Beyond Colloidal Cesium Lead Halide Perovskite Nanocrystals

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Beyond Colloidal Cesium Lead Halide Perovskite Nanocrystals: Analogous Metal Halides and Doping Abhishek Swarnkar, Vikash Kumar Ravi, and Angshuman Nag ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.7b00191 • Publication Date (Web): 07 Apr 2017 Downloaded from http://pubs.acs.org on April 7, 2017

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Beyond Colloidal Cesium Lead Halide Perovskite Nanocrystals: Analogous Metal Halides and Doping Abhishek Swarnkar,†,* Vikash Kumar Ravi,† Angshuman Nag‡,†,* †

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

*Corresponding authors’ e-mails: AN: [email protected] AS: [email protected] Abstract: Colloidal CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) are being explored extensively as an interesting variety of defect-tolerant materials, wherein high efficiencies of optical and optoelectronic processes can be achieved even in the presence of surface defects. This defecttolerant nature arises mainly because of the unique electronic band structure of these perovskites. Consequently, synthesis and exploring other metal halide {CsSnX3, Cs2SnX6, and (CH3)3Bi2X9} NCs with electronic band structure similar to CsPbX3 perovskite have begun with high promises. Another initiative to tailor properties is by doping metal ions (Mn2+ and Bi3+) into the lattice of CsPbX3 NCs. Furthermore, nanocomposites of CsPbX3-metal and CsPbX3-dielectric layer-metal have been attempted. Here we discuss the recent progress in the research of these colloidal metal halide NCs that are either analogous to CsPbX3 perovskites, or derivative of CsPbX3 perovskites.

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Colloidal semiconductor nanocrystals (NCs) became popular in last three decades because of both fundamental properties and applications including energy related ones, like solar cells, light emitting diodes (LEDs), and photocatalysis.1,2 One of the major problems of these NCs is the large density of surface defects that traps charge carriers and consequently decrease the efficiency of electronic, optical and optoelectronic processes.3 These surface defects are integral part of a NC and cannot be removed. Therefore, making a defect-free (or low defect density) NC is probably not an option. Instead, researchers mainly focus on manipulating energy levels of such defect states, in an attempt to achieve defect-tolerant system. Typically, electrons in the conduction band minimum (CBM) and holes in the valence band maximum (VBM) are responsible for optoelectronic processes in a semiconductor. Therefore, if energy levels of defect states can be removed from the bandgap region, then the defects are less likely to trap the charge carriers. For example, in a type-I core/shell NCs like CdSe/ZnS, the shell helps to remove the defect states from the bandgap of CdSe core, achieving nearly ideal photoluminescence (PL) quantum yield (QY) from the core.4,5 But such a shell inhibits injection or extraction of charge carriers from the core, hindering the electronic and optoelectronic applications. Manipulation of


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energy levels of surface states by using various organic and inorganic molecular species has also been demonstrated.3 In last couple of years, colloidal cesium lead halide perovskite, CsPbX3 (X = Cl, Br, I) NCs have been explored as a new kind of defect-tolerant system.6-9 Unlike previous strategies of manipulating surface related defect states, intrinsic electronic band structure of CsPbX3 mainly imparts the defect-tolerance nature.10 Interesting properties including nearly ideal PL QY,6 suppression of PL blinking,7 low-threshold for lasing,11 efficient LEDs12,13 and solar cells,14 have already been demonstrated. Recently, several review articles15-24 have been published summarizing the exciting prospects of colloidal CsPbX3 and organic-inorganic lead halide perovskite NCs. Therefore, we have not repeated such discussion in this perspective. Instead, we discuss here the progress of less explored colloidal metal halide NCs which are either analogous or derivative of CsPbX3 (X = Cl, Br, I) NCs. The perspective has been divided into sub-sections namely, (i) origin of defect-tolerance in CsPbX3 NCs and analogous systems, (ii) Pb-free (defecttolerant?) metal halide NCs, (iii) metal ion doping in CsPbX3 NCs, (iv) CsPbX3-metal nanocomposites and (v) electronic, optical and optoelectronic applications Origin of Defect-Tolerance in CsPbX3 NCs and Analogous Systems. The defect tolerant nature of bulk CsPbX3 or CH3NH3PbX3 (X= Cl, Br, I) is mainly because of their electronic band structure wherein VBM is anti-bonding in nature, and CBM gets stabilized by strong spin-orbit coupling,10,25 as opposed to common II-VI and III-V semiconductors wherein VBM is constituted by bonding orbitals. Early study done on lead iodide NCs showed some interesting results.26 Schematic representation of valence band structure of CsPbX3 with respect to isolated valence p and s atomic orbitals of Pb and X are shown in Figure 1a.


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Figure 1: a) Schematic representation of bonding (σ) and anti-bonding (σ*) orbitals of CsPbX3 showing the formation of the valence and conduction band. b) Schematic representation showing CsPbBr3 NCs maintains PL brightness even when defect is introduced in form of removal of surface atoms and ligands. c) Carrier mobility within the colloidal CsPbBr3 NCs obtained by using ultrafast THz spectroscopy. The mobility has been plotted as a function of delay between the optical pump and THz probe. The red dash line shows the average mobility after pump-probe delay of 20 ps. Inset shows photograph of highly luminescent CsPbX3 NCs- polymer (PMMA) monoliths under UV irradiation (λexc. =365 nm). Figure 1a is adapted from ref 27. Figure 1b is adapted from ref 9. Figure 1c is reprinted from ref 8. Inset of Figure 1c is adapted from ref 6.

Taking CsPbI3 as a representative member of CsPbX3 family, VBM originates from the Pb(6s)– I(5p) anti-bonding interactions and CBM originates from the Pb(6p)–I(5p) anti-bonding interactions, but the CBM is less hybridized and is mainly dominated by Pb 6p contribution. Interestingly, the CBM gets further stabilized by spin-orbit splitting of Pb 6p states. The Cs+ which is acting as A-site cation in ABX3 perovskite structure of CsPbI3 do not contribute directly to VBM and CBM. But indirectly, the size of A-site cation can expand or contract the perovskite lattice causing a change in band gap.28,29 Dangling bonds on the surface of a NC are typically non-bonding in nature, and arise in between bonding and anti-bonding states. But since bonding orbitals are not involved in both VBM and CBM, and CBM gets stabilized by spin-orbit coupling, it is less likely that such defect related dangling bonds will form a deep state in the


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bandgap. If the defect states lie within valence/conduction band, or forms a shallow state near to VBM and CBM, then such a defect state will be nearly delocalized in nature, and will not form an efficient localized trap state. In fact, first-principles calculations verifies this fact by showing that point defects in CsPbBr3 forms only shallow states, maintaining its good electronic quality, in spite of having defects.30 It is to be noted that similar possibilities of defect-tolerance with shallow states have also been discussed in some other visible-light active semiconductors, such as I-III-VI compound semiconductor and Cu3N.31-33 The above discussion involves only the states originating from inorganic part, which is the case for a bulk crystal. However, organic capping ligands are also an integral part of colloidal NCs, which can contribute to new trap states within the bandgap. With recent experimental studies, it is becoming evident that the major capping ligand on highly luminescent CsPbBr3 nanocubes are oleylammonium ions.34 Brinck et al9 used a similar model by employing methylammonium ion as capping ligand instead of oleylammonium and calculated the electronic structure of methylammonium capped CsPbX3 NCs. Their results show that such capping ligands do not contribute to localized trap states within the bandgap. Furthermore, creation of dangling bonds by removing some of the surface atoms and/or capping molecules does not introduce trap sates, which has been schematically shown in Figure 1b, indicating removal of surface atoms/molecules does not decrease brightness of PL.9 This expectation of defect-tolerant behavior in colloidal CsPbBr3 NCs got successfully translated to experimental results in terms of various optical and optoelectronic properties. For example, Protesescu et al6 showed nearly ideal PL efficiency from colloidal CsPbBr3 NCs. Inset to Figure 1c represents such intense luminescence from CsPbX3 NCs-PMMA polymer monoliths, where different colors across the visible region was achieved by changing the halide compositions. 5 ACS Paragon Plus Environment

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Yettapu et al8 used terahertz (THz) spectroscopy establishing long-lived carriers in ~11 nm CsPbBr3 NCs yielding high carrier mobility of ~ 4500 cm2V-1s-1, and large diffusion length of > 9.2 µm (Figure 1c). This successful demonstration of defect-tolerant behavior of CsPbBr3 NCs have motivated researchers to explore newer colloidal metal halide NCs, that exhibit electronic band structure similar to that of CsPbBr3. To start the screening for an alternative semiconductor NC, one may look for both (i) anti-bonding VBM, which often arises from metal ions with ns2 electronic configuration in the outer most s orbital, and (ii) stabilization of CBM by spin-orbit coupling. Furthermore, lower effective mass of charge carriers will be helpful for better carrier mobility. Pb-Free (Defect-Tolerant?) Metal Halide NCs. Toxicity is a concern for real-life applications of Pb containing perovskites. Colloidal metal halide NCs containing tin (Sn), germanium (Ge), Indium (In) bismuth (Bi) and antimony (Sb) can be explored as a replacement for Pb halides. For the sake of curiosity and better understanding, toxic thallium halides (TlX) also can be explored. The resemblance among Sn2+, Bi3+, Sb3+, In+, Tl+ and Pb2+ is the ns2 electronic configuration in the outer most s orbital. Such electronic configuration can provide anti-bonding VBM, as discussed in the earlier sub-section. Sn is just above the Pb in the group-IV of periodic table. Therefore, it is desired to replace Pb2+ with non-toxic Sn2+, forming colloidal CsSnX3 perovskite NCs. Jellicoe et al35 have synthesized colloidal CsSnX3 (X= Cl, Cl0.5Br0.5, Br, Br0.5I0.5, I) perovskite NCs (Figure 2 a-c), by extending the protocol for synthesizing CsPbX3 NCs developed by Protesescu et al.6 Optical absorption and PL spectra of colloidal CsSnX3 NCs in Figure 2b shows the tuning of optical bandgaps from the visible to the near-infrared (NIR) region of the electromagnetic spectrum. Such spectral tunability was achieved by controlling both halide composition and size of CsSnX3 NCs.35 6 ACS Paragon Plus Environment

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Interestingly, CsSnI3 NCs with optical bandgap ~950 nm (1.3 eV)35 absorbing from visible to NIR could be a better light harvester when compared to CsPbI3 NCs14,36 which absorb only the visible part of the sunlight. This shift of optical bandgap of CsSnI3 NCs towards longer wavelength is because of the higher electronegativity value of Sn2+ compared to Pb2+. Indeed there were attempts to extend the light absorption from visible to NIR region by alloying bulk

CH3NH3PbI3 perovskite with Sn2+.37 One of the interesting material design aspects of colloidal CsPbX3 NCs is post-synthesis anion exchange reaction, where the halide composition of the already synthesized NCs can be reversibly varied from Cl to Br to I including intermediate mixed halide compositions.38-40 Similar post-synthesis anion exchange reaction was also achieved for CsSnX3 NCs.35 Such anion exchange processes can yield the desired composition, and hence, desired bandgap maintaining the size and shape of the NC.

Figure 2: Colloidal Pb-free metal halide NCs analogous to CsPbX3 perovskites.

a) Schematic

representation of cubic phase CsSnX3 perovskite structure (left panel) with cuboidal morphology (right panel). Note: Experimentally, CsSnCl3 NCs follow tetragonal crystallographic phase while CsSnBr3 and 7 ACS Paragon Plus Environment

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CsSnI3 NCs exhibit orthorhombic phase. b) UV-visible-NIR absorption and PL spectra of CsSnX3 NCs. c) TEM image of CsSnI3 NCs. d) Schematic showing crystal structure of the vacancy-ordered double perovskites of Cs2SnI6. e) Schematic of procedures for the synthesis of colloidal Cs2SnI6 NCs with different morphologies, along with photographs of Cs2SnI6 NCs under UV-light. f) HRTEM image of a spherical (CH3NH3)3Bi2Br9 NC. Right inset and left inset show the corresponding FFT image and the photograph of luminescent colloidal (CH3NH3)3Bi2Br9 NCs under UV-light respectively. g) Tuning of UV-visible absorption and PL spectra of (CH3NH3)3Bi2Br9 NCs by halide substitution. h) Left panel is the structure of adopted quaternary Cs2M+M3+X6 double perovskite and the right panel shows the schematic of possible cation transmutation to get stable lead-free perovskite. Figures 2b-c are adapted from ref 35. Figure 2d is reprinted from ref

41

. Figure 2e is reprinted from ref

42

. Figure 2h is adapted from ref 43.

Figure 2f-g are adapted from ref 44, copyright permission obtained from Wiley Online Library.

An important parameter deciding the quality of colloidal semiconductor NC is PL QY. The PL QY of CsSnX3 NCs is extremely low (0.14%).35 This lower PL QY of CsSnX3 suggests significant contribution of trap states, in contrast to the expectation of defect-tolerant nature. Such trap states might arise from undesirable and uncontrolled conversion of Sn2+ to Sn4+, as the oxidation potential of Sn2+/Sn4+ (-0.15 V)45 suggesting Sn4+ is the more stable state compared to Sn2+ in oxidizing atmosphere (ambient condition). Whereas, oxidation potential of Pb2+/ Pb4+ is 1.8 V45 which is more negative than that of Sn2+/Sn4+, making Pb2+ a stable state in CsPbX3 NCs. Poor stability of Sn2+ based halide perovskites has also been observed in the bulk samples.46,47 Furthermore, for NCs the problem of oxidation become more severe because of the larger surface to volume ratio. Another relevant comparison is the weaker stabilization of CBM of CsSnX3 compared to CsPbX3, because of lower spin-orbit coupling of Sn2+ 5p state compared to that of Pb2+ 6p state.48,49 This lowering of spin-orbit coupling increases the probability of trap states in CsSnX3 NCs. To the best of our knowledge, synthesis of stable CsSnX3 NCs with reasonable PL QY still remains a challenge. An improvement in reaction condition along with suitable washing of the NCs can stop the oxidation of Sn2+ to Sn4+. NCs with strongly bound 8 ACS Paragon Plus Environment

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ligands and using excess of SnX2 in reaction medium with reducing surface chemistry can possibly help to improve the long term stability of Sn2+ based halide perovskite NCs.50,51 Maughan et al41 reported that the bulk Cs2SnI6 can be a defect-tolerant system with Sn in more stable Sn4+ state. Cs2SnI6 exhibits a modified perovskite structure. Figure 2d shows vacancy ordered double perovskite structure of Cs2SnI6, by replacing two Sn2+ sites in CsSnI3 perovskites structure with one Sn4+ and one vacancy site, where the halides do not share the isolated octahedrons. Cs+ cation occupies cuboctahedra voids. Density functional theory (DFT) calculations shows iodine vacancies exhibit a low enthalpy of formation, introducing shallow donor levels to the conduction band, rendering defect tolerant nature to Cs2SnI6.41 Indeed, experimental results show higher four-probe electrical conductivity from the pellet of bulk Cs2SnI6. Wang et al42 reported the synthesis of colloidal Cs2SnI6 NCs with various shapes, as schematically shown in Figure 2e. But, here again the PL QY is poor (10 nm) of nanocubes is larger than the Bohr excitonic diameter of the host and consequently exhibits a weak quantum confinement of charge carriers. Stronger quantum confinement of charge carriers in Mn-doped CdSe NCs enhances coupling between exciton and dopant ion resulting into interesting magneto-optic properties.75 Mir et al83 reported Mn2+ doping in CsPbCl3 nanoplatelets (NPLs) with thickness 2.2 nm showing strong quantum confinement of charge carriers (Figure 3 f-g). Though Mn doping was successful in nanocubes and NPLs of CsPbCl3, it was found to be difficult in other halides counterparts like CsPbBr3 and CsPbI3.81 Consequently, an anion exchange process was employed converting Mn-doped CsPbCl3 NCs to other halide systems with partial success.81,83 The doping mechanism of Mn in different halide compositions of CsPbX3 NCs is not yet understood completely. Furthermore, magneto-optic properties of Mndoped CsPbX3 NCs are needed to be explored.


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Figure 3: Optical characterization of Mn- and Bi- doped CsPbX3 NCs. a) Schematic showing synthetic protocol for Mn-doped CsPbCl3 nanocubes. b) Comparison of PL spectra of Mn-doped and undoped CsPbCl3 nanocrystals. Inset shows the cartoon of cubic shaped yellow-orange luminescent Mn doped CsPbCl3 nanocubes. c) Photograph PL under UV-light, and d) UV-visible absorption spectra of colloidal Mn-doped CsPbCl3 nanocubes with varying Mn content. e) Schematics showing the tunability of luminescence color from CsPbxMn1−xCl3 NCs on varying both Mn-to-Pb precursor ratio and reaction temperature. f) Schematic showing the room temperature synthetic protocol of Mn doped NPLs in presence of oleic acid (OA), oleylamine (OLA) and 1-octadecene (ODE). g) Schematic representation showing PL originating for Mn-dopants, and corresponding PL spectrum of 0.8% Mn-doped CsPbCl3 nanoplatelets. h) UV-visible absorption, and i) PL spectra of Bi-doped CsPbBr3 NCs with various dopant concentrations. Figure 3a-b are reproduced from ref 80. Figure 3c -d are adapted from ref 81. Figure 3e is reproduced from ref 82. Figure 3f -g are adapted from ref 83. Figure 3h-i are adapted from ref 84.


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In the context of isovalent doping, apart from Mn doping, recently other divalent metals ions like Sn2+, Cd2+ and Zn2+ have also been doped in CsPbBr3 NCs by post-synthetic cation exchange reaction.85 In this doping process Pb2+ ions get exchanged up to 10 % with Sn2+/Cd2+/Zn2+ ions resulting into blue shift of the optical spectra without influencing high QY (~60%), and narrow spectra line-width (~80 meV) of PL. The blue-shift of optical spectra is due to the contraction of the perovskite unit cell which causes increased interaction between of Pb and Br orbitals.85 After isovalent substitution of Pb2+ with Mn2+, Sn2+, Cd2+ and Zn2+ Begum et al84 reported doping heterovalent Bi3+ into CsPbBr3 NCs. Figure 3h and 3i compare the UV-visible absorption and PL spectra of Bi-doped CsPbBr3 NCs with different Bi concentrations. At lower doping concentration (~ 0.25% Bi) a red shift in optical gap is observed because of fewer defect levels below the lowest energy excitonic state, however, at a higher level of doping (2.1% Bi) a bluesift is observed because of the evolution of defect state above the lowest energy excitonic state.84 Also, on increasing the content of Bi doping there is decreases in PL QY. All these results suggest that Bi3+ doping introduces charge carrier, which then modulates the rate of interfacial electron transfers between the NCs and molecular acceptors.84. Recently, Li+ has been intercalated electrochemically in bulk CsPbBr3 causing n type doping,86 a similar electrochemical doping in CsPbBr3 NCs is yet to be explored.

CsPbX3-Metal Nanocomposites. Metal-semiconductor heterostructure at nanoscale are interesting for photocatalysis and optoelectronic applications.87,88 In this regard, Balakrishnan et al89 have shown a selective growth of gold (Au) nanoparticles with diameter ~1.5 nm on the corners of ~ 7 nm CsPbBr3NCs as shown in Figure 4. This nano-scale heterostructure of CsPbBr3−Au has been prepared by reacting AuX3 (X = Cl, Br) on pre-synthesized CsPbBr3 NCs.


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Au3+ get reduced to Au0 by the dynamic ligands on surface of CsPbBr3 NCs. Since the Au metal is in direct contact with the semiconductor NC, PL QY due to CsPbBr3 component decreases in this CsPbBr3−Au heterostructure because of the charge-transfer between photoexcited CsPbX3 NCs and Au NCs. Such charge transfer in nano-scale metal-semiconductor heterostructure can enhance the performance of CsPbX3 NCs in photocatalysis and other light harvesting applications. However, a better stability of CsPbX3 toward polar solvents is required for many such photocatalytic applications.

Figure 4: Nano-scale CsPbBr3−Au heterostructure. High resolution scanning transmission electron microscopy (STEM) image along with schematic showing reduction of Au3+ on the corner of CsPbBr3 nanocubes of size ~ 7 nm. When AuBr3 precursor was reacted with CsPbBr3 NCs, then CsPbBr3−Au heterostructures were formed, but use of AuBr3 precursor yielded CsPb(BrxCl1-x)3−Au heterostructures. Figure 4 is reprinted from ref 89.

Plasmonics of Metal NCs can also interact with CsPbX3 NCs through a dielectric spacer. Coupling between plasmonic and excitonic transitions in metal-dielectric-CsPbX3 layers has been less explored.90


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Electronic, Optical and Optoelectronic Applications. In this subsection we will summarize sporadic attempts of different applications using films of colloidal metal halide NCs that are either analogous to CsPbX3 NCs or derivative of CsPbX3 NCs. Field Effect Transistors (FETs) using Cs2SnI6 nanobelts. FET data (Figure 5 a-b) show that holes are the major charge carriers in Cs2SnI6 nanobelts. Source-drain current decreases on increasing the voltage applied to gate showing p-type semiconductor behavior. Films of Cs2SnI6 was already explored as hole transporting material (HTM) in dye sensitized solar cells,91 which are in accordance with the FET results of Cs2SnI6 nanobelts. Interestingly, FET mobility of hole in Cs2SnI6 nanobelts was found to be 20.2 cm2V-1s-1 which is a reasonably high number for various optoelectronic applications. The concentration of hole in Cs2SnI6 nanobelts is 9.1×1018 cm−3.42 A performance stability of ~2 week was observed when the device was stored under ambient conditions. To the best our knowledge, FET properties of colloidal perovskite NCs has been less explored compared to their bulk counterpart.92,93 Doped CsPbX3 NCs as a color converting material. Liu et al82 prepared an LEDs based on solution processed colloidal Mn-doped CsPbCl3 NCs. Figure 5c shows a photograph of an orange-red glowing down-conversion LED made by coating a mixture of curable resin and Mndoped CsPbCl3 NCs on top of a UV (365 nm GaN based) LED. Inset shows the photograph of as prepared LED under normal light when the device is switched off. The orange-red LED continued to emit intense light with luminous efficiency 2.2 Lm/W (not very high in compared to other phosphor materials)94 for 200 hours when working at constant voltage of 3.5 V. These results suggest the doped perovskite NC can be used as color conversion material in display technology. Electroluminescent (EL) devices based on Mn-doped CsPbX3 NCs are needed to be explored.


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Figure 5: a) Schematic of a FET device, and b) the corresponding transfer characteristics (Ids vs Vgs at Vds = 10 mV) showing using a film of Cs2SnI6 nanobelts as a channel. Black line and red line correspond to positive and negative scan respectively. c) Photograph of orange-red luminescence obtained after coating an UV-LED (GaN LED) with a mixture of curable resin and solution processed Mn-doped CsPbCl3 NCs., under applied voltage of 3.5 V. Inset shows the optical image of the same LED. d) Schematic along with corresponding TEM image of plasmon enhanced LED device prepared by sandwiching N,N′-bis(1naphthalenyl)-N,N′-bis(phenylbenzidine) (NPB) dielectric layer in between layers of luminescent CsPbBr3 NC and plasmonic Ag nanorods . e) Comparison of electroluminescence (EL) spectra of plasmon enhanced LED shown in Figure 5d, with a control device without the Ag nanorod plasmonic layer. f) fluorescence-lifetime imaging microscopy (FLIM) image of CsPbBr3 thin films with (dimmer


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right side image) and without (brighter left side image) Ag rod. Figure 5 a-b are reprinted from ref 42. Figure 5c is reprinted from ref 82. Figure 5d-f are reprinted from ref 90.

Plasmon enhanced LED. Enhancement of luminescence through the interaction of CsPbBr3 NCs and Ag nanorod was observed by using N,N′-bis(1-naphthalenyl)-N,N′-bis(phenylbenzidine) (NPB) thin layer acting as dielectric spacer between layers of CsPbBr3 NC and Ag nanorods (Figure 5d).90 Surface plasmon resonance energy of Ag nanorod was matched with the emission energy of CsPbBr3 NCs to achieve efficient energy transfer in between plasmon of Ag-nanorod and excitons of CsPbX3 NCs, and therefore, enhancing the PL QY. Zhang et al90 fabricated the plasmonic LED as shown in Figure 5d. EL data in Figure 5e show plasmon enhanced LED of luminance value 8911 cd m-2 (42% higher luminance than non plasmonic CsPbBr3 LED) with current efficiency of 1.42 A-1 (43% higher current efficiency than non plasmonic CsPbBr3 LED) and external quantum efficiency (EQE) of 0.43% (43.3% higher EQE than non plasmonic CsPbBr3 LED which shows only 0.30% of EQE). Such plasmonic enhancement needs to be checked in a device with higher EQE. Fluorescence-lifetime imaging microscopy (FLIM) image of CsPbBr3 NCs exhibits a dimmer color when Ag nanorod is present which suggests the decrease in excited state life time of CsPbBr3 NCs due to exciton-plasmon coupling.

Conclusions and future challenges. Here we discussed the progress made in synthesis, optical properties, and applications (electronic, optical and optoelectronic) of colloidal metal halide NCs that are either analogous to CsPbX3 NCs, or derivative of CsPbX3 NCs. Efforts in this direction have just begun in last one year. Preliminary findings promise interesting properties of such metal halide NCs. For example, reasonably high (~10%) PL QY of TlX and (CH3NH3)3Bi2X9 NCs in the UV-blue region is noteworthy. But the material design and properties are not yet 18 ACS Paragon Plus Environment

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optimized. Synthesis of Pb-free NCs such as CsSnX3, Cs2SnI6, TlX, (CH3NH3)3Bi2X9 NCs are still inferior compared to that of CsPbX3 NCs in terms of stability and homogeneity in size-shape of NCs. Colloidal synthesis of other Pb-free halide NCs, based on Sb, Ge and Bi can be explored. There is no available report on Ge based perovskite NCs but based on their bulk counterpart, such synthesis is possible in near future.71 Subsequently, photophysics of these Pbfree halide NCs needs to be studied providing better understanding of the processes of generation, recombination and dissociation of excitons. In case of CsPbX3 NCs, size of NCs may increase during the fabrication of a device decreasing the optical bandgap.14 Similarly, contamination with other halides can change the bandgap of CsPbX3 NCs. In such circumstances, the chromaticity of Mn d-d emission from Mn-doped CsPbX3 NCs will remain unchanged at ~580 nm irrespective of variation in size and halide composition. Furthermore, Mn d-d emission is less susceptible to both self-absorption and resonance energy transfer because of the large Stokes’ shift between Mn emission and excitonic absorption.75 All these properties suggest that Mn-doped CsPbX3 NCs is an interesting candidate for stable and efficient LED applications. Not only for light emission application, long PL life time (~1.6 ms) of Mn-doped NCs can also be utilized to improve the efficiency of solar cells.78 Similarly, Bi doping can enhance the interfacial charge transfer rates.84 Such metal ion doped CsPbX3 NCs are needed to be explored for various energy-related applications like LEDs, photovoltaic, and photocatalysis. Also, the magneto-optic properties of Mn-doped CsPbX3 NCs are not yet explored. Interestingly, PL QY of Mn emission from Mn-doped CsPbCl3 NCs is many folds (sometime close to an order magnitude) larger than the PL QY excitonic emission in undoped CsPbCl3.80-83


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A similar strategy of doping can be also employed for lead-free halide NCs to improve the PL QY. Anchoring a small metal NC on the surface of CsPbX3 NCs, like Au-CsPbBr3 heterostructure,89 can be a first step to solder adjacent semiconductor CsPbX3 NCs in a film, to reduce the detrimental effect of grain boundary in hindering charge transport. This aspects can be explored in an attempt to improve the efficiency of optoelectronic devices.

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Biography: 1. Abhishek Swarnkar is an integrated MS-PhD student of Department of Chemistry, IISER Pune. He got his B.Sc. in chemistry from Vinoba Bhave University, India. He worked as a Bhaskara Advanced Solar Energy (BASE) research intern in NREL. His major research interest is colloidal semiconductor halide perovskite nanostructures for different kinds of optoelectronic applications. 2. Vikash Kumar Ravi is an integrated MS-PhD student in Department of Chemistry, IISER Pune. He obtained his Bachelor’s degree from BIT Mesra, Ranchi. Currently his focus is on synthesis of perovskite nanomaterials and study of their optical, optoelectronic and electrochemical properties. 3. Angshuman Nag got his Master of Science in Chemistry from IIT Guwahati and carried out his PhD degree from SSCU at IISc Bangalore, India. He then completed two terms as a postdoctoral researcher at IISc Bangalore and University of Chicago. In 2012, He Joined at IISER Pune as a Ramanujan Fellow, and then from 2015 onward, he is continuing as an Assistant Professor in Chemistry.

Author Information: The authors declare no competing financial interests. Acknowledgment:


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A.N. acknowledges Science and Engineering Research Board (SERB) for Ramanujan Fellowship (SR/S2/RJN-61/2012). A.S and V.K.R. acknowledge IISER Pune for PhD fellowship.

References: (1) Pietryga, J. M.; Park, Y.-S.; Lim, J.; Fidler, A. F.; Bae, W. K.; Brovelli, S.; Klimov, V. I. Spectroscopic and Device Aspects of Nanocrystal Quantum Dots. Chem. Rev. 2016, 116, 10513-10622. (2) Kagan, C. R.; Lifshitz, E.; Sargent, E. H.; Talapin, D. V. Building Devices from Colloidal Quantum Dots. Science 2016, 353, 885. (3) Talapin, D. V.; Lee, J.-S.; Kovalenko, M. V.; Shevchenko, E. V. Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications. Chem. Rev. 2010, 110, 389-458. (4) Hines, M. A.; Guyot-Sionnest, P. Synthesis and Characterization of Strongly Luminescing ZnSCapped CdSe Nanocrystals. J. Phys. Chem. 1996, 100, 468-471 (5) Chen, O.; Zhao, J.; Chauhan, V. P.; Cui, J.; Wong, C.; Harris, D. K.; Wei, H.; Han, H.-S.; Fukumura, D.; Jain, R. K. et al. Compact High-Quality CdSe–CdS Core–Shell Nanocrystals with Narrow Emission Linewidths and Suppressed Blinking. Nat. Mater. 2013, 12, 445-451. (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) 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. (8) Yettapu, G. R.; Talukdar, D.; Sarkar, S.; Swarnkar, A.; Nag, A.; Ghosh, P.; Mandal, P. Terahertz Conductivity within Colloidal CsPbBr3 Perovskite Nanocrystals: Remarkably High Carrier Mobilities and Large Diffusion Lengths. Nano Lett. 2016, 16, 4838-4848. (9) ten Brinck, S.; Infante, I. Surface Termination, Morphology, and Bright Photoluminescence of Cesium Lead Halide Perovskite Nanocrystals. ACS Energy Lett. 2016, 1, 1266-1272. (10) Brandt, R. E.; Stevanović, V.; Ginley, D. S.; Buonassisi, T. Identifying Defect-Tolerant Semiconductors with High Minority-Carrier Lifetimes: beyond Hybrid Lead Halide Perovskites. MRS Commun. 2015, 5, 265-275. (11) Yakunin, S.; Protesescu, L.; Krieg, F.; Bodnarchuk, M. I.; Nedelcu, G.; Humer, M.; De Luca, G.; Fiebig, M.; Heiss, W.; Kovalenko, M. V. Low-threshold Amplified Spontaneous Emission and Lasing from Colloidal Nanocrystals of Caesium Lead Halide Perovskites. Nat. Commun. 2015, 6, 8056.


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(12) Song, J.; Li, J.; Li, X.; Xu, L.; Dong, Y.; Zeng, H. Quantum Dot Light-Emitting Diodes Based on Inorganic Perovskite Cesium Lead Halides (CsPbX3). Adv. Mater. 2015, 27, 7162-7167. (13) 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. (14) 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. (15) Gonzalez-Carrero, S.; Galian, R. E.; Pérez-Prieto, J. Organic-Inorganic and All-Inorganic Lead Halide Nanoparticles. Opt. Express 2016, 24, A285-A301. (16) Bai, S.; Yuan, Z.; Gao, F. Colloidal Metal Halide Perovskite Nanocrystals: Synthesis, Characterization, and Applications. J. Mater. Chem. C 2016, 4, 3898-3904. (17) Stoumpos, C. C.; Kanatzidis, M. G. Halide Perovskites: Poor Man's High-Performance Semiconductors. Adv. Mater. 2016, 28, 5778-5793. (18) Manser, J. S.; Christians, J. A.; Kamat, P. V. Intriguing Optoelectronic Properties of Metal Halide Perovskites. Chem. Rev. 2016, 116, 12956-13008. (19) Yang, G.-L.; Zhong, H.-Z. Organometal Halide Perovskite Quantum Dots: Synthesis, Optical Properties, and Display Applications. Chin. Chem. Lett. 2016, 27, 1124-1130. (20) Zhang, Y.; Liu, J.; Wang, Z.; Xue, Y.; Ou, Q.; Polavarapu, L.; Zheng, J.; Qi, X.; Bao, Q. Synthesis, Properties, and Optical Applications of Low-Dimensional Perovskites. Chem. Commun. 2016, 52, 1363713655. (21) Amgar, D.; Aharon, S.; Etgar, L. Inorganic and Hybrid Organo-Metal Perovskite Nanostructures: Synthesis, Properties, and Applications. Adv. Funct. Mater. 2016, 26, 8576-8593. (22) Huang, H.; Polavarapu, L.; Sichert, J. A.; Susha, A. S.; Urban, A. S.; Rogach, A. L. Colloidal Lead Halide Perovskite Nanocrystals: Synthesis, Optical Properties and Applications. NPG Asia Mater. 2016, 8, e328. (23) Ha, S.-T.; Su, R.; Xing, J.; Zhang, Q.; Xiong, Q., Metal Halide Perovskite Nanomaterials: Synthesis and Applications. Chem. Sci. 2017, 8, 2522-2536. (24) Li, X.; Cao, F.; Yu, D.; Chen, J.; Sun, Z.; Shen, Y.; Zhu, Y.; Wang, L.; Wei, Y.; Wu, Y.; et al. All Inorganic Halide Perovskites Nanosystem: Synthesis, Structural Features, Optical Properties and Optoelectronic Applications. Small 2017, 13, 1603996. (25) Filippetti, A.; Mattoni, A. Hybrid Perovskites for Photovoltaics: Insights from First Principles. Phys. Rev. B 2014, 89, 125203. (26) Dag, I.; Lifshitz, E. Dynamics of Recombination Processes in PbI2 Nanocrystals Embedded in Porous Silica Films. J. Phys. Chem. 1996, 100, 8962-8972. (27) Ravi, V. K.; Markad, G. B.; Nag, A. Band Edge Energies and Excitonic Transition Probabilities of Colloidal CsPbX3 (X = Cl, Br, I) Perovskite Nanocrystals. ACS Energy Lett. 2016, 1, 665-671.


Page 23 of 28

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(28) Mittal, M.; Jana, A.; Sarkar, S.; Mahadevan, P.; Sapra, S. Size of the Organic Cation Tunes the Band Gap of Colloidal Organolead Bromide Perovskite Nanocrystals. J. Phys. Chem. Lett. 2016, 7, 3270-3277. (29) Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Bertolotti, F.; Masciocchi, N.; Guagliardi, A.; Kovalenko, M. V. Monodisperse Formamidinium Lead Bromide Nanocrystals with Bright and Stable Green Photoluminescence. J. Am. Chem. Soc. 2016, 138, 14202-14205. (30) Kang, J.; Wang, L.-W., High Defect Tolerance in Lead Halide Perovskite CsPbBr3. J. Phys. Chem. Lett. 2017, 8, 489-493. (31) Tsuji, I.; Kato, H.; Kobayashi, H.; Kudo, A. Photocatalytic H2 Evolution Reaction from Aqueous Solutions over Band Structure-Controlled (AgIn)xZn2(1-x)S2 Solid Solution Photocatalysts with VisibleLight Response and Their Surface Nanostructures. J. Am. Chem. Soc. 2004, 126, 13406-13413. (32) Zakutayev, A.; Caskey, C. M.; Fioretti, A. N.; Ginley, D. S.; Vidal, J.; Stevanovic, V.; Tea, E.; Lany, S. Defect Tolerant Semiconductors for Solar Energy Conversion. J. Phys. Chem. Lett. 2014, 5, 11171125. (33) Rao, M. J.; Shibata, T.; Chattopadhyay, S.; Nag, A. Origin of Photoluminescence and XAFS Study of (ZnS)1–x(AgInS2)x Nanocrystals. J. Phys. Chem. Lett. 2014, 5, 167-173. (34) De Roo, J.; Ibáñez, 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. (35) Jellicoe, T. C.; Richter, J. M.; Glass, H. F. J.; Tabachnyk, M.; Brady, R.; Dutton, S. E.; Rao, A.; Friend, R. H.; Credgington, D.; Greenham, N. C. et al. Synthesis and Optical Properties of Lead-Free Cesium Tin Halide Perovskite Nanocrystals. J. Am. Chem. Soc. 2016, 138, 2941-2944. (36) Eperon, G. E.; Paterno, G. M.; Sutton, R. J.; Zampetti, A.; Haghighirad, A. A.; Cacialli, F.; Snaith, H. J. Inorganic Caesium Lead Iodide Perovskite Solar Cells. J. Mater. Chem. A 2015, 3, 19688-19695. (37) Liu, C.; Fan, J.; Li, H.; Zhang, C.; Mai, Y. Highly Efficient Perovskite Solar Cells with Substantial Reduction of Lead Content. Sci. Rep. 2016, 6, 35705. (38) Akkerman, Q. A.; D’Innocenzo, V.; Accornero, S.; Scarpellini, A.; Petrozza, A.; Prato, M.; Manna, L. Tuning the Optical Properties of Cesium Lead Halide Perovskite Nanocrystals by Anion Exchange Reactions. J. Am. Chem. Soc. 2015, 137, 10276-10281. (39) Nedelcu, G.; Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Grotevent, M. J.; Kovalenko, M. V. Fast Anion-Exchange in Highly Luminescent Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, I). Nano Lett. 2015, 15, 5635-5640. (40) Ramasamy, P.; Lim, D.-H.; Kim, B.; Lee, S.-H.; Lee, M.-S.; Lee, J.-S. All-Inorganic Cesium Lead Halide Perovskite Nanocrystals for Photodetector Applications. Chem. Commun. 2016, 52, 2067-2070. (41) 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.


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Page 24 of 28

(42) Wang, A.; Yan, X.; Zhang, M.; Sun, S.; Yang, M.; Shen, W.; Pan, X.; Wang, P.; Deng, Z. Controlled Synthesis of Lead-Free and Stable Perovskite Derivative Cs2SnI6 Nanocrystals via a Facile Hot-Injection Process. Chem. Mater. 2016, 28, 8132-8140. (43) Zhao, X.-G.; Yang, J.-H.; Fu, Y.; Yang, D.; Xu, Q.; Yu, L.; Wei, S.-H.; Zhang, L. Design of LeadFree Inorganic Halide Perovskites for Solar Cells via Cation-Transmutation. J. Am. Chem. Soc. 2017, 139, 2630-2638. (44) Leng, M.; Chen, Z.; Yang, Y.; Li, Z.; Zeng, K.; Li, K.; Niu, G.; He, Y.; Zhou, Q.; Tang, J. LeadFree, Blue Emitting Bismuth Halide Perovskite Quantum Dots. Angew. Chem., Int. Ed. 2016, 55, 1501215016. (45) Bard A. J.; Parsons, R.; Jordan, J. Standard Potentials in Aqueous Solution; Marcel Dekker: New York, 1985. (46) Hao, F.; Stoumpos, C. C.; Cao, D. H.; Chang, R. P. H.; Kanatzidis, M. G. Lead-Free Solid-State Organic-Inorganic Halide Perovskite Solar Cells. Nat. Photonics 2014, 8, 489-494. (47) Kumar, M. H.; Dharani, S.; Leong, W. L.; Boix, P. P.; Prabhakar, R. R.; Baikie, T.; Shi, C.; Ding, H.; Ramesh, R.; Asta, M. et al. Lead-Free Halide Perovskite Solar Cells with High Photocurrents Realized Through Vacancy Modulation. Adv. Mater. 2014, 26, 7122-7127. (48) Hermann, A.; Furthmüller, J.; Gäggeler, H. W.; Schwerdtfeger, P. Spin-Orbit Effects in Structural and Electronic Properties for the Solid State of the Group-14 Elements from Carbon to Superheavy Element 114. Phys. Rev. B 2010, 82, 155116. (49) Umari, P; Mosconi, E; Angelis, F. D. Relativistic GW Calculations on CH3NH3PbI3 and CH3NH3SnI3 Perovskites for Solar Cell Applications. Sci. Rep. 2014, 4, 4467 (50) Song, T.-B.; Yokoyama, T.; Aramaki, S.; Kanatzidis, M. G. Performance Enhancement of Lead-Free Tin-Based Perovskite Solar Cells with Reducing Atmosphere-Assisted Dispersible Additive. ACS Energy Lett. 2017, 2, 897-903. (51) Song, T.-B.; Yokoyama, T.; Stoumpos, C. C.; Logsdon, J.; Cao, D. H.; Wasielewski, M. R.; Aramaki, S.; Kanatzidis, M. G. Importance of Reducing Vapor Atmosphere in the Fabrication of TinBased Perovskite Solar Cells. J. Am. Chem. Soc. 2017, 139, 836-842. (52) Mudring, A.-V. Thallium Halides – New Aspects of the Stereochemical Activity of Electron Lone Pairs of Heavier Main-Group Elements. Eur. J. Inorg. Chem. 2007, 2007, 882-890. (53) Giustino, F.; Snaith, H. J. Toward Lead-Free Perovskite Solar Cells. ACS Energy Lett. 2016, 1, 12331240. (54) Slavney, A. H.; Hu, T.; Lindenberg, A. M.; Karunadasa, H. I. A Bismuth-Halide Double Perovskite with Long Carrier Recombination Lifetime for Photovoltaic Applications. J. Am. Chem. Soc. 2016, 138, 2138-2141. (55) Savory, C. N.; Walsh, A.; Scanlon, D. O. Can Pb-Free Halide Double Perovskites Support HighEfficiency Solar Cells? ACS Energy Lett. 2016, 1, 949-955. (56) Tong, Y.; Ehrat, F.; Vanderlinden, W.; Cardenas-Daw, C.; Stolarczyk, J. K.; Polavarapu, L.; Urban, A. S. Dilution-Induced Formation of Hybrid Perovskite Nanoplatelets. ACS Nano 2016, 10, 10936-10944. 24 ACS Paragon Plus Environment

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(57) Hintermayr, V. A.; Richter, A. F.; Ehrat, F.; Döblinger, M.; Vanderlinden, W.; Sichert, J. A.; Tong, Y.; Polavarapu, L.; Feldmann, J.; Urban, A. S. Tuning the Optical Properties of Perovskite Nanoplatelets through Composition and Thickness by Ligand-Assisted Exfoliation. Adv. Mater. 2016, 28, 9478-9485. (58) Mitzi, D. B.; Feild, C. A.; Harrison, W. T. A.; Guloy, A. M. Conducting Tin Halides with a Layered Organic-Based Perovskite Structure. Nature 1994, 369, 467-469. (59) Saparov, B.; Hong, F.; Sun, J.-P.; Duan, H.-S.; Meng, W.; Cameron, S.; Hill, I. G.; Yan, Y.; Mitzi, D. B. Thin-Film Preparation and Characterization of Cs3Sb2I9: A Lead-Free Layered Perovskite Semiconductor. Chem. Mater. 2015, 27, 5622-5632. (60) 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. (61) Hamdeh, U. H.; Nelson, R. D.; Ryan, B. J.; Bhattacharjee, U.; Petrich, J. W.; Panthani, M. G. Bismuth Based Hybrid Perovskites A3Bi2I9 (A: Methylammonium or Cesium) for Solar Cell Application. Chem. Mater. 2016, 28, 6567-6574. (62) Ganose, A. M.; Savory, C. N.; Scanlon, D. O. Beyond Methylammonium Lead Iodide: Prospects for the Emergent Field of ns2 Containing Solar Absorbers. Chem. Commun. 2017, 53, 20-44. (63) Fabini, D. H.; Labram, J. G.; Lehner, A. J.; Bechtel, J. S.; Evans, H. A.; Van der Ven, A.; Wudl, F.; Chabinyc, M. L.; Seshadri, R. Main-Group Halide Semiconductors Derived from Perovskite: Distinguishing Chemical, Structural, and Electronic Aspects. Inorg. Chem. 2017, 56, 11-25. (64) Hoye, R. L. Z.; Schulz, P.; Schelhas, L. T.; Holder, A. M.; Stone, K. H.; Perkins, J. D.; Vigil-Fowler, D.; Siol, S.; Scanlon, D. O.; Zakutayev, A. et al. Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations. Chem. Mater. 2017, 29, 1964-1988. (65) McClure, E. T.; Ball, M. R.; Windl, W.; Woodward, P. M. Cs2AgBiX6 (X = Br, Cl): New Visible Light Absorbing, Lead-Free Halide Perovskite Semiconductors. Chem. Mater. 2016, 28, 1348-1354. (66) Volonakis, G.; Filip, M. R.; Haghighirad, A. A.; Sakai, N.; Wenger, B.; Snaith, H. J.; Giustino, F. Lead-Free Halide Double Perovskites via Heterovalent Substitution of Noble Metals. J. Phys. Chem. Lett. 2016, 7, 1254-1259. (67) Naphade, R.; Nagane, S.; Shanker, G. S.; Fernandes, R.; Kothari, D.; Zhou, Y.; Padture, N. P.; Ogale, S. Hybrid Perovskite Quantum Nanostructures Synthesized by Electrospray Antisolvent–Solvent Extraction and Intercalation. ACS Appl. Mater. Interfaces 2016, 8, 854-861. (68) Bekenstein, Y.; Koscher, B. A.; Eaton, S. W.; Yang, P.; Alivisatos, A. P. Highly Luminescent Colloidal Nanoplates of Perovskite Cesium Lead Halide and Their Oriented Assemblies. J. Am. Chem. Soc. 2015, 137, 16008-16011. (69) Hassan, Y.; Song, Y.; Pensack, R. D.; Abdelrahman, A. I.; Kobayashi, Y.; Winnik, M. A.; Scholes, G. D. Structure-Tuned Lead Halide Perovskite Nanocrystals. Adv. Mater. 2016, 28, 566-573. (70) Akkerman, Q. A.; Motti, S. G.; Srimath Kandada, A. R.; Mosconi, E.; D’Innocenzo, V.; Bertoni, G.; Marras, S.; Kamino, B. A.; Miranda, L.; De Angelis, F. et al. Solution Synthesis Approach to Colloidal 25 ACS Paragon Plus Environment

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Page 26 of 28

Cesium Lead Halide Perovskite Nanoplatelets with Monolayer-Level Thickness Control. J. Am. Chem. Soc. 2016, 138, 1010-1016. (71) Ming, W.; Shi, H.; Du, M.-H. Large Dielectric Constant, High Acceptor Density, and Deep Electron Traps in Perovskite Solar Cell Material CsGeI3. J. Mater. Chem. A 2016, 4, 13852-13858. (72) Ravi, V. K.; Swarnkar, A.; Chakraborty, R.; Nag, A. Excellent Green but Less Impressive Blue Luminescence from CsPbBr3 Perovskite Nanocubes and Nanoplatelets. Nanotechnology 2016, 27, 325708. (73) Tong, Y.; Bladt, E.; Aygüler, M. F.; Manzi, A.; Milowska, K. Z.; Hintermayr, V. A.; Docampo, P.; Bals, S.; Urban, A. S.; Polavarapu, L. et al. Highly Luminescent Cesium Lead Halide Perovskite Nanocrystals with Tunable Composition and Thickness by Ultrasonication. Angew. Chem., Int. Ed. 2016, 55, 13887-13892. (74) 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, 86038611. (75) Pradhan, N.; Adhikari, S. D.; Nag, A.; Sarma, D. D. Luminescence, Plasmonic and Magnetic Properties of Doped Semiconductor Nanocrystals: Current Developments and Future Prospects. Angew. Chem., Int. Ed. 2017, DOI: 10.1002/anie.201611526. (76) Norris, D. J.; Yao, N.; Charnock, F. T.; Kennedy, T. A. High-Quality Manganese-Doped ZnSe Nanocrystals. Nano Lett. 2001, 1, 3-7. (77) Pradhan, N.; Goorskey, D.; Thessing, J.; Peng, X. An Alternative of CdSe Nanocrystal Emitters: Pure and Tunable Impurity Emissions in ZnSe Nanocrystals. J. Am. Chem. Soc. 2005, 127, 17586-17587. (78) Santra, P. K.; Kamat, P. V. Mn-Doped Quantum Dot Sensitized Solar Cells: A Strategy to Boost Efficiency over 5%. J. Am Chem. Soc. 2012, 134, 2508-2511. (79) Fainblat, R.; Barrows, C. J.; Hopmann, E.; Siebeneicher, S.; Vlaskin, V. A.; Gamelin, D. R.; Bacher, G. Giant Excitonic Exchange Splittings at Zero Field in Single Colloidal CdSe Quantum Dots Doped with Individual Mn2+ Impurities. Nano Lett. 2016, 16, 6371-6377. (80) 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, 73767380. (81) 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. (82) Liu, H.; Wu, Z.; Shao, J.; Yao, D.; Gao, H.; Liu, Y.; Yu, W.; Zhang, H.; Yang, B. CsPbxMn1–xCl3 Perovskite Quantum Dots with High Mn Substitution Ratio. ACS Nano 2017, 11, 2239-2247. (83) Mir, W. J.; Jagadeeswararao, M.; Das, S.; Nag, A. Colloidal Mn-Doped Cesium Lead Halide Perovskite Nanoplatelets. ACS Energy Lett. 2017, 2, 537-543.


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(84) 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. (85) 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, 40874097. (86) Jiang, Q.; Chen, M.; Li, J.; Wang, M.; Zeng, X.; Besara, T.; Lu, J.; Xin, Y.; Shan, X.; Pan, B.; Wang, C.; Lin, S.; Siegrist, T.; Xiao, Q.; Yu, Z. Electrochemical Doping of Halide Perovskites with Ion Intercalation. ACS Nano 2017, 11, 1073-1079. (87) Wu, K.; Chen, J.; McBride, J. R.; Lian, T., Efficient Hot-Electron Transfer by a Plasmon-Induced Interfacial Charge-Transfer Transition. Science 2015, 349, 632-635. (88) Carretero-Palacios, S.; Jiménez-Solano, A.; Míguez, H. Plasmonic Nanoparticles as Light-Harvesting Enhancers in Perovskite Solar Cells: A User’s Guide. ACS Energy Lett. 2016, 1, 323-331. (89) Balakrishnan, S. K.; Kamat, P. V. Au–CsPbBr3 Hybrid Architecture: Anchoring Gold Nanoparticles on Cubic Perovskite Nanocrystals. ACS Energy Lett. 2017, 2, 88-93. (90) Zhang, X.; Xu, B.; Wang, W.; Liu, S.; Zheng, Y.; Chen, S.; Wang, K.; Sun, X. W. Plasmonic Perovskite Light-Emitting Diodes Based on the Ag–CsPbBr3 System. ACS Appl. Mater. Interfaces 2017, 9, 4926-4931. (91) Lee, B.; Stoumpos, C. C.; Zhou, N.; Hao, F.; Malliakas, C.; Yeh, C.-Y.; Marks, T. J.; Kanatzidis, M. G.; Chang, R. P. H. Air-Stable Molecular Semiconducting Iodosalts for Solar Cell Applications: Cs2SnI6 as a Hole Conductor. J. Am. Chem. Soc. 2014, 136, 15379-15385. (92) Matsushima, T.; Hwang, S.; Sandanayaka, A. S. D.; Qin, C.; Terakawa, S.; Fujihara, T.; Yahiro, M.; Adachi, C. Solution-Processed Organic–Inorganic Perovskite Field-Effect Transistors with High Hole Mobilities. Adv. Mater. 2016, 28, 10275-10281. (93) Labram, J. G.; Fabini, D. H.; Perry, E. E.; Lehner, A. J.; Wang, H.; Glaudell, A. M.; Wu, G.; Evans, H.; Buck, D.; Cotta, R. et al. Temperature-Dependent Polarization in Field-Effect Transport and Photovoltaic Measurements of Methylammonium Lead Iodide. J. Phys. Chem. Lett. 2015, 6, 3565-3571. (94) Lin, C. C.; Meijerink, A.; Liu, R.-S. Critical Red Components for Next-Generation White LEDs. J. Phys. Chem. Lett. 2016, 7, 495-503.


ACS Energy Letters

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Quotes to be highlighted in the manuscript

1. Colloidal metal halide NCs containing tin (Sn), germanium (Ge), Indium (In) bismuth (Bi) and antimony (Sb) can be explored as a replacement for Pb halides. 2. Doping metal ions into the lattice of a semiconductor NC provide interesting properties by combining the effects of both quantum confinement and dopant ions. 3. Metal-semiconductor heterostructure at nanoscale are interesting for photocatalysis and optoelectronic applications. 4. Clearly, the computational studies and synthesis of bulk metal halides, suggest interesting possibilities for preparing new colloidal Cs2M+M3+X6 NCs.


Beyond Colloidal Cesium Lead Halide Perovskite Nanocrystals

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