the defects are typically shallow.19 More importantly, Bi-based QDs typically have large band gaps and mainly emit in deep blue and violet region, a region that high PLQY is


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always difficult for all kinds of perovskite QDs.20 For example, lead halide perovskite-(R1NH3)2[(R2NH3)2PbBr4](n-1)PbBr4 nanocrystals showed a high PLQY of 53% at the wavelength of 403-413 nm with an FWHM of 11 nm, despite the close to unity quantum yield for lead halide perovskites in the green and red region.21 The generally lower blue emission efficiency is because defect states for wide-bandgap semiconductors are more likely to serve as deep level recombination centers, in contrast to the shallow defects for narrow-bandgap semiconductors.22,23 One major source of such recombination centers are defects associated with dangling bonds on QD surface. 24 Blue emitting QDs generally have small size and hence large surface to volume ratio. Surface passivation is thus expected to play a vital important role in removing the dangling bonds and enhancing photoluminescence especially for blue or violet emitting QDs.25 Previous reports about lead-free perovskites mainly focused on the selection of non-toxic metals and optimization of synthesis procedure.26 The surface chemistry of lead-free perovskite variant QDs and effective passivation routes to suppress non-radiative recombination channels have rarely been explored thus far. Herein we report an effective Cl-passivation for (CH3NH3)3Bi2Br9 (MA3Bi2Br9) perovskite variant QDs to achieve a bright blue emission with PLQY up to 54.1% at the wavelength of 422 nm. This value is among the highest ones for lead-free perovskite nanocrystals or QDs in blue or deep blue emitting region. MA3Bi2Br9 QDs were synthesized by collaborate ligand assisted re-precipitation (Co-LARP) method,27 with bismuth bromide and bismuth chloride both serving as the precursor. We found that Cl-passivated MA3Bi2Br9 QDs presented suppressed defect states, smaller Stokes shift, and much higher PLQY at the same emission position compared to pure MA3Bi2Br9 QDs. The underlying mechanism is that Cl atoms mainly located on the surface probably due to the reaction kinetics and incompatible crystal structures between MA3Bi2Br9 and MA3Bi2Cl9. Thanks to the passivation effect, Cl-passivated MA3Bi2Br9 QDs also demonstrated a better photostability and storage stability than MA3Bi2Br9 QDs.


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RESULTS AND DISCUSSIONS Unlike Pb-based perovskites, MA3Bi2Br9 and MA3Bi2Cl9 have distinct crystal structures. MA3Bi2Br9 has two-dimensional (2-D) structure and MA3Bi2Cl9 has one dimensional (1-D) structure, as shown in Figure S1. MA3Bi2Br9 could be simply viewed as cutting along the direction of 3-D parent perovskite structure and every third Bi layer is removed, forming the 2-D structure. In contrast, MA3Bi2Cl9 is formed by removing every third Bi layer along the direction of parent 3-D structure, and in order to keep charge balance, (001) planes also need to be sliced leaving two thirds of Bi atoms, resulting in the final 1-D structure.28 For Pb-based perovskites, strong halide exchange occurs very quickly between different halide atoms due to the fast halide diffusion and compatible crystal structure, making it almost impossible to obtain core-shell structures between different lead halide perovskites.29,30 Theoretically, benefiting from their different crystal structures, it is possible to achieve core-shell or locally concentrated Cl- onto MA3Bi2Br9 QDs upon forming respective crystal structure. Such features may allow many interesting phenomenon, such as energy band engineering, surface states control, etc. To verify our hypothesis, MA3Bi2Br9 and MA3Bi2Cl9 powders were mixed together through grinding for 1h, and indeed no MA3Bi2(Cl,Br)9 alloy was generated based on powder x-ray diffraction (XRD) result (Figure S2). This observation suggests that once MA3Bi2Br9 and MA3Bi2Cl9 form in its own crystal structure separately, halide exchange between Br- and Cl- becomes difficult or even impossible. We want to utilize the structure incompatibility between MA3Bi2Br9 and MA3Bi2Cl9 to obtain Cl-passivated MA3Bi2Br9 QDs. A brief description of synthesis procedure is provided here. The synthesis of MA3Bi2(Cl,Br)9 perovskite QDs followed the Co-LARP method used for MA3Bi2Br9 QDs synthsis, and the relative ratio of Br- and Cl- was manipulated in the precursor solution. Namely, MABr, MACl, BiBr3 and BiCl3 with proper molar ratios (ranging from 0 to 100%) were dissolved in DMF. Same as our previous protocol, ethyl acetate was added into the precursor solution as the collaborate solvent, and octylamine was also addede to control the


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crystallization rate.27 The precursor solution was then injected into the anti-solvent (octane) with oleic acid dissolved as the ligand to stablize the colloidal solution. Finally, the bismuth-based perovskite variant QDs were successful synthesized and isolated. In the following discussions, we used Cl content in precursors to differentiate each sample (0%, 33.3%, 50%, 66.7%, 100% Cl sample).

Figure 1. Properties of Cl-passivated perovskite variant QDs. (a) Transmission electron microscopy (TEM) image. (b) HRTEM image of a typical QD. (c) Analysis of size distribution. (d) XRD pattern.

We carried out transmission electron microscopy (TEM) characterization on as-synthesized QDs to study their size and morphology. The TEM images and size distributions of MA3Bi2(Cl, Br)9 QDs are shown in Figure 1, Figure S3 and S4. As BiCl3 was introduced into the precursor, we found a size increase of the products: 3.94±0.75 nm for 0% Cl sample, 6.02±0.61 nm for 33.3% Cl sample, 5.97±0.79 nm for 50% Cl sample, 6.09±0.65 nm for 66.7% Cl sample, and 6.05±0.62 nm for 100% ACS Paragon Plus Environment

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Cl sample. The average size was calculated based on 100 randomly selected QDs from two different batches. We introduced the significance value (P-value)

31

, a

widely employed method to quantify the statistical significance of evidence under the null hypothesis, to study the effect of Cl incorporation. Based on the t-test, the P-value for the 0% and 33.3% Cl sample was calculated smaller than 0.001, demonstrating a significant size difference between these two samples. We thus conclude that a substantial size increase occurred upon Cl- introduction, which is probably due to the higher solubility of BiCl3 in DMF, resulting in less nucleation events and larger sizes of QD products. Further increase of Cl- might influence the number of active precursors for crystal growth, thereby restricting the further increase of crystal size. 0% Cl sample shows the same crystal structure as previously reported MA3Bi2Br9 QDs.15 For 33.3% Cl sample, the high resolution TEM image (Figure 1b) reveals a high crystallinity with a lattice spacing of 2.34 Å, 2.05 Å and 1.75 Å, corresponding to (300), (024) and (041) planes of hexagonal structure. Although Cl- was introduced in the precursors, above plane distances were the same as pure MA3Bi2Br9, indicating Cl- located onto the surface of QDs rather than doped into the crystal structure because otherwise lattice shrinkage would be observed. The selected-area electron-diffraction (SAED) pattern (inset of Figure 1b) confirms the high crystallinity of the Cl-passivated MA3Bi2Br9 perovskite QD. The interplanar spacing (calculated from SAED) of different planes in MA3Bi2(Cl, Br)9 perovskite QDs are listed in Table S3. 50% Cl samples exhibited lattice spacing slightly smaller than pure MA3Bi2Br9 while 66.7% Cl sample seems more like Br-doped MA3Bi2Cl9, with lattice spacing slightly larger than MA3Bi2Cl9. Figure 1d reveals the XRD pattern of 33.3% Cl sample. Glass was used as the substrate and exhibited no peak at 21.6o and 45.0o, thus excluding the influence of the substrate. The peak at 21.6° is attributed to (110) plane, and that at 45.0° belongs to (221) plane of MA3Bi2Br9. The peak position is identical to that of pure MA3Bi2Br9, further proving that there was no or rarely Cl- inside the QDs. The obvious broadening of the diffraction peaks is caused by the limited size of QDs. XRD ACS Paragon Plus Environment

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patterns of other MA3Bi2(Cl, Br)9 QDs are shown in Figure S5. The diffraction peaks and the calculated lattice for MA3Bi2(Cl, Br)9 QDs are listed in Table S4 and Table S5 which obviously showed that the 50% sample exhibits higher diffraction peaks and smaller lattice parameters, indicating the alloy of Cl and Br with the structure of MA3Bi2Br9. 66.7% sample was more like Br-doped MA3Bi2Cl9, with different crystal structures. echoing the previous SAED results. Above results demonstrated 33.3% Cl content generated Cl-passivated MA3Bi2Br9 QDs, 50% and 66.7% Cl content led to alloyed MA3Bi2(Cl, Br)9 QDs. The structure change as Cl content increased in precursors is probably due to the reaction kinetics and incompatible crystal structures between MA3Bi2Br9 and MA3Bi2Cl9. For the mixed precursor solution with low content of Cl (33.3%), BiCl3 precipitated later than BiBr3 because of its lower concentration and higher solubility. It is thus expected that Br rich or even pure Br-based perovskite nucleus formed first, and Cl concentrated on the surface of MA3Bi2Br9 QDs. As Cl content further increased to 50%, the nucleation rate of MA3Bi2Cl9 became competitive to MA3Bi2Br9. Upon the simultaneous precipitation of Cl and Br precursors, MA3Bi2Br9 QDs partially doped with Cl- were produced. Above phase segregation is similar to the case of MAPbI3-xBrx series. Previous theoretical and experimental studies showed that due to the different crystal structures, MAPbI3 and MAPbBr3 can only form a thermodynamically stable phase of MAPbIBr2 at low iodide feeding ratio and a continuous solid solution at higher iodide content.32-34


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Figure 2. Composition-related photoluminescence for MA3Bi2(Cl, Br)9 perovskite variant QDs. (a) Raman spectra. (b) Photographs of QD solutions under a 325 nm UV lamp excitation. (c) Absorption and photoluminescence spectra. (d) Time-resolved photoluminescence spectra.

Raman measurements were used to monitor the composition of as-synthesized QDs with different contents of Cl and Br. Figure 2a shows the Raman spectra of several MA3Bi2(Cl, Br)9 perovskite QDs powders. Two distinct Raman peaks located at 180 and 257 cm-1 were observed, respectively. The first peak at 180 cm-1 is attributed to Bi-Br bond from Bi-Br octahedra35 while the second peak at 257 cm-1 belongs to Bi-Cl bond in Bi-Cl octahedra36. The relative intensity of Bi-Cl bond in QDs suspension solution increases apparently along with the increase of Cl content in precursors, while the intensity of Bi-Br bond gradually weakens.

Table 1. Summary of emission peaks, absorption peaks, Stokes shifts and PLQY for colloidal MA3Bi2(Cl, Br)9 QDs with different adding ratios of Cl. Amount of Cl (Cl/ (Cl+Br))

PL peak (nm)

Abs Peak (nm)

Stokes shift (nm)

PLQY (%)

0%

422

376

46

13.5

33.3%

422

388

34

54.1


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50%

412

366

46

19.1

66.7%

399

353

46

22.4

100%

370

333

37

24.7

To directly compare the photoluminescence of these QDs, we imaged them under UV light excitations (Figure 2b). We found that 33.3% Cl sample exhibited brightest blue emission. To quantify these observations, UV-vis and photoluminescence (PL) spectroscopy were performed for QDs solution, which was shown in Figure 2c. As for absorption, 0% Cl sample, i.e. pure MA3Bi2Br9, showed an absorption peak around 376 nm, almost the same as the value reported before15. Quantum confinement exists in MA3Bi2Br9 QDs, since there is an obvious blue shift for absorption band edge and photoluminescence of MA3Bi2Br9 QDs compared to bulk MA3Bi2Br9 single crystals (Table S2). As the concentration of Cl increased, the absorption peak firstly red shifted to 388 nm (33.3% Cl), and then continuously blue shifted (50%, 66.7% Cl) until the perovskite variant turned into MA3Bi2Cl9 completely. The firstly observed red-shift is attributed to the increased size of Cl-passivated perovskite QDs from 3.94 nm (0% Cl) to 6.02 nm (33.7% Cl), as revealed by TEM results. Since the radius of Cl- is 0.18 nm and the mean size of 33.3% Cl sample is 6.02 nm, the net size of MA3Bi2Br9 core is calculated as (6.02-4*0.18) =5.3 nm, which is still larger than 0% Cl sample (3.94 nm), explaining the observed red shift in absorption. The blue-shift for 50% and 66.7% Cl sample was due to the anion mixing of Cl and Br in the perovskite QDs, i.e. forming alloyed QDs, and thus increasing the band gap of the products. For photoluminescence, a single peak was present in the 0% Cl sample centering at 422 nm, close to our previously reported value for MA3Bi2Br9 QDs. For 33.3% Cl content, the peak position preserved unchanged with respect to 0% Cl sample, which is in contradictory to the change of band gaps (absorption peaks red shifted from 376 nm to 388 nm as shown in Figure 2c). Fundamentally, the band gaps and surface defect-induced recombination together determine the emission peaks.37,38 We attributed the unchanged PL peak to the reduced surface defects after Cl introduction.


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Other evidences such as decreased PL lifetime and decreased FWHM (will present later) all support that surface defects have been well reduced. Thereby the combined effect of size increase and suppressed defects together make the PL peak unchanged. It should be noted that further increase of Cl content (>33.3%) led to the increase of Stokes shift, as well as the blue shift of the PL emissions, the same as the change of absorption peaks, as detailed in Table 1. The increase of Stokes shift might be attributed to the re-appeared surface defects. The blue shift of PL emission was due to the Cl alloying into MA3Bi2Br9 forming MA3Bi2(Cl, Br)9 QDs. The variation of PLQY inversely correlated with the Stokes shifts, and the 33.3% Cl sample peaked the PLQY (54.1%). The PLQY values were determined using a fluorescence spectrometer (Edinburgh FLS980 spectrofluorometer) with an integrating sphere. Current PLQY value is remarkably high and indicates few non-radiative decay pathways. (For more details of the PL, PLQY and absorption spectra, please find in Figure S6) Furthermore, the PLQY of the samples with Cl ratios around 33.3% are listed in Table S6 while the composition-related photoluminescence for MA3Bi2(Cl, Br)9 perovskite QDs is shown in Figure S7. Some previous papers demonstrated that Bi-based perovskite bulks can form self-trapped excitons (STE) in the excited states, where excitons are trapped in a state with the assistance of strong electron-phonon coupling.16 STE states generally produce photoluminescence with larger FWHM and more stokes shift compared to free excitons. Therefore the observed large FWHM and big stokes shift also indicate the presence of STE in MA3Bi2Br9 QDs.

Table 2. PL lifetime for colloidal MA3Bi2(Cl, Br)9 QDs with different ratio of Cl and Br in the precursor solution. Amount of Cl

A1 (%)

τ1 (ns)

A2 (%)

τ2 (ns)

0%

80.1

2.83

19.9

9.96

33.3%

100

2.17

N/A

N/A

50%

43

1.47

57

6.06

66.7%

55.4

1.9

44.6

7.06


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100%

88

1.24

12

7.5

Time-resolved photoluminescence measurements were applied to gain more insight into the exciton recombination dynamics. We note that the PL decay of MA3Bi2Br9 QDs is approximately double exponential with a short-time component of 2.83 ns and a long-time component of 9.96 ns. Here the short-time component is attributed to exciton recombination and the long-time component related to surface trap related recombination.39,40 Surprisingly, 33.3% Cl sample exhibited a mono-exponentially fitted decay with a short lifetime of 2.17 ns (Table 2), which demonstrated the perfect passivated surface for this sample.41 PL decays of other samples with further increased Cl content were well-fitted by double exponential curves, manifesting that defects appeared again (Figure 2d). Therefore, we believe only those Cl atoms residing onto the QDs’ surface can help suppress the surface defects and thus significantly enhance the light emitting property.

Figure 3. Characterization of Cl-passivated MA3Bi2Br9 QDs. (a) Passivation model. (b) XRF spectra of a typical sample of Cl-passivated MA3Bi2Br9 QDs. (c) Relationship between the percentage of the surface atom based on the passivation model. (d-f) XPS spectra of Bi 4f (d), Cl 2p (e), and Br 3d (f).


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To determine the actual ratio of Cl/(Cl+Br), X-ray fluorescence characterization (XRF) was applied on 33.3% Cl, 50% Cl and 66.7% Cl QDs powders. For XRF measurement, we firstly calibrated the facility using commercially available BiBr3 and BiCl3. Then the sample was measured with several randomly selected spots to obtain the average value. Such method has been adopted in previous paper using similar method (Energy-dispersive spectroscopy: EDS).27 We believe after the calibration the XRF result can present the real composition of the product. As shown in Figure 3b and S8, 33.3%, 50% and 66.7% Cl samples present a Cl/(Cl+Br) molar ratio of 14.0%, 41.7% and 58.2%, respectively. The lower actual ratio than precursor ratio implies Cl is hard to be fully incorporated into the MA3Bi2Br9 QDs. In order to further understand the specific structure of Cl-passivated MA3Bi2Br9 QDs (33.3% Cl sample), we established a simple model to correlate the particle size and the Cl/(Cl+Br) molar ratio, assuming that the surface of QDs was terminated with Cl atoms. The model was established based on the unit cell with obvious surface atom (Figure 3a). Details of the model are shown in Table S1 and Figure S9. Derived from the model, we calculated the Cl/(Cl+Br) ratio for 6.02 nm Cl-passivated MA3Bi2Br9 QDs as 13.6% (Figure 3c), which was highly consistent with the XRF result (14.0%). Therefore, it is believed that Cl-passivated MA3Bi2Br9 QDs have a halogen-rich surface and most of the surface bromide was replaced by chloride. X-ray photoelectron spectroscopy (XPS) measurements were also performed to further investigate the surface composition of pure Cl-passivated MA3Bi2Br9 QDs. As shown in Figure 3d, the Bi 4f spectrum can be divided into four peaks located at 158.2, 159.7, 163.4 and 164.9 eV, which indicates that there were two states of Bi in the Cl-passivated MA3Bi2Br9 QDs. One was related to the binding energy of MA3Bi2Br9 (158.2 and 163.4 eV), and the other to surface Bi3+ ions coordinated with Cl- (159.7 and 164.9 eV).42,43 By integrating the area for peaks represent to Bi-Cl and Bi-Br in the Bi 4f XPS spectrum, the Cl/Br ratio was calculated as 14.5%, which again supported the XRF results (14.0%). As shown in Figure 3e and 3f, Br 3d and Cl 2p spectra could be perfectly fitted with Gaussian−Lorentzian peaks, and its binding energies were in good agreement with the expected value in MA3Bi2Br9 ACS Paragon Plus Environment

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and MA3Bi2Cl9. The N 1s spectrum of MA3Bi2Br9 QDs shows two peaks with binding energy of 396.8 and 400.8 eV, indicating two existing chemical conditions of the N elements, one belongs to methyl ammonium, and the other was attributed to the surface octylamine(Figure S10).

Figure 4. Optical properties of Cl-passivated MA3Bi2Br9 QDs and pure MA3Bi2Br9 QDs. (a) Pseudocolor map of temperature-dependent PL spectra of Cl-passivated MA3Bi2Br9 QDs. (b) The correlation between integrated PL intensity and temperature derived from a, where exciton binding energy was extracted by fitting the curve. (c) Pseudocolor map of temperature-dependent PL spectra of pure MA3Bi2Br9 QDs. (d) The correlation between integrated PL intensity and temperature derived from c.

After determining the structure of Cl-passivated MA3Bi2Br9 QDs, we further studied their temperature related photoluminescence (Figure 4a and c). As shown in


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Figure S11, both pure QDs and Cl-passivated QDs exhibit an obvious PL intensity decrease with increasing temperature. The integrated PL intensity was plotted as a function of temperature using the following equation44:

IሺTሻ =

‫ܫ‬଴ 1 + ‫݌ݔ݁ܣ‬ሺ‫ܧ‬௕ /݇஻ ܶሻ

where I0 is the intensity at 0 K, Eb is the activation energy for exciton to dissociate into free carriers or for excitons to annihilate by non-radiative trap states, and kB is Boltzmann constant. Higher activation energy is beneficial for the stabilization of excitons and for efficient photoluminescence.45 Figure 4b and d show the integrated PL intensity versus temperature. The activation energies are estimated to be 100.8 meV and 259.1 meV for pure MA3Bi2Br9 and Cl-passivated MA3Bi2Br9 QDs, respectively. The higher activation energy of Cl-passivated QDs might come from the surface depletion induced quantum confinement, as observed in CdS nanostructures.46 Such a higher activation energy in Cl-passivated QDs favors radiative recombination and leads to brighter emission.47 We further studied the stability of as-synthesized QDs. The storage stability at room temperature with a humidity of ~60% has been studied (Figure S12). After 26 days, PL peak of Cl-passivated MA3Bi2Br9 QDs slightly blue shifted from 422 nm to 417 nm and the PL intensity decreased to 85% of initial intensity, while PL peak of pure MA3Bi2Br9 QDs shifted from 422 nm to 397 nm and its intensity degraded to 48% of initial value. The photostability of Cl-passivated MA3Bi2Br9 QD solutions was also studied (Figure S13) by illuminating the QD solutions with a portable UV lamp (365 nm, 6 W) at a 1 cm distance. The samples only exhibited a 12% reduction in PL intensity after 12 h illumination, much slower than the MA3Bi2Br9 QDs without Cl-passivation (relative PL intensity decay: 64%). PL enhancement was found at the beginning of this test due to the so-called “photoactivation” phenomenon, which probably originates from the smoothing of QDs and the removal of dangling bonds.48 Overall, the good storage stability and UV stability verified the good thermodynamic stability of the Cl-passivated MA3Bi2Br9 QDs. At last, the photoluminescence properties for blue emitting perovskite QDs or nanocrystals were summarized in Table


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3. Our Cl-passivated MA3Bi2Br9 QDs exhibited high PLQY, proper FWHM and decent photostability in the deep blue region. In terms of potential applications, Cl-MA3Bi2Br9 QDs may serve as effective scintillators for X-rays or gamma rays.49,50 Firstly, Bi-based perovskites contain heavy metal Bi, which ensures the effective attenuation of X-rays and gamma rays. Secondly, the large Stokes shift renders them a low self-absorption effect compared to Pb-based perovskites, which gives a high light yield under radiations. Thirdly, to capture the light from scintillators, PMT or Si APD is typically used as the detectors, which has the highest response wavelength at 420 nm. Assembling these QDs into films as scintillators is still undergoing.

Table 3. Properties comparison of different perovskite QDs with deep blue emissions. QDs

PL peak (nm)

PLQY (%)

FWHM (nm)

Eb (meV)

422

54.1

41

259.1

Cl-MA3Bi2Br9

Remnant PL Intensity 89%

Ref

This work

(after 12 h, 365 nm) MA3Bi2Br9

422

13.5

62

100.8

36%

This work

(after 12 h,365 nm) Cs3Bi2Br9

410

19.4

48

210.7

80%

51

(after 78h, 365 nm) Cs3Sb2Br9

410

46

41

548

50%

17

(after 108h, 365 nm) CsPbCl3

408

10

/

/

22%

52

(after 60 min, 2000W) B-MDs*

403

53

19

/

/

21

* represents (R1NH3)2[(R2NH3)2PbBr4](n-1)PbBr4 microdisks, while R1 is a long octyl chain, R2 is benzyl group, and n represents the number of layers.

CONCLUSION In summary, we have successfully obtained Cl-passivated MA3Bi2Br9 QDs with an emission peak at 422 nm, FWHM of 41 nm, and a PLQY of 54.1%. TEM and XRD


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analysis confirmed that the Cl-passivated MA3Bi2Br9 QDs exhibited the same crystal lattice with pure MA3Bi2Br9 phase, indicating that Cl- mainly located on the surface and passivated the surface defects likely due to reaction kinetic control and incompatible crystal structure between MA3Bi2Br9 and MA3Bi2Cl9. Overall, the high PLQY, coupled with low-toxicity and decent photo-stability made MA3Bi2Br9 perovskite QDs very competitive for potential applications including phosphors, scintillators and light emitting diodes.

EXPERIMENTAL SECTION Chemicals. All reagents were used without any purifications. BiCl3 (bismuth trichloride, 99.99%) was purchased from Shanghai Macklin Biochemical Co., Ltd., BiBr3 (bismuth tribromide, 99%) was purchased from Alfa Aesar, n-octylamine (≥99%) and oleic acid (≥90%) were purchased from Aladdin, n-octane (Super dry) was bought from J&K chemical CO., Ltd, China. Methylamine (CH3NH2, 30wt% in absolute ethanol), hydrobromic acid (HBr, 57wt% in water), hydrochloric acid (HCl, 37wt% in water), N,N-dimethylformide (Analytical grade), Ethyl acetate (Analytical grade) methanol anhydrous (Analytical grade) and ethanol anhydrous (Analytical grade) were all purchased from Sinopharm Chemical Reagent Co., Ltd, China). Synthesis of MAX (X = Cl, Br). MAX was synthesized by reaction of methylamine with hydrohalic acid (HBr for instance). 30 ml 30 wt% methylamine (MA) in absolute ethanol was stirred and cooled in ice-bath, and then the addition of 23 ml hydrobromic acid was assisted by a separating funnel with the speed of 2 drops per second. The reaction solution was stirred until all MA reacted. Then rotary evaporation was applied to obtain MABr powder with a pressure of 1 MPa at 60 oC. The snow-white powder was washed three times with diethyl ether and dried under vacuum (60 oC, 24 h) for future use. Synthesis of hybrid MA3Bi2(Cl, Br)9 QDs. Colloidal MA3Bi2(Cl, Br)9 QDs were synthesized following the Co-LARP technique. In a typical synthesis of MA3Bi2Br9


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QDs, 0.2 mmol MABr was dissolved in 1 mL DMF while 0.134 mmol BiBr3 was dissolved in 1mL ethyl acetate. These two solutions were mixed together to form the precursor solution with the extra addition of 20 µL n-octylamine to the mixture. 0.5 mL precursor solution was injected into 5 mL octane containing 0.625 mL oleic acid with vigorous stirring. The solution was centrifuged at 8000 rpm for 10 min to discard the large particles, and then clear pale-yellow QDs supernatant was obtained. MA3Bi2(Cl, Br)9 QDs were fabricated by using MABr, MACl, BiBr3 and BiCl3 with proper ratios. The ratio of Cl/(Cl+Br) ranged from 0 to 100%. Structural characterizations. Raman spectrum (Horiba JobinYvon, LabRAM HR800, 532 nm excitation) was applied to analyze the reaction. Transmission electron microscopy (TEM, TecnaiG2 20U-TWIN) was used to characterize the as-synthesized MA3Bi2(Cl, Br)9 QDs. The compositions of MA3Bi2(Cl, Br)9 QDs were obtained through X-Ray Fluorescence (EAGLE III, EDAX Inc, American). X-ray photoelectron spectroscopy (XPS) using Al Kα excitation (Genesis, EDAX Inc. 300W) was applied to analyze the chemical nature of QDs. The structure of MA3Bi2Br9 QDs was investigated by X-ray diﬀraction (XRD) with Cu Kα radiation (Philips, X pert pro MRD). It is difficult to directly precipitate MA3Bi2Br9 QDs by centrifugation. To preserve the particle size and avoid aggregations, we prepared the solid powder of MA3Bi2Br9 QDs and 33.3% Cl-samples by adding 1µL ethanedithiol (EDT) to 1mL CQDs solution for ligand exchange and then centrifuging at 8000 rpm for precipitation. However, for 50%, 66.7% and 100% Cl samples, we found that there are no precipitates even after adding EDT. Thereby we directly dried the solutions at 80 oC by rotary evaporation and added octane until precipitates were found. The precipitates then easily aggregated and led to the narrow diffraction peaks. Optical characterizations. The transmission and absorption spectra were measured on a UV-vis spectrophotometer (PerkinElmer Instruments, Lambda 950 using integrating sphere). PL measurements of MA3Bi2(Cl, Br)9 QDs were carried out using an Edinburgh instruments Ltd. UC920. The absolute PLQYs of diluted MA3Bi2(Cl, Br)9 QDs solution were determined using a fluorescence spectrometer (Edinburgh FLS980 spectrofluorometer) with an integrating sphere. Samples were excited at a ACS Paragon Plus Environment

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wavelength of 330 nm using a xenon lamp source. The time-resolved PL spectra were collected on an Edinburgh FLS920. Excitation wavelengths were at 334 nm. The temperature-dependent PL spectra measurements were recorded using Horiba JobinYvon, LabRAM HR800 spectrometer and excited with a 325 nm laser with temperature ranging of 120 K to 300 K using a liquid helium cooler. The light source used in photostability study was a 365 nm UV lamp (JIAP ENG, ZF-05, China).

ASSOCIATED CONTENT Supporting Information Available: size distribution, details of PL and absroption, TEM images, XPS spectrum and photostability of MA3Bi2(Cl, Br)9 QDs. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *Email: [email protected] *Email: [email protected]

Author Contributions M. Leng and Y. Yang contributed equally to this work. Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENT This work was financially supported by the Major State Basic Research Development Program of China (2016YFB0700702), the National Natural Science Foundation of ACS Paragon Plus Environment

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China (5171101030, 61725401 and 51702107), the Huazhong University of Science and Technology (HUST) Key Innovation Team for Interdisciplinary Promotion (2016JCTD111). S. Jin acknowledge support by the Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under award DE-FG02- 09ER46664. The authors would like to thank the Analytical and Testing Center of HUST, Electron Microscopy Testing Center of WNLO, Dr. J. Su for assistance with TEM characterization, Mr. J. Duan for PL measurements help.

REFERENCES 1. Alivisatos, A. P. Science 1996, 271, 933-937. 2. Klimov, V. I.; Mikhailovsky, A. A.; Xu, S.; Malko, A.; Hollingsworth, J. A.; Leatherdale, C. A.; Eisler, H.-J.; Bawendi, M. G. Science 2000, 290, 314-317. 3. Huang, H.; Zhao, F.; Liu, L.; Zhang, F.; Wu, X. G.; Shi, L.; Zou, B.; Pei, Q.; Zhong, H. ACS Appl. Mater. Interfaces 2015, 7, 28128-28133. 4. Bai, S.; Yuan, Z.; Gao, F. J. Mater. Chem. C 2016, 4, 3898-3904. 5. Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. Nano Lett. 2015, 15, 3692-3696. 6. Zhang, J.; Yang, Y.; Deng, H.; Qiao, K.; Farooq, U.; Ishaq, M.; Yi, F.; Liu, H.; Tang, J.; Song, H. Nano-Micro Lett. 2017, 9, 36. 7. Zhang, X.; Lin, H.; Huang, H.; Reckmeier, C.; Zhang, Y.; Choy, W. C.; Rogach, A. L. Nano Lett. 2016, 16, 1415-1420. 8. Gong, X.; Yang, Z.; Walters, G.; Comin, R.; Ning, Z.; Beauregard, E.; Adinolfi, V.; Voznyy, O.; Sargent, E. H. Nat. Photonics 2016, 10, 253-257. 9. Shirasaki, Y.; Supran, G. J.; Bawendi, M. G.; Bulović, V. Nat. Photonics 2012, 7, 13-23. 10. Yang, B.; Chen, J.; Mao, F.; Hong, X.; Zheng, K.; Yang, S.; Li, Y.; Pullerits, T.; Deng, W.; Han, K. Angew. Chem. Int. Ed. 2017, 56, 12471–12475. 11. Pal, J.; Manna, S.; Mondal, A.; Das, S.; Adarsh, K. V; Nag, A. Angew. Chem. Int.

Ed. 2017, 56, 14187–14191.


Nano Letters 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

12. Wang, A.; Guo, Y.; Muhammad, F.; Deng, Z. Chem. Mater. 2017, 29, 6493–6501. 13. Zhou, C.; Lin, H.; Tian, Y.; Yuan, Z.; Clark, R.; Chen, B.; van de Burgt, L. J.; Wang, J. C.; Zhou, Y.; Hanson, K.; Meisner, Q. J.; Neu, J.; Besaa, T.; Siegrist, T.; Lambers, E.; Djurovich, P.; Ma, B. Chem. Sci. 2018, 9, 586. 14. Jellicoe, T. C.; Richter, J. M.; Glass, H. F.; Tabachnyk, M.; Brady, R.; Dutton, S. E.; Rao, A.; Friend, R. H.; Credgington, D.; Greenham, N. C.; Bohm, M. L. J. Am.

Chem. Soc. 2016, 138, 2941-2944. 15. Leng, M.; Chen, Z.; Yang, Y.; Li, Z.; Zeng, K.; Li, K.; Niu, G.; He, Y.; Zhou, Q.; Tang, J. Angew. Chem. Int. Ed. 2016, 55, 15012-15016. 16. McCall, K. M.; Stoumpos, C. C.; Kostina, S. S.; Kanatzidis, M. G.; Wessels, B. W.

Chem. Mater. 2017, 29, 4129-4145. 17. Zhang, J.; Yang, Y.; Deng, H.; Farooq, U.; Yang, X.; Khan, J.; Tang, J.; Song, H.

ACS nano 2017, 11, 9294−9302. 18. Hoye, R. L.; Brandt, R. E.; Osherov, A.; Stevanović, V.; Stranks, S. D.; Wilson, M. W.; Kim, H.; Akey, A. J.; Perkins, J. D.; Kurchin, R. C.; Poindexter, J. R.; Wang, E.; Bawendi, M. G.; Bulović, V.; Buonassisi, T. Chem-Eur J. 2016, 22, 2605-2610. 19. Kim, J.; Chung, C. H.; Hong, K. H. Phys.Chem.Chem.Phys. 2016, 18, 27143. 20. Song, J.; Li, J.; Li, X.; Xu, L.; Dong, Y.; Zeng, H. Adv. Mater. 2015, 27, 7162-7167. 21. Yuan, Z.; Shu, Y.; Tian, Y.; Xin, Y.; Ma, B. Chem. Commun. 2015, 51, 16385-16388. 22. Kim, J.; Chung, C. H.; Hong, K. H. Phys. Chem. Chem. Phys. 2016, 18, 27143-27147. 23. Yin, W. J.; Yang, J. H.; Kang, J.; Yan, Y.; Wei, S. H. J. Mater. Chem. A 2015, 3, 8926-8942. 24. Koscher, B. A.; Swabeck, J. K.; Bronstein, N. D.; Alivisatos, A. P. J. Am. Chem.

Soc. 2017, 139, 6566−6569 25. Hines, D. A.; Kamat, P. V. ACS Appl. Mater. Interfaces 2014, 6, 3041-3057. 26. Wang, A.; Yan, X.; Zhang, M.; Sun, S.; Yang, M.; Shen, W.; Pan, X.; Wang, P.; Deng, Z. Chem. Mater. 2016, 28, 8132-8140. ACS Paragon Plus Environment

Page 20 of 23

Page 21 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

Nano Letters

27. Zhang, F.; Zhong, H.; Chen, C.; Wu, X.; Hu, X.; Huang, H.; Han, J; Zou, B.; Dong, Y. ACS Nano 2015, 9, 4533-4542. 28. Li, M.; Hu, Y.-Q.; Bi, L.-Y.; Zhang, H.-L.; Wang, Y.; Zheng, Y.-Z. Chem. Mater. 2017, 29, 5463-5467. 29. Guhrenz, C.; Benad, A.; Ziegler, C.; Haubold, D.; Gaponik, N.; Eychmüller, A.

Chem. Mater. 2016, 28, 9033-9040. 30. Wang, H. C.; Lin, S. Y.; Tang, A. C.; Singh, B. P.; Tong, H. C.; Chen, C. Y.; Lee, Y. C.; Tsai, T. L.; Liu, R. S. Angew. Chem. Int. Ed. 2016, 55, 7924-7929. 31. Wasserstein, R. L.; Lazar, N. A. Am. Stat. 2016, 70, 129-133. 32. Rosales, B. A.; Men, L.; Cady, S. D.; Hanrahan, M. P.; Rossini, A. J.; Vela, J.

Chem. Mater. 2016, 28, 6848-6859. 33. Brivio, F.; Caetano, C.; Walsh, A. J. Phys. Chem. Lett. 2016, 7, 1083-1087. 34. Hoke, E. T.; Slotcavage, D. J.; Dohner, E. R.; Bowring, A. R.; Hemamala, I.; McGehee, M. D. Chem. Sci. 2015, 6, 613. 35. Wu, D.; Yue, S.; Wang, W.; An, T.; Li, G.; Ye, L.; Yip, H. Y.; Wong, P. K. Appl.

Surf. Sci. 2017, 391, 516-524. 36. Fredj, D.; Hassen, C. B.; Elleuch, S.; Feki, H.; Boudjada, N. C.; Mhiri, T.; Boujelbene, M. Mater. Res. Bull. 2017, 85, 23-29. 37. Bastard, G.; Delalande, C.; Meynadier, M. H.; Frijlink, P. M.; Voos, M. Phys. Rev.

B 1984, 29, 7042-7044. 38. Street, R. A.; Mott, N. F. Phys. Rev. Lett. 1975, 35, 1293-1296. 39. Yang, W.; Lowe-Webb, R. R.; Lee, H.; Sercel, P. C. Phys. Rev. B 1997, 56, 13314. 40. Sproul, A. B.; Green, M. A.; Stephens, A. W. J. Appl. Phys. 1992, 72, 4161. 41. Wang, L.; McCleese, C.; Kovalsky, A.; Zhao, Y.; Burda, C. J. Am. Chem. Soc. 2014, 136, 12205-12208. 42. Wang, H.; Yuan, X.; Wu, Y.; Zeng, G.; Tu, W.; Sheng, C.; Deng, Y.; Chen, F.; Chew, J. W. Appl. Catal. B-Environ. 2017, 209, 543-553. 43. Abdelhady, A. L.; Saidaminov, M. I.; Murali, B.; Adinolfi, V.; Voznyy, O.; Katsiev, K.; Alarousu, E.; Comin, R.; Dursun, I.; Sinatra, L.; Sargent, E. H.; Mohammed, O. F.; Bakr, O. M. J. Phys. Chem. Lett. 2016, 7, 295-301. ACS Paragon Plus Environment

Nano Letters 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

44. Jiang, D. S.; Jung, H.; Ploog, K. 1988, 64, 1371. 45. Khatsevich, S.; Rich, D. H.; Zhang, X.; Zhou, W.; Dapkus, P. D. 2004, 95, 1832. 46. Li, D.; Zhang, J.; Xiong, Q. ACS Nano 2012, 6, 5283-5290. 47. Boles, M. A.; Ling, D.; Hyeon, T.; Talapin, D. V. Nat. Mater. 2016, 15, 135-141. 48. Lin, C. C.; Xu, K. Y.; Wang, D.; Meijerink, A. Sci. Rep. 2017, 7, 45906. 49. Van Eijk, C. W. E. Phys. Med. Biol. 2002, 47, R85–R106. 50. Birowosuto, M. D.; Cortecchia, D.; Drozdowski, W.; Brylew, K.; Lachmanski, W.; Bruno, A.; Soci, C. Sci. Rep. 2016, 6, 37254. 51. Leng, M.; Yang, Y.; Zeng, K.; Chen, Z.; Tan, Z.; Li, S.; Li, J.; Xu, B.; Li, D.; Hautzinger, M. P.; Fu, Y.; Zhai, T.; Xu, L.; Niu, G.; Jin, S.; Tang, J. Adv. Funct. Mater. 2017, 28, 1704446. 52. Liu, H.; Wu, Z.; Shao, J.; Yao, D.; Gao, H.; Liu, Y.; Yu, W.; Zhang, H.; Yang, B. 2017, 11, 2239-2247.


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