Blue-Emitting CsPbCl3 Nanocrystals: Impact of Surface Passivation for

Nov 20, 2018 - D.; Friend, R. H.; Song, M. H. Amine-Based Passivating Materials for. Enhanced Optical Properties and Performance of Organic-Inorganic...
1 downloads 0 Views 4MB Size
Download PDF
Letter pubs.acs.org/JPCL

Cite This: J. Phys. Chem. Lett. 2018, 9, 6884−6891

Blue-Emitting CsPbCl3 Nanocrystals: Impact of Surface Passivation for Unprecedented Enhancement and Loss of Optical Emission Rakesh Kumar Behera,§ Samrat Das Adhikari,§ Sumit Kumar Dutta, Anirban Dutta,* and Narayan Pradhan* School of Materials Science, Indian Association for the Cultivation of Science, Kolkata 700032, India

Downloaded via KAOHSIUNG MEDICAL UNIV on November 27, 2018 at 01:19:31 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: High-energy-emitting CsPbCl3 nanocrystals have shown significant loss and enhancement of their emission intensity (∼40−50 folds) during purification and surface treatments, respectively. This confirms that the surfaces of these nanocrystals are very sensitive. In this Letter, physical insights of the interface bindings on the surface of these blue-emitting CsPbCl3 nanocrystals with different passivating agents and their consequential impact on purification are investigated. Using various metal chlorides irrespective of the charge and size of the metal ions, metal acetates, and nonmetal chloride, the predominant influence of chloride ions in helping retrieve/intensify the blue emission is established. The purification processes are observed to be very delicate, and successive purifications with introduction of polar nonsolvents led to the transformation of an emitting cubic CsPbCl3 phase to nonemitting tetragonal CsPb2Cl5 phase nanocrystals irreversibly. The impact of various salt additions only temporarily helped in enhancing the emission, but the phase change remained inevitable upon successive purification. However, as a remedy, by in situ use of alkylammonium chloride salt in high-temperature reactions, the surface binding was improved, and significant emission as well as the phase could be retained with successive purifications.

I

chemistry for stabilizing and preventing interfering defects in these nanocrystals is still elusive, and more investigations are required. For chalcogenide nanocrystals, the role of surface ligands is extensively studied.53−57 Typically, successive purification using a solvent/nonsolvent approach removes the loosely bound ligands and creates surface defect states.55,56 This also leads to agglomeration of nanocrystals though the crystal phase, and the shape of the nanocrystals broadly remains unchanged. However, perovskite nanocrystals are more sensitive to polar solvents. Hence, it is important to know more about the impact of the purification process and whether it is similar to or different than that of chalcogenide nanocrystals. In addition to the proper surface passivating agents, quantitative analysis of the chemical/physical changes of the nanocrystals during purification is critically important for colloidal and optical stability of these nanocrystals. Keeping all of the above issues in mind, herein, we studied the impact of passivating agents on the high-energy-emitting CsPbCl3 nanocrystals, which has shown significant emission intensity loss/enhancement during surface treatment and purification. Randomly using large varieties of metal halides/ acetates and a nonmetal halide source, their role at the interface for retrieving/intensifying the emission was inves-

nterface chemistry of nanocrystals in solution is important for surface modification and processing for various applications.1−5 Among the leading energy materials, recently developed lead halide perovskite nanocrystals, which had shown unprecedented high quantum efficiency,6−21 also suffer the intensity loss because of the vacancies or distorted [PbX6] octahedra.22−24 This has been critically reflected for the highenergy-emitting CsPbCl3 nanocrystals, which showed much less quantum efficiency (QY), typically within 1−5% QY in comparison to the standard 70−80% QY of CsPbBr3.6,9,25−31 Hence, it became important to understand the interface chemistry of these nanocrystals and the role of surface ligands for avoiding the creation of additional interfering nonradiative states or loss of emitting nanocrystals during the purification process. Recent developments suggest that addition of suitable metal halide salts significantly improves the surface capping and enhances the luminescence intensity of cesium lead halide nanocrystals.2,13,15,32 It is also reported that the defect states that are responsible for quenching the original emission are created mostly due to surface halide vacancy.7,15,24,32−36 Hence, it is still unclear what role the metal part plays in the halides and whether these also help retrieve the emission. Further, it is established that alkylammonium ions typically bind on the surface of these nanocrystals via hydrogen bonding with surface halides.2,8,23,26,37−40 Apart from these, some other additives and dopants were also reported that helped in retaining/enhancing emission.18,22,33,41−52 Hence, the interface © XXXX American Chemical Society

Received: October 3, 2018 Accepted: November 20, 2018

6884

DOI: 10.1021/acs.jpclett.8b03047 J. Phys. Chem. Lett. 2018, 9, 6884−6891

Letter

The Journal of Physical Chemistry Letters

Figure 1. Photoluminescence (PL) spectra of CsPbCl3 nanocrystals after one round of purification using a 1:2 volume ratio of hexane and ethyl acetate (black spectral line) and after addition of a metal chloride (1:1 ratio of Pb to other metal/ammonium) stock solution (blue spectral line). The excitation wavelength for all cases was 350 nm. RNH3Cl refers to oleylammonium chloride. The measurement was performed taking the fixed volume of the nanocrystal solution in hexane, and then, the salt solution was added directly into the cuvette at room temperature.

Figure 2. (a) Colloidal stability in terms of the PLQY of CsPbCl3 nanocrystals in untreated and oleylammonium chloride- and SnCl4-treated samples measured for 7 days. (b) Metal halide concentration-dependent PLQY change of the CsPbCl3 nanocrystals. (Inset) Digital picture of the cuvettes containing salt (SnCl4)-treated (left) and untreated (right) CsPbCl3 nanocrystal solutions under UV light (λex = 365 nm).

1:2 of hexane to ethyl acetate was used throughout purification. After the first round of purification, these nanocrystals were dispersed in hexane, and different metal chloride salt stock solutions were added to the fixed volume of the dispersed nanocrystals, maintaining a Pb to metal 1:1 ratio (see experimental details in the Supporting Information). Interestingly, for all metal salts Sb(III), Bi(III), V(III), Ni(II), Zn(II), Sn(II), Sn(IV), Pb(II), and Cu(I) chlorides, the emission intensity was observed to increase (see Figure 1). Even though it varied from one to another metal chloride salt, the standard enhancement remained within 10−50 times the original emission. An important aspect of the enhanced emission is their colloidal as well as photostability. These were studied for oleylammonium chloride and SnCl4 and compared with untreated nanocrystals after the first round of purification. The colloidal stability for these nanostructures, shown in Figure 2a, showed that the intensity remained almost unchanged for 7 days. Similarly, the photostability under irradiation at 365 nm (4 w) also confirmed that these were stable (Figure S1). Hence, in dispersed solution, these nanostructures after post salt treatment were observed to be

tigated. With repeated purifications using an ideal combination of solvent/nonsolvent, their impact on the emission loss and shape/size/phase changes was studied. While successive purification was found to drastically change the crystal phase of emitting cubic CsPbCl3 to nonemitting tetragonal CsPb2Cl5, surface retreatment with passivating chloride salts retrieved the emission only from the cubic phase nanocrystals and had no impact on the tetragonal phase. As a remedy, alkyl ammonium halides were used during the synthesis process, which served as a dual passivating agent for supplying the halide ions as well as ammonium ions and provided significant stability toward the optical emission and resistivity toward successive purification for preventing crystal phase and shape change of the nanocrystals. To observe the emission stability, CsPbCl3 nanocrystals were synthesized following a modified literature method and purified with hexane and ethyl acetate as the solvent and nonsolvent, respectively.6 Ethyl acetate was chosen because of its relatively low polarity in comparison to acetone and tbutanol, which were also used as nonsolvents during perovskite nanocrystal purifications.6,58,59 The standard volume ratio of 6885

DOI: 10.1021/acs.jpclett.8b03047 J. Phys. Chem. Lett. 2018, 9, 6884−6891

Letter

The Journal of Physical Chemistry Letters

Figure 3. (a) Absorption and (b) successive PL spectra of as-synthesized CsPbCl3 perovskite nanocrystals and after successive purification. W0 is the crude sample collected and directly dispersed in hexane, and W1−W4 stand for the samples dispersed in hexane after 1−4 rounds of purification using 1:2 volume ratios of hexane and ethyl acetate. (c) Powder XRD patterns of the samples collected after several rounds of purification. (d,e) TEM and HRETM images of the nanostructures obtained from the first round of purification (W1), respectively. (f,g) TEM and HRTEM images of sheet-like structures obtained after the fourth round of purification (W4). (Inset) Selected-area FFT of corresponding HRTEM images.

shows the absorption and PL spectra of the perovskite nanocrystals with successive purifications using a 1:2 volume ratio of hexane and ethyl acetate, respectively. While the absorption spectra were observed to gradually become flat, the emission intensity was seen to be drastically reduced and almost completely quenched after four rounds of purifications. Figure 3c shows the successive powder X-ray diffraction (XRD) patterns of the samples after each step of purification. From the peak positions, it was revealed that the initial cubic phase of the CsPbCl3 nanocrystals slowly changed to the tetragonal phase of CsPb2Cl5. Figure 3d,e presents transmission electron microscope (TEM) and high-resolution TEM (HRTEM) images of the sample obtained after the first round of purification (W1), which showed the cube shape of the nanostructures. From the fast Fourier transform (FFT) of a selected area of the HRTEM, the cubic phase was also confirmed for these nanostructures. Figure 3f,g presents the TEM and HRTEM images of the sample collected after the fourth round of purification (W4), respectively. These were observed to be sheet-like structures, and from the HRTEM analysis, the phase was confirmed to be tetragonal, which was viewed along the z-direction. From these images, it became clear that the original cube-shaped CsPbCl3 nanocrystals were diminished significantly and sheet-like structures were formed. TEM images of the intermediate stage samples were also viewed, which showed a mixture of cube and sheet-like structures (Figure S6). However, the transformation mechanism could not be correlated here between these two shapes of the nanostructures as they bear different coordination environments for lead.26 Because the tetragonal CsPb2Cl5 is a nonemitting phase and sheets were formed during purification, the emission was quenched. Hence, it could be concluded here that purification of the CsPbCl3 nanocrystals remained sensitive and that these could transform permanently to a different nonemitting phase of nanocrystals.

stable under our measurement conditions. However, no emission enhancement was observed for the corresponding metal acetate salts (Figure S2). The variation of PL intensity from one to another salt was attributed to the different ability of different metal salts to release active chloride to the solution. To further understand this, ZnCl2 and BiCl3 salts were specifically chosen as they have a smaller increment of emission, while when more salts were added sequentially the PL intensities were also observed to be enhanced. Figure 2b shows the metal chloride salt concentration-dependent photoluminescence quantum yield (PLQY) enhancement, and the results support that the active chloride ion release mostly controlled the extent of enhancement of the emission intensities. To understand the origin of the emission enhancement, the experiment was also carried out with nonmetal chloride salt. Oleylammonium chloride was selected as a nonmetal halide source, and also significant enhancement of the PL intensity was observed (Figure 1). Hence, it could be stated here that chloride ions played a major role for surface passivation and retrieving/enhancing the optical emission. However, the enhanced emission due to treatment of these chloride salts was further reduced upon purification. As polar nonsolvents affect the optical properties of the nanostructures,41,58−61 the change in the optical properties and crystal phase of CsPbCl3 nanocrystals was first studied with several rounds of purifications. Acetone and t-butanol, which were previously used as nonsolvent for purification of the perovskite nanocrystals, were observed to drastically reduce the optical properties of the CsPbCl3 nanocrystals upon repeated purification (Figures S3 and S4). The origin of the emission reduction was due to a change in the crystal phase of the emitting cubic CsPbCl3 to nonemitting tetragonal CsPb2Cl5 (Figure S5). When ethyl acetate was chosen as a relatively low polar nonsolvent for purification, the change became less pronounced. Figure 3a,b 6886

DOI: 10.1021/acs.jpclett.8b03047 J. Phys. Chem. Lett. 2018, 9, 6884−6891

Letter

The Journal of Physical Chemistry Letters

Figure 4. (a) Absorption spectra and (b) corresponding PL spectra of CsPbCl3 nanocrystals with successive purifications and addition of oleylammonium salts. W0 stands for the crude sample and W1−W3 the number of purification steps, and W+S is the purification step followed by salt addition. (c) Plot of step experiments versus PLQY. The excitation wavelength is 350 nm.

Figure 5. (a) Absorption and (b) corresponding PL spectra of the nanocrystals obtained with successive purification processes, which were prepared by adding preformed oleylammonium chloride salt at the beginning of the reaction. (c) Successive powder XRD patterns of the products obtained from successive purification processes. (d,e) TEM images of the samples obtained after purification steps 1 and 4, respectively.

the UV−visible absorbance and PL spectra of the nanocrystals obtained after successive purifications and subsequent additions of oleylammonium chloride salt. Figure 4c presents the concerned experiments versus the quantum yield of the nanocrystals. It became clear from the observation that the PL intensity was retrieved in each step, but the extents were gradually decreased, and finally the PL spectra were grounded. However, TEM images obtained from different steps of this purification and addition of salt are shown in Figure S8, and importantly, here the cubes were seen to change to platelets

Because the CsPbCl3 nanocrystals showed enhanced or retrieved emission upon addition of any halide salt after the first wash (Figure 1), it is important to know whether these enhanced emissions became stable or again were quenched with further purification. Figure S7 presents the PL spectra of the successively washed samples after salt treatment. Upon purification, the emission intensity gradually decreased, suggesting that the PL enhancement was not permanent. Further, to check the effectiveness of the salt treatment, salts were added after each step of purification. Figure 4a,b shows 6887

DOI: 10.1021/acs.jpclett.8b03047 J. Phys. Chem. Lett. 2018, 9, 6884−6891

Letter

The Journal of Physical Chemistry Letters

Figure 6. (a) Atomic model showing CsPbCl3 nanocrystals in equilibrium with alkylammonium and chloride ions. An excess of chloride ions improves the PL intensity. (b) Atomic models showing the phase change of cubic CsPbCl3 to tetragonal CsPb2Cl5 during the purification process.

and finally to sheets of tetragonal phase, as expected (XRD shown in Figure S8d). Apart from oleylammonium chloride salt, similar experiments were also carried out for the metal salts. Two such cases using ZnCl2 and SnCl4 addition followed by purifications were carried out, and similar results were also obtained (Figure S9), confirming that the nanocrystals with salt added in solution also undergo phase change in the presence of polar solvents used during the purification process. From all of the above results, apparently, it became clear that these nanocrystals were not stable during the purification process, and hence, this created doubt for retaining their stability under vigorous purification processes using the polar solvent. To further verify the stability of the nanocrystals, the nanocrystals were prepared following our previously reported method with in situ addition of alkylammonium chloride salt as a dual passivating agent.8,9,26 Figure 5a,b shows the UV−visible absorbance and PL spectra of the nanocrystals obtained after successive purification steps. Interestingly, it was observed that under similar purification conditions (as in Figure 3) these nanocrystals retained significant emission even after the fourth round of purification. Powder XRD patterns obtained from samples collected after successive purification are shown in Figure 5c. From the optical spectra and powder XRD patterns, it became evident that the emission loss and phase change were much slower in comparison to previous observations, and significant emission also remained after the fourth step of purification. TEM images show only cubes at the initial stage, but sheets were formed after the fourth round of purification, though dominated by cubes (Figures 5d,e and S10). Comparing all the above results, it could be concluded that in situ salt-treated reactions showed a temporary solution and surface resistivity against successive purification steps. From all of the above results, it could be stated here that in dispersed solution CsPbCl3 nanocrystals maintain equilibrium with chloride ions and the alkylammonium ions used for capping the nanocrystals. Chloride ions played a major role for retaining or retrieving the emission as the defect states mostly arise from the halide vacancy. During purification, the free ions in the bulk solution were reduced, and hence, the capping ions or surface ions were dispersed to the bulk solution, and this quenched the emission and also facilitated the phase transformation. However, using alkylammonium chloride salt in in situ reactions helped in binding the ammonium ions firmly8,9,26 and also helped the chloride ions tagged for the charge balance.2 As a result, these nanocrystals showed better resistivity for phase change during the purification process. Accordingly, a schematic model is shown in Figure 6a where

free ions are shown in equilibrium with the surface ions/ ligands of CsPbCl3 nanocrystals, and to retain a high PLQY, the presence of free chloride and ammonium ions is essentially required to be in the bulk solution. Figure 6b presents a schematic atomic model of phase change from the cubic to tetragonal phase during purification steps. The loss of ammonium ions was further verified by nuclear magnetic resonance (NMR) spectra of the samples. The NMR spectra of the first and fourth step purified sample are presented in Figure S11. It was clearly observed that the ammonium ion peak at 7.2 ppm diminished during purification.8,9,26 Hence, the presence of ammonium ion is essential for preserving the cubic phase of the nanocrystals. Not only for CsPbCl3, the successive purification process was also studied for CsPbBr3 nanocrystals (Figure S12 UV− vis, PL, XRD, and TEM), and importantly, these nanocrystals showed better stability, and intense emission was also seen after the fourth round of purification, though similar phase and shape changes were also observed in this case. Being that the CsPbCl3 system is less studied and widely reported for low QY, the entire study here remained focused for understanding the surface chemistry of these high-energy-emitting nanocrystals. In conclusion, the surface sensitivity of the high-energyemitting CsPbCl3 nanocrystals was studied, which showed an enhancement and loss of nearly 50-fold of emission intensities with the addition of proper passivators during synthesis and purifications, respectively. This also confirmed that these nanocrystals created interfering surface defect states that trigger nonradiative emission and reduced the overall quantum efficiency. Further, different cycles of purifications were carried out where the emission quenching as well as the simultaneous phase change in successive steps was reported. This further confirmed that for any amount of polar solvent the original emission was affected as the cubic phase of nanocrystals slowly diminished and nonemitting tetragonal phase nanocrystals were formed. However, using ammonium chloride salts in high-temperature reactions, a significant amount of emission intensity could be retained even after several purification processes. The entire study indeed concluded that for perovskite nanocrystals and particularly for high-energyemitting CsPbCl3 the surfaces are indeed very sensitive, which simultaneously leads to (a) creation of interfering states as well as (b) phase changes, and much more effort is required to retain the original emission of these nanocrystals during the purification process, which are the key steps for any kind of processing for their applications. Further, this oleylammonium chloride salt provided a temporary solution, but certainly, this 6888

DOI: 10.1021/acs.jpclett.8b03047 J. Phys. Chem. Lett. 2018, 9, 6884−6891

Letter

The Journal of Physical Chemistry Letters

(10) Saidaminov, M. I.; Mohammed, O. F.; Bakr, O. M. LowDimensional-Networked Metal Halide Perovskites: The Next Big Thing. ACS Energy Lett. 2017, 2, 889−896. (11) Kumar, S.; Jagielski, J.; Yakunin, S.; Rice, P.; Chiu, Y.-C.; Wang, M.; Nedelcu, G.; Kim, Y.; Lin, S.; Santos, E. J. G.; et al. Efficient Blue Electroluminescence Using Quantum-Confined Two-Dimensional Perovskites. ACS Nano 2016, 10, 9720−9729. (12) Manser, J. S.; Saidaminov, M. I.; Christians, J. A.; Bakr, O. M.; Kamat, P. V. Making and Breaking of Lead Halide Perovskites. Acc. Chem. Res. 2016, 49, 330−338. (13) Bohn, B. J.; Tong, Y.; Gramlich, M.; Lai, M. L.; Doeblinger, M.; Wang, K.; Hoye, R. L. Z.; Mueller-Buschbaum, P.; Stranks, S. D.; Urban, A. S.; et al. Boosting Tunable Blue Luminescence of Halide Perovskite Nanoplatelets through Postsynthetic Surface Trap Repair. Nano Lett. 2018, 18, 5231−5238. (14) Zhang, F.; Zhong, H.; Chen, C.; Wu, X.-g.; Hu, X.; Huang, H.; Han, J.; Zou, B.; Dong, Y. Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology. ACS Nano 2015, 9, 4533−4542. (15) Wu, Y.; Wei, C.; Li, X.; Li, Y.; Qiu, S.; Shen, W.; Cai, B.; Sun, Z.; Yang, D.; Deng, Z.; et al. In Situ Passivation of PbBr64‑ Octahedra toward Blue Luminescent CsPbBr3 Nanoplatelets with Near 100% Absolute Quantum Yield. ACS Energy Lett. 2018, 3, 2030−2037. (16) Woo, J. Y.; Kim, Y.; Bae, J.; Kim, T. G.; Kim, J. W.; Lee, D. C.; Jeong, S. Highly Stable Cesium Lead Halide Perovskite Nanocrystals through in situ Lead Halide Inorganic Passivation. Chem. Mater. 2017, 29, 7088−7092. (17) Pan, J.; Shang, Y.; Yin, J.; De Bastiani, M.; Peng, W.; Dursun, I.; Sinatra, L.; El-Zohry, A. M.; Hedhili, M. N.; Emwas, A.-H.; et al. Bidentate Ligand-Passivated CsPbI3 Perovskite Nanocrystals for Stable Near-Unity Photoluminescence Quantum Yield and Efficient Red Light-Emitting Diodes. J. Am. Chem. Soc. 2018, 140, 562−565. (18) Lee, S.; Park, J. H.; Lee, B. R.; Jung, E. D.; Yu, J. C.; Di Nuzzo, D.; Friend, R. H.; Song, M. H. Amine-Based Passivating Materials for Enhanced Optical Properties and Performance of Organic-Inorganic Perovskites in Light-Emitting Diodes. J. Phys. Chem. Lett. 2017, 8, 1784−1792. (19) Akkerman, Q. A.; Raino, G.; Kovalenko, M. V.; Manna, L. Genesis, Challenges and Opportunities for Colloidal Lead Halide Perovskite Nanocrystals. Nat. Mater. 2018, 17, 394−405. (20) Wu, L.; Hu, H.; Xu, Y.; Jiang, S.; Chen, M.; Zhong, Q.; Yang, D.; Liu, Q.; Zhao, Y.; Sun, B.; et al. From Nonluminescent Cs4PbX6 (X = Cl, Br, I) Nanocrystals to Highly Luminescent CsPbX3 Nanocrystals: Water-Triggered Transformation through a CsXStripping Mechanism. Nano Lett. 2017, 17, 5799−5804. (21) Zhang, Q.; Yin, Y. All-Inorganic Metal Halide Perovskite Nanocrystals: Opportunities and Challenges. ACS Cent. Sci. 2018, 4, 668−679. (22) Huang, H.; Lin, H.; Kershaw, S. V.; Susha, A. S.; Choy, W. C. H.; Rogach, A. L. Polyhedral Oligomeric Silsesquioxane Enhances the Brightness of Perovskite Nanocrystal-Based Green Light-Emitting Devices. J. Phys. Chem. Lett. 2016, 7, 4398−4404. (23) Milosavljevic, A. R.; Bozanic, D. K.; Sadhu, S.; Vukmirovic, N.; Dojcilovic, R.; Sapkota, P.; Huang, W.; Bozek, J.; Nicolas, C.; Nahon, L.; Ptasinska, S. Electronic Properties of Free-Standing SurfactantCapped Lead Halide Perovskite Nanocrystals Isolated in Vacuo. J. Phys. Chem. Lett. 2018, 9, 3604−3611. (24) Huang, H.; Bodnarchuk, M. I.; Kershaw, S. V.; Kovalenko, M. V.; Rogach, A. L. Lead Halide Perovskite Nanocrystals in the Research Spotlight: Stability and Defect Tolerance. ACS Energy Lett. 2017, 2, 2071−2083. (25) Kim, Y.; Yassitepe, E.; Voznyy, O.; Comin, R.; Walters, G.; Gong, X.; Kanjanaboos, P.; Nogueira, A. F.; Sargent, E. H. Efficient Luminescence from Perovskite Quantum Dot Solids. ACS Appl. Mater. Interfaces 2015, 7, 25007−25013. (26) Dutta, A.; Behera, R. K.; Dutta, S. K.; Das Adhikari, S.; Pradhan, N. Annealing CsPbX3 (X = Cl and Br) Perovskite Nanocrystals at High Reaction Temperatures: Phase Change and Its Prevention. J. Phys. Chem. Lett. 2018, 9, 6599−6604.

needs more strong surface binding agents to prevent their optical loss during purification and subsequent applications.

■

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpclett.8b03047.

■

Additional TEM images, optical spectra, and experimental details (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (N.P.). *E-mail: [email protected] (A.D.). ORCID

Sumit Kumar Dutta: 0000-0002-9228-1916 Anirban Dutta: 0000-0001-9915-6985 Narayan Pradhan: 0000-0003-4646-8488 Author Contributions §

R.K.B. and S.D.A. have equal contribution.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by DST, Govt. of India (SERB/F/ 7159/2016-17) for funding; R.K.B., S.D.A., A.D., and S.K.D. acknowledge CSIR for fellowships.

■

REFERENCES

(1) Michalet, X.; Pinaud, F. F.; Bentolila, L. A.; Tsay, J. M.; Doose, S.; Li, J. J.; Sundaresan, G.; Wu, A. M.; Gambhir, S. S.; Weiss, S. Quantum Dots for Live Cells, in Vivo Imaging, and Diagnostics. Science 2005, 307, 538−544. (2) Pan, J.; Quan, L. N.; Zhao, Y.; Peng, W.; Murali, B.; Sarmah, S. P.; Yuan, M.; Sinatra, L.; Alyami, N. M.; Liu, J.; et al. Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering. Adv. Mater. 2016, 28, 8718−8725. (3) Owen, J. S.; Park, J.; Trudeau, P.-E.; Alivisatos, A. P. Reaction Chemistry and Ligand Exchange at Cadmium-Selenide Nanocrystal Surfaces. J. Am. Chem. Soc. 2008, 130, 12279−12281. (4) El-Sayed, M. A. Small is different: Shape-, Size-, and Composition-dependent Properties of Some Colloidal Semiconductor Nanocrystals. Acc. Chem. Res. 2004, 37, 326−333. (5) Chen, B.; Pradhan, N.; Zhong, H. From Large-Scale Synthesis to Lighting Device Applications of Ternary I-III-VI Semiconductor Nanocrystals: Inspiring Greener Material Emitters. J. Phys. Chem. Lett. 2018, 9, 435−445. (6) Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.; Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V. Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut. Nano Lett. 2015, 15, 3692−3696. (7) Kovalenko, M. V.; Protesescu, L.; Bodnarchuk, M. I. Properties and Potential Optoelectronic Applications of Lead Halide Perovskite Nanocrystals. Science 2017, 358, 745−750. (8) Dutta, A.; Dutta, S. K.; Das Adhikari, S.; Pradhan, N. PhaseStable CsPbI3 Nanocrystals: The Reaction Temperature Matters. Angew. Chem., Int. Ed. 2018, 57, 9083−9087. (9) Dutta, A.; Dutta, S. K.; Das Adhikari, S.; Pradhan, N. Tuning the Size of CsPbBr3 Nanocrystals: All at One Constant Temperature. ACS Energy Lett. 2018, 3, 329−334. 6889

DOI: 10.1021/acs.jpclett.8b03047 J. Phys. Chem. Lett. 2018, 9, 6884−6891

Letter

The Journal of Physical Chemistry Letters (27) Liu, W.; Lin, Q.; Li, H.; Wu, K.; Robel, I.; Pietryga, J. M.; Klimov, V. I. Mn2+-Doped Lead Halide Perovskite Nanocrystals with Dual-Color Emission Controlled by Halide Content. J. Am. Chem. Soc. 2016, 138, 14954−14961. (28) Parobek, D.; Roman, B. J.; Dong, Y.; Jin, H.; Lee, E.; Sheldon, M.; Son, D. H. Exciton-to-dopant Energy Transfer in Mn-doped Cesium Lead Halide Perovskite Nanocrystals. Nano Lett. 2016, 16, 7376−7380. (29) Zhu, J.; Yang, X.; Zhu, Y.; Wang, Y.; Cai, J.; Shen, J.; Sun, L.; Li, C. Room-Temperature Synthesis of Mn-Doped Cesium Lead Halide Quantum Dots with High Mn Substitution Ratio. J. Phys. Chem. Lett. 2017, 8, 4167−4171. (30) Peng, L.; Dutta, A.; Xie, R.; Yang, W.; Pradhan, N. Dot-WirePlatelet-Cube: Step Growth and Structural Transformations in CsPbBr3 Perovskite Nanocrystals. ACS Energy Lett. 2018, 3, 2014− 2020. (31) Tong, Y.; Bohn, B. J.; Bladt, E.; Wang, K.; Mueller-Buschbaum, P.; Bals, S.; Urban, A. S.; Polavarapu, L.; Feldmann, J. From Precursor Powders to CsPbX3 Perovskite Nanowires: One-Pot Synthesis, Growth Mechanism, and Oriented Self-Assembly. Angew. Chem., Int. Ed. 2017, 56, 13887−13892. (32) Ahmed, G. H.; El-Demellawi, J. K.; Yin, J.; Pan, J.; Velusamy, D. B.; Hedhili, M. N.; Alarousu, E.; Bakr, O. M.; Alshareef, H. N.; Mohammed, O. F. Giant Photoluminescence Enhancement in CsPbCl3 Perovskite Nanocrystals by Simultaneous Dual-Surface Passivation. ACS Energy Lett. 2018, 3, 2301−2307. (33) Koscher, B. A.; Swabeck, J. K.; Bronstein, N. D.; Alivisatos, A. P. Essentially Trap-Free CsPbBr3 Colloidal Nanocrystals by Postsynthetic Thiocyanate Surface Treatment. J. Am. Chem. Soc. 2017, 139, 6566−6569. (34) Liu, Y.; Xiao, H.; Goddard, W. A. Two-Dimensional Halide Perovskites: Tuning Electronic Activities of Defects. Nano Lett. 2016, 16, 3335−3340. (35) Kang, J.; Wang, L.-W. High Defect Tolerance in Lead Halide Perovskite CsPbBr3. J. Phys. Chem. Lett. 2017, 8, 489−493. (36) Manser, J. S.; Christians, J. A.; Kamat, P. V. Intriguing Optoelectronic Properties of Metal Halide Perovskites. Chem. Rev. 2016, 116, 12956−13008. (37) Ravi, V. K.; Santra, P. K.; Joshi, N.; Chugh, J.; Singh, S. K.; Rensmo, H.; Ghosh, P.; Nag, A. Origin of the Substitution Mechanism for the Binding of Organic Ligands on the Surface of CsPbBr3 Perovskite Nanocubes. J. Phys. Chem. Lett. 2017, 8, 4988− 4994. (38) De Roo, J.; Ibanez, M.; Geiregat, P.; Nedelcu, G.; Walravens, W.; Maes, J.; Martins, J. C.; Van Driessche, I.; Kovalenko, M. V.; Hens, Z. Highly Dynamic Ligand Binding and Light Absorption Coefficient of Cesium Lead Bromide Perovskite Nanocrystals. ACS Nano 2016, 10, 2071−2081. (39) Pan, A.; He, B.; Fan, X.; Liu, Z.; Urban, J. J.; Alivisatos, A. P.; He, L.; Liu, Y. Insight into the Ligand-Mediated Synthesis of Colloidal CsPbBr3 Perovskite Nanocrystals: The Role of Organic Acid, Base, and Cesium Precursors. ACS Nano 2016, 10, 7943−7954. (40) Imran, M.; Caligiuri, V.; Wang, M.; Goldoni, L.; Prato, M.; Krahne, R.; De Trizio, L.; Manna, L. Benzoyl Halides as Alternative Precursors for the Colloidal Synthesis of Lead-Based Halide Perovskite Nanocrystals. J. Am. Chem. Soc. 2018, 140, 2656−2664. (41) Wang, H.; Sui, N.; Bai, X.; Zhang, Y.; Rice, Q.; Seo, F. J.; Zhang, Q.; Colvin, V. L.; Yu, W. W. Emission Recovery and Stability Enhancement of Inorganic Perovskite Quantum Dots. J. Phys. Chem. Lett. 2018, 9, 4166−4173. (42) Li, Q.-L.; Lu, W.-X.; Ding, S.-N.; Wan, N. Tuning Optical Properties of Perovskite Nanocrystals by Supermolecular Mercapto-βcyclodextrin. Chem. Commun. 2016, 52, 12342−12345. (43) Wang, C.; Chesman, A. S. R.; Jasieniak, J. J. Stabilizing the Cubic Perovskite Phase of CsPbI3 Nanocrystals by using an Alkyl Phosphinic Acid. Chem. Commun. 2017, 53, 232−235. (44) Veldhuis, S. A.; Ng, Y. F.; Ahmad, R.; Bruno, A.; Jamaludin, N. F.; Damodaran, B.; Mathews, N.; Mhaisalkar, S. G. Crown Ethers

Enable Room-Temperature Synthesis of CsPbBr3 Quantum Dots for Light-Emitting Diodes. ACS Energy Lett. 2018, 3, 526−531. (45) Hou, S.; Guo, Y.; Tang, Y.; Quan, Q. Synthesis and Stabilization of Colloidal Perovskite Nanocrystals by Multidentate Polymer Micelles. ACS Appl. Mater. Interfaces 2017, 9, 18417−18422. (46) Meyns, M.; Peralvarez, M.; Heuer-Jungemann, A.; Hertog, W.; Ibanez, M.; Nafria, R.; Genc, A.; Arbiol, J.; Kovalenko, M. V.; Carreras, J.; et al. Polymer-Enhanced Stability of Inorganic Perovskite Nanocrystals and Their Application in Color Conversion LEDs. ACS Appl. Mater. Interfaces 2016, 8, 19579−19586. (47) Raja, S. N.; Bekenstein, Y.; Koc, M. A.; Fischer, S.; Zhang, D.; Lin, L.; Ritchie, R. O.; Yang, P.; Alivisatos, A. P. Encapsulation of Perovskite Nanocrystals into Macroscale Polymer Matrices: Enhanced Stability and Polarization. ACS Appl. Mater. Interfaces 2016, 8, 35523−35533. (48) Zhou, Q.; Bai, Z.; Lu, W.-g.; Wang, Y.; Zou, B.; Zhong, H. In Situ Fabrication of Halide Perovskite Nanocrystal-Embedded Polymer Composite Films with Enhanced Photoluminescence for Display Backlights. Adv. Mater. 2016, 28, 9163−9168. (49) Huang, H.; Chen, B.; Wang, Z.; Hung, T. F.; Susha, A. S.; Zhong, H.; Rogach, A. L. Water Resistant CsPbX3 Nanocrystals Coated with Polyhedral Oligomeric Silsesquioxane and their use as Solid State Luminophores in All-perovskite White Light-emitting Devices. Chem. Sci. 2016, 7, 5699−5703. (50) Zhang, X.; Lin, H.; Huang, H.; Reckmeier, C.; Zhang, Y.; Choy, W. C. H.; Rogach, A. L. Enhancing the Brightness of Cesium Lead Halide Perovskite Nanocrystal Based Green Light-Emitting Devices through the Interface Engineering with Perfluorinated Ionomer. Nano Lett. 2016, 16, 1415−1420. (51) Ahmed, T.; Seth, S.; Samanta, A. Boosting the Photoluminescence of CsPbX3 (X = Cl, Br, I) Perovskite Nanocrystals Covering a Wide Wavelength Range by Postsynthetic Treatment with Tetrafluoroborate Salts. Chem. Mater. 2018, 30, 3633−3637. (52) Yong, Z.-J.; Ma, J.-P.; Li, Z.-Y.; Chen, Y.-M.; Zhang, B.-B.; Zhou, Y.; Sun, H.-T.; Guo, S.-Q.; Zhang, J.-Y.; et al. DopingEnhanced Short-Range Order of Perovskite Nanocrystals for NearUnity Violet Luminescence Quantum Yield. J. Am. Chem. Soc. 2018, 140, 9942−9951. (53) Sarkar, S.; Patra, B. K.; Guria, A. K.; Pradhan, N. The Redox Chemistry at the Interface for Retrieving and Brightening the Emission of Doped Semiconductor Nanocrystals. J. Phys. Chem. Lett. 2013, 4, 2084−2090. (54) Arora, V.; Soni, U.; Mittal, M.; Yadav, S.; Sapra, S. Synthesis of Trap Emission Free Cadmium Sulfide Quantum Dots: Role of Phosphonic Acids and Halide ions. J. Colloid Interface Sci. 2017, 491, 329−335. (55) von Holt, B.; Kudera, S.; Weiss, A.; Schrader, T. E.; Manna, L.; Parak, W. J.; Braun, M. Ligand Exchange of CdSe Nanocrystals Probed by Optical Spectroscopy in the Visible and Mid-IR. J. Mater. Chem. 2008, 18, 2728−2732. (56) Kalyuzhny, G.; Murray, R. W. Ligand Effects on Optical Properties of CdSe Nanocrystals. J. Phys. Chem. B 2005, 109, 7012− 7021. (57) Liu, J.; Yang, W.; Li, Y.; Fan, L.; Li, Y. Electrochemical Studies of the Effects of the Size, Ligand and Composition on the Band Structures of CdSe, CdTe and their Alloy Nanocrystals. Phys. Chem. Chem. Phys. 2014, 16, 4778−4788. (58) Hoshi, K.; Chiba, T.; Sato, J.; Hayashi, Y.; Takahashi, Y.; Ebe, H.; Ohisa, S.; Kido, J. Purification of Perovskite Quantum Dots Using Low-Dielectric-Constant Washing Solvent ″Diglyme″ for Highly Efficient Light-Emitting Devices. ACS Appl. Mater. Interfaces 2018, 10, 24607−24612. (59) Das Adhikari, S.; Dutta, S. K.; Dutta, A.; Guria, A. K.; Pradhan, N. Chemically Tailoring the Dopant Emission in Manganese-Doped CsPbCl3 Perovskite Nanocrystals. Angew. Chem., Int. Ed. 2017, 56, 8746−8750. (60) Fang, F.; Chen, W.; Li, Y.; Liu, H.; Mei, M.; Zhang, R.; Hao, J.; Mikita, M.; Cao, W.; Pan, R.; et al. Employing Polar Solvent Controlled Ionization in Precursors for Synthesis of High-Quality 6890

DOI: 10.1021/acs.jpclett.8b03047 J. Phys. Chem. Lett. 2018, 9, 6884−6891

Letter

The Journal of Physical Chemistry Letters Inorganic Perovskite Nanocrystals at Room Temperature. Adv. Funct. Mater. 2018, 28, 1706000−1706009. (61) Sun, J.-K.; Huang, S.; Liu, X.-Z.; Xu, Q.; Zhang, Q.-H.; Jiang, W.-J.; Xue, D.-J.; Xu, J.-C.; Ma, J.-Y.; Ding, J.; et al. Polar Solvent Induced Lattice Distortion of Cubic CsPbI3 Nanocubes and Hierarchical Self-Assembly into Orthorhombic Single-Crystalline Nanowires. J. Am. Chem. Soc. 2018, 140, 11705−11715.

6891

DOI: 10.1021/acs.jpclett.8b03047 J. Phys. Chem. Lett. 2018, 9, 6884−6891