X = Cl, Br, I - American Chemical Society

Dec 7, 2017 - Indian Institute of Science Education and Research (IISER),. Pune 411008, India. □ AUTHOR INFORMATION. Corresponding Authors. *E-mails...
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Can B‑Site Doping or Alloying Improve Thermal- and Phase-Stability of All-Inorganic CsPbX3 (X = Cl, Br, I) Perovskites?

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ntentional incorporation of impurity ions into the crystal lattice is termed doping and has been used as an important strategy to tailor electronic, optical, and magnetic properties of a material.1 Therefore, the major aim of doping (or even alloying) is to impart new functionalities into the host material. In contrast, the present discussion is on whether the doping can increase the stability of the host without altering its optoelectronic properties. The specific question is, can partial substitution of Pb2+ with other metal ions (from an extent of doping to alloying) stabilize the desired phase of CsPbX3 (X = Cl, Br, I) perovskites for commercially viable optoelectronic applications? Metal halide perovskites having generic formula ABX3, where A-site cations comprise MA+ (CH3NH3+), FA+ ([(NH2)2CH]+), and Cs+ and the B-site is mostly Pb2+ because other ions like Sn2+ and Ge2+ get easily oxidized to the +4 state. The most celebrated compounds in this category are organic− inorganic hybrid perovskites such as MAPbI3 and FAPbI3, forming solar cells with high (>22%) power conversion efficiency (PCE).2 However, such hybrids suffer from poor thermal stability owing to the volatile organic A-site cation.3 A probable solution to this problem can be replacement of the organic cation with inorganic Cs+.4 However, this replacement creates a new problem, where the black-colored cubic (α-) phase of CsPbI 3 (required for solar cell and other optoelectronic applications) is not stable at room temperature.5,6 Therefore, many optimizations are being attempted with organic−inorganic mixed A-site cations to improve the thermal stability of APbI3 perovskite.7−9 In another approach, α-CsPbI3 can be stabilized by partially replacing the I− with smaller sized Br− forming CsPb(Br+I)3.10 However, Br− incorporation increases the band gap, which is detrimental for solar cell efficiency.11 Furthermore, newer strategies such as making nanocrystals (NCs) are also reported to stabilize the cubic phase of CsPbI3, but decrease in crystallite size inhibits charge transport.6,12,13 Interestingly, a recent report on CsPbI3 NC-based solar cells shows a high (13.4%) PCE after better optimization of the film deposition and surface chemistry of NCs, improving the charge transport in NC films.14 Overall, there are various approaches for improving the thermal and structural stability of APbI3 perovskites, but the problem is not yet solved to a satisfactory level. Therefore, a new strategy has been discussed for about the last year, in which partial substitution of Pb2+ (B-site cation) with different metal ions has been suggested as a possible way to improve both the thermal and phase stability of ABX3 perovskites (Figure 1).15−21 Herein, we will discuss the potential of partial substitution of B-site cations in stabilizing the metal halide perovskite structure. Previous studies suggest that the formation energy of the Bsite is larger; therefore, partial substitution of the B-site cation is © XXXX American Chemical Society

Figure 1. Schematic representation showing partial substitution (doping or alloying) of Pb2+ by various metal ions, which can lead to (a) stabilization of α-CsPbI3 at room temperature by increasing the tolerance factor and (b) improved thermal stability of orthorhombic CsPbBr3 by increasing the formation energy.

more difficult compared to that of A-site and X-site cations.22 Also, complete substitution of Pb2+ often results in less impressive optoelectronic properties.23−26 Sn2+-based perovskites show promising optoelectronic properties, but quick conversion of Sn2+ to Sn4+ is a big problem.26,27 Therefore, finetuning of the substituent concentration is required to stabilize the α-CsPbI3 at room temperature while retaining the inherent optoelectronic properties of α-CsPbI3. Within these constraints, there are some reports regarding improving the stability of αCsPbI3 by B-site doping or alloying, and Table 1 summarizes the results. The stability of α-CsPbI3 has evolved from a few hours to 5 months by different strategies and substituent ions. Clearly, various parameters including synthesis and washing methodologies also influence the stability of α-CsPbI3. Despite differences in various methodologies, crystallite size, and also X− ions, Table 1 suggests a significant role of partial B-site substitution in improving the stability of the α-CsPbI3 perovskite phase. One major structural aspect is that partial substitution at the B-site influences the Goldschmidt’s tolerance factor, R τ = 2 AR−X , where RA−X is the bond length between the AB−X

site cation and X-site anion and RB−X is the bond length between the B-site cation and X-site anion (Figure 2a).28 Along with X− anions, B-site cations determine the size of the [BX6]4− octahedra and hence determine the cubooctahedral voids for the A-site cation (Figure 2b,c). If the void size matches well Received: November 30, 2017 Accepted: December 7, 2017

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DOI: 10.1021/acsenergylett.7b01197 ACS Energy Lett. 2018, 3, 286−289

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Cite This: ACS Energy Lett. 2018, 3, 286−289

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ACS Energy Letters Table 1. Evolution of the Phase Stability of the α-CsPbI3 Perovskite at Room Temperature but Prepared by Following Different Strategies sample (ref) CsPbI35 CsPb0.96Bi0.04I315 CsPb0.98Sr0.02I2Br16 CsPb0.9Sn0.1IBr217 CsPbI36 CsPb0.88Mn0.12I319 CsPbI36 CsSn0.6Pb0.4I318a

phase stability

condition

Bulk unstable polycrystalline film in ambient >6 days polycrystalline film in ambient >30 days encapsulated polycrystalline film in device >100 days encapsulated polycrystalline film in device Nanocrystals 2 days unwashed colloidal dispersion in ambient >30 days unwashed colloidal dispersion in glovebox >60 days washed colloidal dispersion/film kept in dry air >150 days washed colloidal dispersion in ambient

a

In CsSn0.6Pb0.4I3NCs, Sn2+ has more contribution at the B-site. Hence, the crystal phase will be mainly decided by CsSnI 3 composition.

with the size (and shape) of the A-site cation, the B−X−B bond angle (θ) would be 180° (Figure 2a). This scenario leads to the ideal cubic perovskite phase with τ = 1. Typically, the problem is that the size of the A-site cation is smaller than the void size, leading to τ < 1. In such a situation, instead of decreasing RA−X, the [BX6]4− octahedra rotate and tilt to decrease the extra space around the A-site cation, resulting in θ < 180° (Figure 2b).28 For example, in CsPbI3, the reported tolerance factor is 0.807, and owing to that, it undergoes more octahedral rotation distortion in comparison to CsPbBr3 with a higher value of τ = 0.824.29,30 This larger extent of distortion transforms the blackcolored 3-D perovskite form of α-CsPbI3 into a nonperovskite (where [BX6]4− octahedra are not corner-shared) yellowcolored δ-phase and follows the orthorhombic crystallographic structure. It is to be noted that, before transforming into a nonperovskite (δ-) phase at room temperature, the hightemperature (360 °C) corner-shared α-phase of CsPbI3 undergoes transformations toward lower symmetrical structures because of the smaller octahedral tilting at intermediate temperatures forming two more black perovskite phases where the [BX6]4− octahedra are still corner-shared, namely, β-phase (at 260 °C) and γ-phase (at 175 °C).29 All three perovskite phases, α-, β-, and γ-CsPbI3, are unstable at room temperature, hindering their real-life application. Interestingly, CsPbBr3 with smaller RB−X leads to a higher value of τ and therefore maintains the three-dimensional corner-shared perovskite network at room temperature, even after a small octahedral distortion from cubic (∼130 °C) to orthorhombic crystal structure. All of the perovskite structures with cornershared [BX6]4− octahedra largely maintain their optoelectronic properties even after the octahedral tilting. However, when the corner sharing network breaks down, the optoelectronic properties suffer significantly. Now, instead of changing halide ions, smaller RB−X can also be achieved by partial substitution of Pb2+ ions by smaller B-site cations. Therefore, partial substitution of Pb2+ with a smaller B-site cation can stabilize the α-CsPbI3 by reducing the extent of octahedral rotation or tilt, as schematically shown in Figure 2b. Mathematically, as τ depends on the ratio of RA−X and RB−X, the decrease in RA−X

Figure 2. Schematic representations. (a) Relation of the tolerance factor (τ) with a B−X−B bond angle (θ) of the ABX3 perovskite structure. (b) Rotational distortion of [BX6]4− ([PbX6]4−) octahedra can be restricted by reducing the B−X bond length when Pb2+ is partially substituted with smaller B-site cations. Smaller B-site cations reduce the size of the [BX6]4− octahedron, which in turn decreases the size of the cuboctahedral void for the A-site cation. (c) The B-site cation is located at the corner position of a perovskite unit cell and also at the center of the [BX6]4− octahedron (left panel), and the [BX6]4− octahedron is shared by eight cuboctahedra (right panel). Therefore, a change in size of one B-site cation can influence the size of eight cuboctahedral voids by reducing the size of the centrally placed [BX6]4− octahedron.

due to using Cs+ instead of MA+ can be compensated by reduction of RB−X, through doping with smaller B-site cations. Furthermore, it is interesting to note that B-site cations are located at the corners and X-site anions are located at edges of the perovskite unit cell (as shown in Figure 2c). Consequently, each of the B-site cations is connected to eight cuboctahedra through [BX6]4− octahedra, whereas each of the X-site anions is shared by only four cuboctahedra. As mentioned above, the size of B-site cations can decide the size of the [BX6]4− octahedra and hence determines the size of cubooctahedral voids. Therefore, ignoring any possible structural relaxation, reduction in the size of one B-site cation can reduce the size of eight cuboctahedra and their voids. For example, just 12.5 mol % Mn-doping has the potential to reduce all (100%) of the cubooctahedral voids for Cs+ ions in the CsPbX3 lattice, whereas substitution with a smaller anion at the X-site can influence only four such cuboctahedral voids. Other structural factors, such as the octahedral parameter (RB/RX), also need to be considered while selecting the B-site cation.31 287

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ACS Energy Letters Unlike the orthorhombic nonperovskite δ-phase of CsPbI3, the orthorhombic phase of CsPbBr3 is a stable perovskite phase at room temperature and exhibits interesting optolectronic properties.32 It has been found that orthorhombic CsPbBr3 NCs exhibit nearly ideal photoluminescence (PL) efficiency and a low threshold for lasing.33 However, the PL efficiency degrades irreversibly upon the heating−cooling cycle in ambient conditions.21 Consequently, there is a need to improve the formation energy of the orthorhombic phase of CsPbBr3 NCs. Zou et al.21 reported partial substitution of Pb2+ with smaller sized Mn2+ ions to stabilize the efficiency of excitonic emission of CsPbBr3 throughout the heating−cooling cycle until 200 °C. This thermal stability of excitonic PL also led to the improved performance of light-emitting diodes after partially replacing Pb2+with Mn2+ in CsPbBr3 NCs. To corroborate these experimental observations, they did firstprinciples calculations, showing that substituent divalent metal ions such as Mn2+, Sr2+, Sn2+, Co2+, Zn2+, and Cd2+ in CsPbBr3 perovskite increase the thermodynamic stability of the orthorhombic structure. Figure 3 shows the increase in the

and conduction band minimum of CsPbX3 perovskites. Hence, replacing Pb2+ with other metal ions for phase stabilization may have the potential to bring new deep defect states, destroying the defect tolerance nature of the host CsPbX3.37 These new defect states may act as traps and scattering centers, hampering the optoelectronic performance. Therefore, B-site cations play the most important role in determining the optoelectronic properties of CsPbX3. Consequently, extreme care is needed in selecting the B-site dopants and their concentrations, such that interesting optoelectronic properties of host lead-halide perovskites are retained after doping or alloying. Though partial substitution of Pb2+ with Bi3+ and Sr2+ in a CsPbI3 host and with eight different divalent metal ions (Co2+, Cu2+, Mg2+, Mn2+, Ni2+, Sn2+, Sr2+, and Zn2+) in a MAPbI3 host has improved and/or maintained the solar cell performance owing to better phase stability and band energy alignment,15,16,38 the influence of dopants on charge transport properties needs to be studied further. Finally, stabilizing CsPbX3 by B-site doping offers a new approach to achieve stable optoelectronic devices, but the effect of various B-site dopants on the crystal structure and electronic structure of CsPbX3 needs to be understood in greater detail.

Abhishek Swarnkar*,† Wasim J. Mir*,† Angshuman Nag*,‡,† †

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Department of Chemistry, and ‡Centre for Energy Science, Indian Institute of Science Education and Research (IISER), Pune 411008, India

AUTHOR INFORMATION

Corresponding Authors

*E-mails: [email protected] (A.S.). *E-mail: [email protected] (W.J.M.). *E-mail: [email protected] (A.N.). ORCID

Wasim J. Mir: 0000-0002-0993-7452 Angshuman Nag: 0000-0003-2308-334X

Figure 3. Histograms comparing the first-principles calculation results for the change in formation energy (ΔEform) per divalent Pb2+ ion in undoped and upon doping with 2.08 mol % various metal ions in a CsPbBr3 nanocrystal. Reproduced from ref 21. Copyright 2017 American Chemical Society.

Notes

Views expressed in this Viewpoint are those of the authors and not necessarily the views of the ACS. The authors declare no competing financial interest.

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calculated change in formation energy (ΔEform) of orthorhombic CsPbBr3 NCs by substituting ∼2 mol % of B-site cation.21 Also, it is to be noted that doping the Mn2+ ion in the case of CsPbCl3 NCs gives rise to Mn2+ dopant emission and that doping Bi3+ in CsPbBr3 NCs influences interfacial charge transfer.34−36 In conclusion, it will be safe to state that the reduction in RB−X by partial substitution of the B-site (Pb2+) cation can increase the stability of the all-inorganic CsPbX3 perovskite, thereby improving the stability of their solar cells, luminescence, and other properties. However, understanding at the microscopic level of the structural reorganization by B-site doping is not yet available. Also, possible structural reorganizations by substituting the B-site cation as discussed above are not yet experimentally verified. Therefore, a detailed experimental and computational study is required to verify or fine-tune the above structure-related discussions. There are reports suggesting that the crystallite size of CsPbX3 can also influence the thermal stability.6 This observation again requires further understanding. Importantly, 6s and 6p orbitals of Pb2+ have significant contributions to the valence band maximum

ACKNOWLEDGMENTS A.S. and W.J.M. acknowledge IISER, Pune and CSIR, Govt. of India, respectively, for research fellowships. REFERENCES

(1) Pradhan, N.; Das Adhikari, S.; Nag, A.; Sarma, D. D. Luminescence, Plasmonic, and Magnetic Properties of Doped Semiconductor Nanocrystals. Angew. Chem., Int. Ed. 2017, 56, 7038−7054. (2) NREL Solar Cell Efficiency Chart. https://www.nrel.gov/pv/ assets/images/efficiency-chart.png (accessed November 30, 2017). (3) Juarez-Perez, E. J.; Hawash, Z.; Raga, S. R.; Ono, L. K.; Qi, Y. Thermal Degradation of CH3NH3PbI3 Perovskite into NH3 and CH3I Gases Observed by Coupled Thermogravimetry-Mass Spectrometry Analysis. Energy Environ. Sci. 2016, 9, 3406−3410. (4) Kulbak, M.; Gupta, S.; Kedem, N.; Levine, I.; Bendikov, T.; Hodes, G.; Cahen, D. Cesium Enhances Long-Term Stability of Lead Bromide Perovskite-Based Solar Cells. J. Phys. Chem. Lett. 2016, 7, 167−172. (5) Eperon, G. E.; Paterno, G. M.; Sutton, R. J.; Zampetti, A.; Haghighirad, A. A.; Cacialli, F.; Snaith, H. J. Inorganic Caesium Lead 288

DOI: 10.1021/acsenergylett.7b01197 ACS Energy Lett. 2018, 3, 286−289

Viewpoint

ACS Energy Letters Iodide Perovskite Solar Cells. J. Mater. Chem. A 2015, 3, 19688− 19695. (6) Swarnkar, A.; Marshall, A. R.; Sanehira, E. M.; Chernomordik, B. D.; Moore, D. T.; Christians, J. A.; Chakrabarti, T.; Luther, J. M. Quantum Dot−Induced Phase Stabilization of α-CsPbI3 Perovskite for High-Efficiency Photovoltaics. Science 2016, 354, 92−95. (7) Zhang, Y.; Grancini, G.; Feng, Y.; Asiri, A. M.; Nazeeruddin, M. K. Optimization of Stable Quasi-Cubic FAxMA1−xPbI3 Perovskite Structure for Solar Cells with Efficiency Beyond 20%. ACS Energy Lett. 2017, 2, 802−806. (8) Ghosh, D.; Walsh Atkins, P.; Islam, M. S.; Walker, A. B.; Eames, C. Good Vibrations: Locking of Octahedral Tilting in Mixed-Cation Iodide Perovskites for Solar Cells. ACS Energy Lett. 2017, 2, 2424− 2429. (9) Li, Z.; Yang, M.; Park, J.-S.; Wei, S.-H.; Berry, J. J.; Zhu, K. Stabilizing Perovskite Structures by Tuning Tolerance Factor: Formation of Formamidinium and Cesium Lead Iodide Solid-State Alloys. Chem. Mater. 2016, 28, 284−292. (10) Sharma, S.; Weiden, N.; Weiss, A. Phase Diagrams of Quasibinary Systems of the Type: ABX3  A′BX3; ABX3  AB′X3, and ABX3  ABX′3; X = Halogen. Z. Phys. Chem. 1992, 175, 63−80. (11) Hoffman, J. B.; Schleper, A. L.; Kamat, P. V. Transformation of Sintered CsPbBr3 Nanocrystals to Cubic CsPbI3 and Gradient CsPbBrxI3−x through Halide Exchange. J. Am. Chem. Soc. 2016, 138, 8603−8611. (12) 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. (13) Sim, K. M.; Swarnkar, A.; Nag, A.; Chung, D. S. Phase Stabilized α-CsPbI3 Perovskite Nanocrystals for Photodiode Applications. Laser Photonics Rev. 2017, 1700209. (14) Sanehira, E. M.; Marshall, A. R.; Christians, J. A.; Harvey, S. P.; Ciesielski, P. N.; Wheeler, L. M.; Schulz, P.; Lin, L. Y.; Beard, M. C.; Luther, J. M. Enhanced mobility CsPbI3 quantum dot arrays for record-efficiency, high-voltage photovoltaic cells. Sci. Adv. 2017, 3, 10. (15) Hu, Y.; Bai, F.; Liu, X.; Ji, Q.; Miao, X.; Qiu, T.; Zhang, S. Bismuth Incorporation Stabilized α-CsPbI3 for Fully Inorganic Perovskite Solar Cells. ACS Energy Lett. 2017, 2, 2219−2227. (16) Lau, C. F. J.; Zhang, M.; Deng, X.; Zheng, J.; Bing, J.; Ma, Q.; Kim, J.; Hu, L.; Green, M. A.; Huang, S.; Ho-Baillie, A. StrontiumDoped Low-Temperature-Processed CsPbI2Br Perovskite Solar Cells. ACS Energy Lett. 2017, 2, 2319−2325. (17) Liang, J.; Zhao, P.; Wang, C.; Wang, Y.; Hu, Y.; Zhu, G.; Ma, L.; Liu, J.; Jin, Z. CsPb0.9Sn0.1IBr2 Based All-Inorganic Perovskite Solar Cells with Exceptional Efficiency and Stability. J. Am. Chem. Soc. 2017, 139, 14009−14012. (18) Liu, F.; Ding, C.; Zhang, Y.; Ripolles, T. S.; Kamisaka, T.; Toyoda, T.; Hayase, S.; Minemoto, T.; Yoshino, K.; Dai, S.; et al. Colloidal Synthesis of Air-Stable Alloyed CsSn1−xPbxI3 Perovskite Nanocrystals for Use in Solar Cells. J. Am. Chem. Soc. 2017, 139, 16708−16719. (19) Akkerman, Q. A.; Meggiolaro, D.; Dang, Z.; De Angelis, F.; Manna, L. Fluorescent Alloy CsPbxMn1−xI3 Perovskite Nanocrystals with High Structural and Optical Stability. ACS Energy Lett. 2017, 2, 2183−2186. (20) Van Der Stam, W.; Geuchies, J. J.; Altantzis, T.; van den Bos, K. H. W.; Meeldijk, J. D.; Van Aert, S.; Bals, S.; Vanmaekelbergh, D.; de Mello Donega, C. Highly Emissive Divalent-Ion-Doped Colloidal CsPb1−xMxBr3 Perovskite Nanocrystals through Cation Exchange. J. Am. Chem. Soc. 2017, 139, 4087−4097. (21) Zou, S.; Liu, Y.; Li, J.; Liu, C.; Feng, R.; Jiang, F.; Li, Y.; Song, J.; Zeng, H.; Hong, M.; Chen, X. Stabilizing Cesium Lead Halide Perovskite Lattice through Mn(II) Substitution for Air-Stable LightEmitting Diodes. J. Am. Chem. Soc. 2017, 139, 11443−11450. (22) Eames, C.; Frost, J. M.; Barnes, P. R. F.; O’Regan, B. C.; Walsh, A.; Islam, M. S. Ionic Transport in Hybrid Lead Iodide Perovskite Solar Cells. Nat. Commun. 2015, 6, 7497.

(23) Park, B. W.; Philippe, B.; Zhang, X.; Rensmo, H.; Boschloo, G.; Johansson, E. M. J. Bismuth Based Hybrid Perovskites A3Bi2I9 (A: Methylammonium or Cesium) for Solar Cell Application. Adv. Mater. 2015, 27, 6806−6813. (24) Pal, J.; Manna, S.; Mondal, A.; Das, S.; Adarsh, K. V.; Nag, A. Colloidal Synthesis and Photophysics of M3Sb2I9 (M = Cs and Rb) Nanocrystals: Lead-Free Perovskites. Angew. Chem., Int. Ed. 2017, 56, 14187−14191. (25) Mir, W. J.; Warankar, A.; Acharya, A.; Das, S.; Mandal, P.; Nag, A. Colloidal Thallium Halide Nanocrystals with Reasonable Luminescence, Carrier Mobility and Diffusion Length. Chem. Sci. 2017, 8, 4602−4611. (26) Swarnkar, A.; Ravi, V. K.; Nag, A. Beyond Colloidal Cesium Lead Halide Perovskite Nanocrystals: Analogous Metal Halides and Doping. ACS Energy Lett. 2017, 2, 1089−1098. (27) Chung, I.; Song, J.-H.; Im, J.; Androulakis, J.; Malliakas, C. D.; Li, H.; Freeman, A. J.; Kenney, J. T.; Kanatzidis, M. G. CsSnI3: Semiconductor or Metal? High Electrical Conductivity and Strong Near-Infrared Photoluminescence from a Single Material. High Hole Mobility and Phase-Transitions. J. Am. Chem. Soc. 2012, 134, 8579− 8587. (28) Hwang, H. Y.; Cheong, S. W.; Radaelli, P. G.; Marezio, M.; Batlogg, B. Lattice Effects on the Magnetoresistance in Doped LaMnO3. Phys. Rev. Lett. 1995, 75, 914−917. (29) Stoumpos, C. C.; Kanatzidis, M. G. The Renaissance of Halide Perovskites and Their Evolution as Emerging Semiconductors. Acc. Chem. Res. 2015, 48, 2791−2802. (30) Brennan, M. C.; Herr, J. E.; Nguyen-Beck, T. S.; Zinna, J.; Draguta, S.; Rouvimov, S.; Parkhill, J.; Kuno, M. Origin of the SizeDependent Stokes Shift in CsPbBr3 Perovskite Nanocrystals. J. Am. Chem. Soc. 2017, 139, 12201−12208. (31) Li, C.; Lu, X.; Ding, W.; Feng, L.; Gao, Y.; Guo, Z. Formability of ABX3 (X = F, Cl, Br, I) halide perovskites. Acta Crystallogr., Sect. B: Struct. Sci. 2008, 64, 702−707. (32) Swarnkar, A.; Chulliyil, R.; Ravi, V. K.; Irfanullah, M.; Chowdhury, A.; Nag, A. Colloidal CsPbBr3 Perovskite Nanocrystals: Luminescence beyond Traditional Quantum Dots. Angew. Chem., Int. Ed. 2015, 54, 15424−15428. (33) Sutherland, B. R.; Sargent, E. H. Perovskite photonic sources. Nat. Photonics 2016, 10, 295. (34) 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. (35) Mir, W. J.; Jagadeeswararao, M.; Das, S.; Nag, A. Colloidal MnDoped Cesium Lead Halide Perovskite Nanoplatelets. ACS Energy Lett. 2017, 2, 537−543. (36) Begum, R.; Parida, M. R.; Abdelhady, A. L.; Murali, B.; Alyami, N. M.; Ahmed, G. H.; Hedhili, M. N.; Bakr, O. M.; Mohammed, O. F. Engineering Interfacial Charge Transfer in CsPbBr3 Perovskite Nanocrystals by Heterovalent Doping. J. Am. Chem. Soc. 2017, 139, 731−737. (37) Maughan, A. E.; Ganose, A. M.; Bordelon, M. M.; Miller, E. M.; Scanlon, D. O.; Neilson, J. R. Defect Tolerance to Intolerance in the Vacancy-Ordered Double Perovskite Semiconductors Cs2SnI6 and Cs2TeI6. J. Am. Chem. Soc. 2016, 138, 8453−8464. (38) Klug, M. T.; Osherov, A.; Haghighirad, A. A.; Stranks, S. D.; Brown, P. R.; Bai, S.; Wang, J. T. W.; Dang, X.; Bulovic, V.; Snaith, H. J.; Belcher, A. M. Tailoring metal halide perovskites through metal substitution: influence on photovoltaic and material properties. Energy Environ. Sci. 2017, 10, 236−246.

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