Lead-Free Halide Perovskites and Perovskite Variants as Phosphors

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Lead-Free Halide Perovskites and Perovskite Variants as Phosphors toward Light-Emitting Applications Jiajun Luo, Manchen Hu, Guangda Niu, and Jiang Tang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b08407 • Publication Date (Web): 19 Aug 2019 Downloaded from pubs.acs.org on August 19, 2019

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ACS Applied Materials & Interfaces

Lead-Free Halide Perovskites and Perovskite Variants as Phosphors toward Light-Emitting Applications Jiajun Luo,† Manchen Hu,† Guangda Niu, *,† and Jiang Tang*,† †Sargent

Joint Research Center, Wuhan National Laboratory for

Optoelectronics (WNLO) and School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, 430074, China

1 ACS Paragon Plus Environment

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ABSTRACT: Lead halide perovskites have attracted tremendous research interests in the light-emitting society owing to their high defect-tolerance, solution-processability, tunable spectrum and efficient emission. In terms of luminescence types, both the narrowband emission derived from free-exciton and broadband white light emission from self-trapped exciton (STE) show great advantages in the light-emitting applications. Despite the fascinating characteristics, their commercialization still suffers from the presence of toxic lead (Pb) and unsatisfactory stability. In this spotlight, we mainly focus on the lead-free candidates as phosphors for possible light-emitting applications. Thanks to the chemical diversity of metal halide perovskites and perovskite variants, many excellent lead-free light-emitting materials have recently been synthesized and characterized. We firstly classify these materials into three types according to material structures, including 1) double perovskites A2B(I)B(III)X6, 2) vacancy ordered perovskites A2B(IV)X6, 3) miscellaneous perovskite variants or halide semiconductors, which refer to halides without clear relation to the perovskite structure. Then we highlight the importance of electronic dimensionality, defects passivation and impurity doping in developing highly efficient perovskite-based emitters. We also discuss their applications in white light emitting diodes (W-LED). Further challenges towards practical


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applications and potential applications are also included in a section on outlook and future challenges.

KEYWORDS: lead-free • perovskite • electronic dimensionality • defects

passivation • white light-emitting diodes

INTRODUCTION Since lighting and displays consume over 20% of worldwide electric energy every year, energy efficiency is essential in the field of illumination1. Phosphorconverted light-emitting diodes (LEDs) have attracted substantial attention in industry and academia because of their low power consumption, superior luminous efficacy, environmental friendliness, long duration and highly tunable optical properties2-5. The rare-earth based phosphors in combination with the blue-to-violet InGaN/GaN chip have become mainstream6, 7. However, the rareearth elements also face many problems, such as supply shortage and recycle difficulty8. As possible alternatives, organic phosphors may undergo photobleaching at a relatively high temperature9, and metal nanoclusters (NCs) suffer from the complicated synthesis process10. Thus, it is of great interest to explore new phosphor materials excited by blue-to-violet InGaN/GaN chip. Recently, metal halide perovskites have gained great research interest in the lightemitting society due to their high photoluminescence quantum yield (PLQY), highly tunable emission across the entire visible spectrum and low-cost solution 3 ACS Paragon Plus Environment


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processability11-15. Specifically, Zhou et al. demonstrated the in situ fabrication of MAPbX3 (X= Cl, Br, I) nanocrystals (NCs) embedded polyvinylidene fluoride (PVDF) composite films with tunable emission range from 440 nm to 730 nm, and these films also exhibited high PLQY (about 94.6%) as well as excellent stability against ultraviolet light and moisture, showing great potential in lighting and displays applications12. Besides the narrowband emission in halide perovskites, Karunadasa and coworkers firstly observed intrinsic, broadband white-light emission from layered lead halide perovskites, originating from exciton self-trapping16-20. A single material with broadband white emission covering the entire visible spectrum is ideal for lighting application, because it can avoid the self-absorption and color instability problems in mixed and multiple emitters21-23. Despite the rapid advances of lead halide perovskites in light-emitting applications, the commercialization of these emerging technologies still suffer from two formidable issues, the inclusion of toxic lead and unsatisfactory stability24-26. Since lead halide perovskites are highly soluble in water and lead poisoning is recognized as a major public health risk, lead substitution is of great significance if their outstanding performance could be retained. Thanks to the rich structures and elements of perovskite family, various lead-free halide perovskites with extraordinary optical properties have been developed and characterized in recent years. Bi(III)-, Sb(III)-, In(III)-, Cu(I)-, Cu(II)-, Sn(IV)-,


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Sn(II)- and Mn(II)- based lead-free perovskites or perovskite variants show efficient emission27-43 (Table 1), which are comparable with Pb-based perovskites or even better in some aspects. These encouraging results will inspire more excellent work in the field of lead-free light-emitting perovskites. Meanwhile, electronic dimensionality, defects passivation and impurity doping are recognized as essential factors in achieving efficient perovskite light emitters. Firstly, Xiao et al. theoretically introduced the concept of electronic dimensionality to better explain the optoelectronic properties compared to the structural dimensionality44. The three-dimensional electronic network may give rise to large band dispersion, enabling excitons to dissociate readily without radiative recombination, thus materials with low electronic dimensionality are generally expected to own relatively high PLQY26. As an example, Zhou et al. reported single crystalline bulk assemblies of 0D structured materials as hostguest systems, and the light emitting species were periodically embedded in a host

matrix

without

electronic

band

connection42.

The

as-prepared

(C4N2H14X)4SnX6 (X = Br or I) and (C9NH20)2SbX5 (X = Cl) exhibited the nearunity PLQY. Besides, the electronic dimensionality was also highly related to the formation of STEs45. Wang et al. theoretically evaluated the STEs formation and found out that the low electronic dimensionality was generally required for STEs formation45. Secondly, defects states, especially the deep defects states, can serve as recombination centers and cause PL loss. Defects passivation is



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thus an effective way to improve the PLQY. Elements doping or alloying is widely used for defects passivation in halide perovskite materials46. As an example, Stranks et al. reported a potassium passivated halide perovskite films with external photoluminescence quantum yields of 66%, which translated to the internal yields of over 95%47. Lastly, it is of great interest to introduce new emission states in perovskites by doping or alloying. Parobek et al. and coworkers reported the one-pot synthesis of Mn doped CsPbX3 perovskite nanocrystals and realized strong luminescence from Mn2+ ions48. Benefitting from the efficient quantum cutting emission process, Zhou et al. realized a 146% internal luminescent quantum yield by doping cerium and ytterbium into CsPbBr1.5Cl1.5 quantum dots (QDs)49. These works highlighted the impurity doping as an effective way to adjust the optoelectronic properties and develop new functions for halide perovskites. In this review, we firstly classify the lead-free halide perovskite light emitting materials into three types according to their structures (Fig. 1), and we highlight the importance of low electronic dimensionality, defects passivation and impurity doping in developing highly efficient perovskite-based emitters. We then discuss their applications in white light emitting diodes, and last, we comment on the challenges towards practical applications for these halide perovskites.


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Figure 1. Four representative lead-free perovskite structures. Crystal structures of (a) double perovskites Cs2Ag(I)Bi(III)Br650 (b) vacancy ordered perovskites Cs2Sn(IV)I651 (c) Bi(III) based perovskite variant Cs3Bi(III)2Br928, (d) Cu(I) based perovskite variant Cs3Cu(I)2I537. Table 1. The photoluminescence properties and synthesis method of light emitting lead free perovskites and perovskite variants chemical formula

Emission

peak PLQY (%)

Synthesis method

ref

(nm) MA3Bi2(Cl,Br)9 QDs

422

54.1

Co-LARP

27

Cs3Bi2Br9 QDs

410

19.4

Co-LARP

28

Cs3Sb2Br9 QDs

410

46

Co-LARP

29



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PEA2SnI4

620

6.4

Solution method

30

(C18H35NH3)2SnBr4

88

88

Solution method

31

(octylammonium)2SnX4 600

~100

Solution method

32

Cs2SnCl6: Bi3+

454

78.9

Hydrothermal

33

Cs2SnCl6: Sb3+

602

37

Hydrothermal

34

Cs2Ag0.6Na0.4InCl6

565

86

Hydrothermal

35

Cs2AgIn0.875Bi0.125Cl6

585

70.3

Hydrothermal

36

Cs3Cu2I5

445

91.2

Solution method

37

Cs4SnBr6

540

15

Solid state reaction

38

Cs2InBr5·H2O

695

33

Solution method

39

Cs2CuBr4 QDs

393

37.5

LARP

40

Cs2CuCl4 QDs

388

51.8

LARP

40

Rb7Bi3Cl16

437

28.4

Hydrothermal

41

(C4N2H14Br)4SnBr6

570

95

Solution method

42

(C4N2H14I)4SnI6

620

75

Solution method

42

(C9NH20)2SbCl5

590

98

Solution method

42

[PPh4]2[MnBr4]

~520

98

Solution method

43

Note: Co-LARP stands for collaborative solvent ligand-assisted re-precipitation; LARP stands for ligand-assisted re-precipitation.

Double perovskites A2B(I)B(III)X6


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Double perovskites, which were initially called “elpasolites” structure, recently demonstrated as a promising alternative to lead halide perovskites. The representative crystal structure of double perovskite is shown in Fig. 1a, indicating a facet-centered cubic structure with space group Fm3m, and their three-dimensional structure is maintained while Pb2+ is replaced by less toxic monovalent and trivalent cations. Since the report of Cs2AgBiX6 (X=Cl, Br) in 201650, 52, tremendous progress has been achieved in synthesizing new leadfree halide double perovskites and theoretical understanding of their optoelectronic properties44, 53-60. For example, Xiao et al. pointed out halide double perovskites generally exhibited larger carrier effective mass and lower carrier mobility compared to that of Pb based perovskites44. Taking Cs2AgBiBr6 for example, theoretical calculations revealed the VBM was mainly derived from Ag 4d-Br 5p antibonding states while the CBM was mainly derived from Bi 6p-Br 4p bonding states. Thus, the wave function of holes and electrons were confined at [AgBr6] and [BiBr6] octahedra respectively, which explain the low carrier mobility and larger carrier effective mass. This work highlight the electronic dimensionality rather than structural dimensionality determines the optoelectronic properties of halide perovskites.



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Figure 2. (a) The band structure of Cs2AgInCl6. The green, blue, cyan and red colors denote the Cl 3p, Ag 4d, In 5s and Ag 5s orbitals, respectively. The same parity at G point indicated parity forbidden transition. (b) Configuration coordinate diagram for the STE formation. Est, Ed and EPL are the selftrapping, lattice-deformation and emission energies, respectively. (c) Parity change of the electron wavefunction after Na alloying. (d) Configuration showing the strengthened STE confinement by the surrounding NaCl6 octahedra. (e) Transient absorption spectra of Cs2Ag0.60Na0.40InCl6. ΔA/A is the optical density. Reprinted by permission from Macmillan Publishers, Nature35, Copyright (2018).


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Double perovskite Cs2AgInCl6 with relatively low electronic dimensionality was recently proposed as a promising material emitting warmwhite light considering its broad spectrum (400- 800 nm) and its all-inorganic nature35, 36. Similar with Cs2AgBiBr6, the VBM was mainly derived from Ag 4dCl 3p orbitals whereas the CBM was mainly derived from delocalized In 5s states, indicating the wave function of holes was strongly confined at [AgCl6] octahedral. As mentioned by Wang et al.45, strong exciton-phonon coupling and low electronic dimensionality were beneficial for the formation of STEs, and STE emission is responsible for the broad spectrum of Cs2AgInCl6. After excitation, holes was quickly trapped at [AgCl6] octahedra and change the electronic configuration of silver from 4d10 to 4d9, causing a strong Jahn-Teller distortion of AgCl6 octahedron. In the self-trapping process of STEs, the selftrapping energy Est and lattice deformation energy Ed were the corresponding energy differences between ground-state and excited-state. Thereby, the emission energy could be calculated to be EPL=Eg-Eb-Est-Ed (Eb is the lowest exction binding energy) (Fig. 2b), which was the origin of the large stokesshift. Furthermore, the electronic dimensionality of Cs2AgInCl6 can be tuned by engineering chemical compositions. Na cation with a similar ionic radius but a distinctively different electronic configuration to Ag was incorporated into the Cs2AgInCl6 lattice. The effect of Na incorporation was twofold. Firstly,



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introducing Na breaks the inversion symmetry of the Cs2AgInCl6 lattice, resulting in change of the parity of the electron wave function and enabling radiative recombination (Fig. 2c). Secondly, although the hole wave function of the STE in Cs2AgInCl6 was localized, the electron wave function was rather spread, leading to the small overlap between hole wave function and electron wave function. Since Na cations contributed to neither conduction band minimum (CBM) nor valence band maximum (VBM) of the alloy, they served as quantum wells to confine the spatial distribution of the STE, especially the electron wave function, enhancing radiative recombination (Fig. 2d). Besides, trace Bi3+ was further introduced to passivate defects and depresses non-radiative recombination loss. Meanwhile, Bi doping could introduce a shallow state and promote exciton localization, similar with the STE emission from I-doped AgBr61. The optimal sample reached an impressive PLQY of about 86% for the white emission. The STE emission mechanism was further experimentally confirmed via transient absorption spectrum (Fig. 2e). A broadband photo-induced absorption at energies across the visible spectrum was observed, indicating the formation of STE states upon excitation. The exciton self-trapping time is estimated to be about 500 fs, which was close to the calculated results based on the phonon energy (τ= 2π/ Ω, Ω is phonon energy). Further evidence was provided by excitation power dependent emission intensity, and the linear relationship instead of saturation at high excitation power ruled out the defects emission.


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Figure 3. (a) The comparison of luminosity function (dashed line) and PL spectra (solid lines) of Cs2Ag0.60Na0.40InCl6, and the PL spectra recorded at different temperatures from 233 K to 343 K. (b) Photoluminescence stability against continuous heating. (c) Operational stability of Cs2Ag0.60Na0.40InCl6 under UV light excited. (d) The XRD results of a double perovskite film (up) and powder (below). The inset shows a photograph of pure quartz substrate, 300-nm thick and 500-nm-thick double perovskite films under 254-nm wavelength UV light excitation. Reprinted by permission from Macmillan Publishers, Nature35, Copyright (2018).



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For lighting application, Cs2Ag0.60Na0.40InCl6 powder not only enjoyed a high overlap with the sensitivity of the human eye to optical wavelengths (luminosity function) (Fig. 3a) but also exhibited a high stability against heat and UV irradiation (Fig. 3b-c). The strongly bound excitons and nearly defectfree lattice prevent photoluminescence quenching of Cs2Ag0.60Na0.40InCl6. The as-prepared W-LED based on the commercial LED chip showed the commission international de L’Eclarage (CIE) coordinates of (0.396, 0.448) with a correlated color temperature (CCT) of 4054 K. It can be seen that double perovskites offer an ideal platform for elements substitutions. McQueen et al. also designed indirect-to-direct bandgap transitions in Cs2Ag(In,Sb)Cl6 double perovskite54. Upon substitution of In by Sb, the character of conduction band minimum change from s-orbital derivation to p-orbital derivation, indicating the lone-pair effects play a crucial role in material designing. In parallel, double perovskite nanocrystals were also synthesized and characterized. The synthetic methods are similar with those used in the lead halide system62. The pure Cs2AgInCl6 NCs exhibited a broad white PL spectrum with PLQY of 1.6% while the Mn(II) ions doped Cs2AgInCl6 NCs demonstrated a typical broad orange PL emission (λem = 620 nm) from Mn(II) and PLQY of 16±4%63. Lee et al. further incorporated rare earth element ytterbium (Yb) into Cs2AgInCl6 NCs and observed infrared emission originated 14 ACS Paragon Plus Environment

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from the f-f transition64. Yang et al. also reported Cs2AgInxBi1-xCl6 NCs with the highest PLQY of 36.6% at 10% Bi content65. These findings further expand chemical diversity and functionality of lead-free double perovskites. Vacancy ordered A2B(IV)X6 Sn(II) and Ge(II) are the most obvious candidates for Pb replacement due to the same valence and similar electronic configuration. However, Sn(II) and Ge(II) tend to be oxidized because of the high-lying ns2 states, resulting in high defects density. Meanwhile, B(IV) based perovskite variants (A2B(IV)X6) exhibit much higher stability due to the B element with stable +4 oxidation state66. The crystal structure of A2B(IV)X6 is derived from traditional perovskites structure by removing half of the octahedral B(IV) atoms (Fig. 1b). The [BX6]2- octahedra are isolated by the Cs+ cations (Fig. 1b), which may provide a quantum confinement and enhance the photoluminescence.



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Figure 4. (a) The PLQY results of Cs2SnCl6: xBi with different Bi content. Insets show the photographs of Cs2SnCl6: xBi upon 365 nm light illumination. (b) CIE coordinates of W-LED device. Panels a-b are reprinted from ref33 with permission from John Wiley & Sons Ltd. (c) Absorption spectrum of Cs2SnCl6: 0.59%Sb. Insets show the images of Cs2SnCl6:0.59%Sb under the ambient light and UV light, respectively. (d) CIE coordinates and CCTs of W-LED. Panels c-d are reprinted from ref34 with permission from 2019 Springer Nature. In our previous study, we successfully introduced Bi3+ as the luminescent dopant into lead-free perovskite Cs2SnCl6 host to realize stable, efficient blue


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emission. The Bi3+ replaced Sn4+ heterovalently to preserve the Cs2SnCl6 crystal structure. With the careful optimization of Bi3+ ratio, Cs2SnCl6: 2.75%Bi exhibited strong deep blue emission with 78.9% PLQY upon 365 nm UV light excitation (Fig. 4a), and the emission spectra of the Cs2SnCl6: Bi showed a peak around 454 nm with a wide FWHM of 66 nm and a large Stokes shift of 90 nm. The negligible shift of wavelength dependent PLE and PL spectra and wide excitation plateaus both indicated the light emission mechanisms should not be Bi3+ ionoluminescence. A more plausible explanation was given by the theoretical calculations, and the [BiSn+VCl] defect complex is proposed as the luminescent center. Stability against moisture was evaluated by immersing Cs2SnCl6: Bi samples in deionized water. The PL intensity maintained 97.1% of the initial value after 120 mins soaking due to the formation of BiOCl on the surface of Cs2SnCl6: Bi. In a real W-LED device, Cs2SnCl6:2.75% Bi and commercial yellow phosphor Y3Al5O12:Ce3+ (YAG) were mixed with curable resin, and the as-prepared resin was coated onto a 365 nm wavelength UV chip. The W-LED exhibited a CIE coordinate of (0.36, 0.37) with a correlated color temperature of 4486 K (Fig. 4b), demonstrating its potential applications for lighting. Similar phenomenon was also observed in Sb3+ doped Cs2SnCl6 (Fig. 4c), a broadband orange-red phosphor was obtained with ~37% PLQY at 0.59% Sb doping concentration45. The Cs2SnCl6:0.59%Sb, Cs2SnCl6:2.75%Bi and Ba2Sr2SiO4:Eu2+ based W-LED exhibited a CIE coordinate of (0.30, 0.37) and the color rendering index (CRI) of 81 (Fig. 4d). 17 ACS Paragon Plus Environment


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Perovskite variants As pointed out by Breternitz et al.67, a material must obey three major points to be called a perovskite: (1) the molar ratio of A: B: X should be 1: 1: 3; (2) the B-cation coordination is octahedral or distorted octahedral; (3) the [BX6] octahedra is organized in an all-corner sharing 3D network. Bi based Cs3Bi(III)2X9 (Fig. 1c) and Cu based Cs2Cu(I)I5 (Fig. 1d) are not strictly perovskite materials according to this standard. Thereby, perovskite variants or halide semiconductors here refer to halides without clear relation to the perovskite structure. Perovskite variants or halide semiconductors are recently a hot topic in the research society. Bi(III)-, In(III)-, Cu(I)-, Sb(III)-, Sn(IV)-, Sn(II)- and Mn(II)based perovskite variants have recently been reported with excellent optical properties. Here, we focus on a few of them as examples. First of all, Bi3+ and Sb3+ based perovskite variants are recognized as one of the most promising candidates among lead free perovskites and perovskite variants due to the similar ns2 electronic configuration with Pb. From the structure point of view, the A3B(III)2X9 crystal structure is derived from traditional perovskites structure by removing every third B(III) layer along to achieve charge balance (Fig. 1c). The removed B(III) layer can be viewed as vacancy, and the resulting structures are two-dimensional layered perovskite variants with trigonal P3m1 symmetry29. It is noted that the symmetry may be 18 ACS Paragon Plus Environment

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changed with the different A and X sites, for example, Cs3Bi2I9 and Cs3Bi2Br9 show the trigonal P3m1 symmetry while Rb3Bi2I9 and Cs3Bi2Cl9 shows the monoclinic P21/n symmetry32,68. These structures both exhibit a lower electronic dimensionality compared to three-dimensional cubic perovskite structure, probably resulting in strong phonon-electron coupling, which will be discussed later.

Figure 5. (a) The photograph of MA3Bi2(Br,Cl)9 QDs upon 365 nm light illumination. (b) The schematic illustration of Cl- passivation. (c) Absorption and PL spectra of MA3Bi2(Br,Cl)9 QDs solution. (d) PL decay curves and their fitting results of MA3Bi2(Br,Cl)9 QDs solution. Reprinted with permission from Ref27 Copyright 2018 American Chemical Society. In our previous study, MA3Bi2X9 (X=Cl, Br, I) quantum dots (QDs) were firstly synthesized by a collaborative solvent ligand-assisted re-precipitation (Co19 ACS Paragon Plus Environment


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LARP) method69. With the optimization of precursor solution concertation, MA/Bi molar ratio and reaction temperature, the optimal MA3Bi2Br9 QDs exhibited a PLQY of 12%. Since one of the main origins for PLQY loss is associated with dangling bonds on QD surface, surface passivation was regarded as important approach to remove the dangling bonds and improve photoluminescence. Benefiting from the distinct crystal structure of MA3Bi2Br9 and MA3Bi2Cl9, we continued to optimize the PLQY of MA3Bi2Br9 QDs by an effective Cl- passivation strategy (Fig. 5b). The synthesis of MA3Bi2(Cl, Br)9 QDs followed the same Co-LARP method except for the partially replacing MABr with MACl in the precursor solution. With the optimization of Cl- content, the 33% Cl- content MA3Bi2(Cl, Br)9 QDs exhibited a bright blue emission at wavelength 422 nm with high PLQY of 54.1% (Fig. 5a), which was the maximum among lead free perovskite QDs in the blue- or deep blue-emitting region. The monoexponentially fitted decay with a short lifetime of 2.17 ns was also observed in 33% Cl- passivated sample (Fig. 5d), indicating the perfect passivated surface. Besides, Cl- passivated MA3Bi2Br9 QDs showed a smaller stokes shift and the same emission peak position compared to pure MA3Bi2Br9 QDs, indicating that the Cl- anions mainly located on the surface for the passivation, which could be explained by the incompatible crystal structures between MA3Bi2Br9 and MA3Bi2Cl924.


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Figure 6. (a) Thermogravimetric curves of Cs3Bi2Br9 and MA3Bi2Br9. (b) The stability against deionized water of Cs3Bi2Br9 and MA3Bi2Br9 QDs. (c) Photograph of Cs3Bi2Br9 QD/silica film on quartz, (d) Photograph of Cs3Bi2Br9 QDs/silica composite under ambient light, (e) Photograph of Cs3Bi2Br9 QDs/silica composite UV light. (f) The emission spectrum of the Cs3Bi2Br9 QDs and YAG based W-LED. Inset show the photographs of device with off and on, respectively. (g) The CIE coordinates of Cs3Bi2Br9 QDs, YAG, and WLED, respectively. Reprinted with permission from Ref28 Copyright 2018 American Chemical Society.



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However, the unsatisfactory water stability of MA3Bi2(Cl, Br)9 QDs may restrict their practical application. All-inorganic perovskites generally exhibited higher thermal stability, less moisture sensitivity compared to hybrid organicinorganic perovskites. Yang et al. firstly reported the synthesis and characterization of Cs3Bi2X9 nanocrystals (NCs)70. The typical ligand-free Cs3Bi2Br9 NCs exhibited blue emission at 468 nm wavelength with low PLQY of 0.2 %, and a sudden increase of PLQY to 4.5% was achieved by adding oleic acid for surface passivation. Recently, our group also reported the synthesis of Cs3Bi2X9 QDs by using ethanol as green antisolvent32. The assynthesized Cs3Bi2Br9 QDs exhibited a blue emission at 410 nm wavelength with a PLQY of 19.4%. According to thermogravimetric analysis (TGA) results, Cs3Bi2Br9 exhibited a decomposition temperature of 496 ℃, much higher than that of MA3Bi2Br9 (200 ℃) (Fig. 6a). Moreover, the self-passivation of the hydrolysis product BiOBr were observed when the Cs3Bi2Br9 QDs were exposed to moisture (Fig. 6b). Thanks to the excellent stability and robustness of Cs3Bi2Br9 QDs, we simply mixed tetraethyl orthosilicate (TEOS) and Cs3Bi2Br9 QDs in deionized water to form QDs-silica gel (Fig. 6c-e), and we further demonstrated a white LED (W-LED) by combining Cs3Bi2Br9 QDssilica gel with commercially available YAG (Fig. 6f). The CIE coordinates of W-LED was measured to be (0.29, 0.30), which was close to the standard white light (0.33, 0.33) (Fig. 6g). This finding indicated that the Cs3Bi2Br9 QDs were promising for lighting applications. 22 ACS Paragon Plus Environment

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In parallel, Sb contained perovskite variants Cs3Sb2I9 and Rb3Sb2I9 NCs were also synthesized by Nag et al.71. Followed by this work, Cs3Sb2Br9 NCs with high blue luminescent (PLQY up to 46%) were obtained by Co-LARP method. Such a high PLQY may attribute to the Br-rich surface and high exciton binding energy29. From stability point of view, all-inorganic perovskite variant NCs generally exhibit better stability compared to the organic-inorganic counterpart. On one hand, the decomposition temperature is much higher due to the absence of organic component. On the other hand, all-inorganic perovskite and perovskite NCs can be self-passivated by the hydrolysis product on the surface against moisture. However, these all-inorganic perovskite variant NCs are still not able to survive long-term air exposure, which is still far from meeting the industrial standard. It was noted that A3B(III)2X9 QDs exhibit wider full width at half maximum (FWHM) in photoluminescence spectra and larger stokes shift compared to MAPbX3 QDs, which may undermine their color purity. Similar phenomenon was also observed in bulk A3B(III)2X9 materials. McCall et al. demonstrated that these materials can form self-trapped excitons (STEs) in the excited states68, where excitons are trapped in a state with the assistance of strong electron−phonon coupling. Photoluminescence derived from STE states generally exhibited larger FWHM and more Stokes shift compared to free 23 ACS Paragon Plus Environment


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exciton (FE) states. In A3B(III)2X9 QDs, the relatively wide FWHM should also be originated from the strong electron-phonon coupling72, 73.

Figure 7. (a) The PL and PLE spectra of the Cs3Cu2I5 film. Inset: Photograph of Cs3Cu2I5 film upon the 254 nm light illumination. (b) Photograph of Cs3Cu2I5, a yellow phosphor, and its mixture upon the 254 nm light illumination. (c) CIE coordination. Panels a-c are reprinted with permission from ref37 Copyright 2018 John Wiley & Sons Ltd. (d) The zero dimensional crystal structure of (C4N2H14Br)4SnBr6 . (e) The emission spectra of W-LED. Panels d-e are reprinted with permission from ref42 published by 24 ACS Paragon Plus Environment

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Royal Society of Chemistry. (f) Photographs of Cs4-xAxSn(Br,I)6 (A= K, Rb) powders upon the 365 nm light illumination. Panels f are reprinted with permission from ref38 published by John Wiley & Sons Ltd. (g) The PLE and PL spectra of Cs2InBr5·H2O crystal. (h) Photographs of Cs2InBr5·H2O crystals under ambient light and UV light, respectively. (i) Photographs of hydrated and dehydrated materials, which are embedded into an etched butterfly pattern. Panels g-i are reprinted with permission from ref39 published by John Wiley & Sons Ltd. Another family of Cu based perovskite variants have also been reported recently. Cs3Cu2I5 was reported as a nontoxic all-inorganic halide 0D material with efficient broad blue emission (PLQY up to 90%). The crystal structure of Cs3Cu2I5 belonged to the orthorhombic space group of Pnma. As shown in Fig. 1d, 0D photoactive site of [Cu2I5]3- was isolated by the Cs+ ions, indicating low electronic dimensionality. The large stokes shift was observed by the huge difference between PLE and PL peak (λex = 290 nm, λem = 445 nm) (Fig. 7a), which could be explained by the excited-state structural reorganization. After excitation, Cu(I) changed the electronic configuration from 3d10 to 3d9, favoring the Jahn-Teller distortion, similar with Ag in Cs2AgInCl6. The W-LED was demonstrated by mixing Cs3Cu2I5 powder with a yellow phosphor into polydimethylsiloxane (PDMS) matrix. The as-prepared W-LED exhibited a linear tunable CIE coordinates from (0.15 0.09) to (0.44



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0.48) by simply varying the mixing ratio. Meanwhile, mixed halogen Cs3Cu2Br5−xIx (0 ≤ x ≤ 5) with near-unity PLQY were also reported by Roccanova et al., exhibiting bright blue emission in 456 to 443 nm wavelength range74. For Sn(II) based perovskite variants, Ma et al. firstly reported (C4N2H14Br)4SnBr6 with a near unity PLQY, and the [SnBr6]4- is completely isolated by the organic component (Fig. 7d), forming the “host-guest” system, which the light emitting species are embedded in organic matrix42. The W-LEDs were further demonstrated by blending the (C4N2H14Br)4SnBr6 with blue phosphor, exhibiting a CIE coordinated of (0.35,0.39) and a CCT of 4946K (Fig. 7e). Following this work, Sn(II) based two dimensional perovskite variants (C18H35NH3)2SnBr4 exhibited an impressive high PLQY of 88% with emission wavelength

at

625

nm31.

More

recently,

highly

luminescent

(octylammonium)2SnX4 perovskite variant were reported with a near-unity PLQY in the solid state32, and their broad yellow emission covering the red region exhibited higher CRI in W-LEDs compared to the traditional yellowemitting phosphor YAG, showing great potential as yellow phosphor for nextgeneration display technology. All inorganic zero dimensional material Cs4SnBr6 was also reported to exhibit broadband PL with PLQY of 15% at room temperature, and the PL spectrum was highly tunable by partially substituting the A (Cs, Rb, K) and X 26 ACS Paragon Plus Environment

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(Br, I) sites (Fig. 7f)38. Further DFT analysis exhibited STEs were responsible for the broadband emission and large stokes shift. Cs2InBr5·H2O was another highly luminescent perovskite variant. Similarly, Cs2InBr5·H2O exhibited a 0D crystal structure because InBr5O octahedrons were spatially isolated by two Cs+ ions. The PLE and PL peak located at 355 nm and 695 nm, respectively (Fig. 7g). Interestingly, Cs2InBr5·H2O was further demonstrated as PL water sensor. Cs2InBr5·H2O exhibited different PL wavelength and intensity exposed to different humid air (Fig. 7i), and the response speed was superior to that of other all-inorganic materials. This work further broadened the applications of novel lead-free metal halide perovskite and perovskite variants. Inspired by these works, many luminescent perovskite variants have recently been synthesized and characterized, such as CsCuBr275, and Rb7Bi3Cl1641 etc. Table 2. The CIE coordinate, CCT and CRI of lead free perovskites based WLEDs chemical composition

CIE

CCT (K) CRI

ref

0.29,0.30

8477

/

28

(octylammonium)2SnX4 0.33,0.26

5635

81

32

4486

/

33

coordinate Cs3Bi2Br9 QDs & YAG

& BaMgAl10O17:Eu2+ & G2762 Cs2SnCl6: Bi3+

0.36,0.37



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& Ba2Sr2SiO4:Eu2+ & GaAlSiN3:Eu2+ Cs2SnCl6: Sb3+

0.30,0.37

6815

/

34

Cs2Ag0.6Na0.4InCl6

0.40,0.45

4054

/

35

Cs3Cu2I5

From

/

/

37

& yellow phosphor

0.15,0.09

4946

70

42

& Ba2Sr2SiO4:Eu2+ & Cs2SnCl6: Bi3+

to

0.44,0.48 (C4N2H14Br)4SnBr6

0.35,0.39

& BaMgAl10O17:Eu2+

CONCLUSION AND OUTLOOK In summary, we have reviewed the possible lead-free perovskites and perovskite variants for light-emitting applications, and discussed their structure, properties and applications as phosphors. Firstly, replacing Pb with heterovalent nontoxic elements such as Sb, Bi, Sn and Te generally decreases the electronic dimensionality, which may increase the possibility of STE formation, and large stokes shift and broad PL spectra are commonly observed in such lead-free halide perovskites and perovskite variants. Secondly, the electronic dimensionality is crucial in developing efficient phosphors. Synthesizing quantum dots, introducing impurity doping to form host-guest 28 ACS Paragon Plus Environment

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system and inserting insulating units (such as [NaCl6] in Cs2AgInCl6) are widely used in controlling the electronic dimensionality for halide perovskites. Thirdly, since defects states, especially the deep defects states, can serve as recombination centers and cause PL loss, the passivation is another important factor in developing efficient phosphors. Benefitting from the diverse chemical range of compositions in A, B, X sites, it is easy to find a suitable element doping or alloying to passivate defect states, as illustrated in Cl- passivated MA3Bi2Br9 QDs and Bi3+ passivated Cs2Ag0.60Na0.40InCl6. Finally, all-inorganic metal halide perovskites and perovskite variants are more desirable in practical applications owing to their higher stability against heat and moisture. It is noted that the formation of self-passivated hydrolysis product, such as BiOBr and BiOCl can significantly increase their stability. Although these results are encouraging, there is still tremendous work to be done. Firstly, the lead-free perovskites and perovskite variants based W-LEDs are still far from industrial requirements76, 77. Especially for indoor illumination applications, W-LEDs are required to provide warm enough CCT (80, ideal >90). Besides, the emission intensity of phosphors is required to maintain almost 90% of their initial value after 10,000 hours’ operation, which can be hardly achieved by perovskites and perovskite variants at current stage. Secondly, the PLQY is the basic criterion for light-emitting applications, however, the majority of lead-free perovskites and perovskite



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variants can hardly exceed 80% PLQY. Thirdly, further mechanism understanding and designing principles are still lacking, and we are not able to rationally synthesize new luminescent lead-free perovskites and perovskite variants or freely control their emission spectra. Finally, most of the current work focuses on the photoluminescence LEDs (Table 2), and utilizing these leadfree perovskites and perovskite variants for fabricating electroluminescent devices and tunable lasers remains challenging. Benefitting from the large stokes shift, lead-free perovskites and perovskite variants can be used in the luminescent solar concentrators and X-ray scintillator. Thereby, new breakthroughs in theoretical predictions and preparation technology are still required in the area of lead-free light emitting perovskites and perovskite variants.

AUTHOR INFORMATION Corresponding Author *Email: [email protected] (G.N.). *Email: [email protected] (J.T.). ORCID Guangda Niu: 0000-0002-9285-4147 Jiang Tang: 0000-0003-2574-2943 30 ACS Paragon Plus Environment

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Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by the National Key R&D Program of China (2016YFB0700702), the National Natural Science Foundation of China (51761145048, 61725401, 51702107) and the Post-Doctoral Innovative Talent Support Program (BX20190127). ABBREVIATIONS QDs, quantum dots; LEDs, light emitting diodes; Pb, lead; LARP, Ligand Assisted Reprecipitation; PLQY, photoluminescence quantum yield; FE, free exciton; STE, self-trapped exciton; FWHM, full width at half maximum; YAG, Y3Al5O12:Ce3+; CIE, the commission international de L’Eclarage; CRI, color rendering index; CCT, correlated color temperature; PVDF, polyvinylidene fluoride. REFERENCES (1) MANDIL, C., Light's Labour's Lost: Policies For Energy-Efficient Lighting.

Energy world 2006, 343, 14-15. (2) Mueller-Mach, R.; Mueller, G. O.; Krames, M. R.; Trottier, T., High-Power Phosphor-Converted Light-Emitting Diodes based on III-Nitrides. IEEE J. Sel.

Top. Quant. 2002, 8 (2), 339-345. 31 ACS Paragon Plus Environment


Page 32 of 45

(3) Mueller-Mach, R.; Mueller, G.; Krames, M. R.; Höppe, H. A.; Stadler, F.; Schnick, W.; Juestel, T.; Schmidt, P., Highly Efficient All-Nitride PhosphorConverted White Light Emitting Diode. Phys. Status Solidi A 2005, 202 (9), 1727-1732. (4) Xia, Z.; Xu, Z.; Chen, M.; Liu, Q., Recent Developments in the New Inorganic Solid-State LED Phosphors. Dalton Transactions 2016, 45 (28), 11214-11232. (5) Chen, D.; Fang, G.; Chen, X., Silica-Coated Mn-Doped CsPb(Cl/Br)3 Inorganic Perovskite Quantum Dots: Exciton-to-Mn Energy Transfer and BlueExcitable Solid-State Lighting. ACS Appl. Mater. Interfaces 2017, 9 (46), 40477-40487. (6) Pust, P.; Weiler, V.; Hecht, C.; Tücks, A.; Wochnik, A. S.; Henß, A.-K.; Wiechert, D.; Scheu, C.; Schmidt, P. J.; Schnick, W., Narrow-Band RedEmitting Sr[LiAl3N4]:Eu2+ As A Next-Generation LED-Phosphor Material. Nat.

Mater. 2014, 13, 891. (7) Lin, C. C.; Liu, R.-S., Advances in Phosphors for Light-emitting Diodes. J.

Phys. Chem. Lett. 2011, 2 (11), 1268-1277. (8) Wang, Z.; Chen, B.; Rogach, A. L., Synthesis, Optical properties and Applications of Light-Emitting Copper Nanoclusters. Nanoscale Horiz. 2017, 2 (3), 135-146.


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


(9) Bolton, O.; Lee, K.; Kim, H.-J.; Lin, K. Y.; Kim, J., Activating Efficient Phosphorescence From Purely Organic Materials by Crystal Design. Nat.

Chem. 2011, 3, 205. (10)

Liu, Y.; Yao, D.; Zhang, H., Self-Assembly Driven Aggregation-

Induced Emission of Copper Nanoclusters: A Novel Technology for Lighting.

ACS Appl. Mater. Interfaces 2018, 10 (15), 12071-12080. (11)

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 (6), 3692-3696. (12)

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 (41), 9163-9168. (13)

Kim, Y.-H.; Cho, H.; Heo, J. H.; Kim, T.-S.; Myoung, N.; Lee, C.-L.; Im,

S. H.; Lee, T.-W., Multicolored Organic/Inorganic Hybrid Perovskite LightEmitting Diodes. Adv. Mater. 2015, 27 (7), 1248-1254. (14)

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 (44), 7162-7167.



(15)

Page 34 of 45

Wang, N.; Cheng, L.; Ge, R.; Zhang, S.; Miao, Y.; Zou, W.; Yi, C.;

Sun, Y.; Cao, Y.; Yang, R.; Wei, Y.; Guo, Q.; Ke, Y.; Yu, M.; Jin, Y.; Liu, Y.; Ding, Q.; Di, D.; Yang, L.; Xing, G.; Tian, H.; Jin, C.; Gao, F.; Friend, R. H.; Wang, J.; Huang, W., Perovskite Light-Emitting Diodes based on SolutionProcessed Self-Organized Multiple Quantum Wells. Nat. Photonics 2016, 10, 699. (16)

Dohner, E. R.; Hoke, E. T.; Karunadasa, H. I., Self-Assembly of

Broadband White-Light Emitters. J. Am. Chem. Soc. 2014, 136 (5), 17181721. (17)

Dohner, E. R.; Jaffe, A.; Bradshaw, L. R.; Karunadasa, H. I., Intrinsic

White-Light Emission from Layered Hybrid Perovskites. J. Am. Chem. Soc. 2014, 136 (38), 13154-13157. (18)

Smith, M. D.; Connor, B. A.; Karunadasa, H. I., Tuning the

Luminescence of Layered Halide Perovskites. Chem. Rev. 2019, 119 (5), 3104-3139. (19)

Smith, M. D.; Karunadasa, H. I., White-Light Emission from Layered

Halide Perovskites. Acc. Chem. Res. 2018, 51 (3), 619-627. (20)

Smith, M. D.; Watson, B. L.; Dauskardt, R. H.; Karunadasa, H. I.,

Broadband Emission with a Massive Stokes Shift from Sulfonium Pb–Br Hybrids. Chem. Mater. 2017, 29 (17), 7083-7087. (21)

Mao, L.; Wu, Y.; Stoumpos, C. C.; Traore, B.; Katan, C.; Even, J.;

Wasielewski, M. R.; Kanatzidis, M. G., Tunable White-Light Emission in 34 ACS Paragon Plus Environment

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


Single-Cation-Templated Three-Layered 2D Perovskites (CH3CH2NH3)4Pb3Br10–xClx. J. Am. Chem. Soc. 2017, 139 (34), 11956-11963. (22)

Yuan, Z.; Zhou, C.; Tian, Y.; Shu, Y.; Messier, J.; Wang, J. C.; van de

Burgt, L. J.; Kountouriotis, K.; Xin, Y.; Holt, E.; Schanze, K.; Clark, R.; Siegrist, T.; Ma, B., One-Dimensional Organic Lead Halide Perovskites with Efficient Bluish White-Light Emission. Nat. Commun. 2017, 8, 14051. (23)

Mao, L.; Guo, P.; Kepenekian, M.; Hadar, I.; Katan, C.; Even, J.;

Schaller, R. D.; Stoumpos, C. C.; Kanatzidis, M. G., Structural Diversity in White-Light-Emitting Hybrid Lead Bromide Perovskites. J. Am. Chem. Soc. 2018, 140 (40), 13078-13088. (24)

Luo, J.; Li, S.; Wu, H.; Zhou, Y.; Li, Y.; Liu, J.; Li, J.; Li, K.; Yi, F.; Niu,

G.; Tang, J., Cs2AgInCl6 Double Perovskite Single Crystals: Parity Forbidden Transitions and Their Application For Sensitive and Fast UV Photodetectors.

ACS Photonics 2018, 5 (2), 398-405. (25)

Pan, W.; Wu, H.; Luo, J.; Deng, Z.; Ge, C.; Chen, C.; Jiang, X.; Yin,

W.-J.; Niu, G.; Zhu, L.; Yin, L.; Zhou, Y.; Xie, Q.; Ke, X.; Sui, M.; Tang, J., Cs2AgBiBr6 Single-Crystal X-ray Detectors with A Low Detection Limit. Nat.

Photonics 2017, 11 (11), 726-732. (26)

Giustino, F.; Snaith, H. J., Toward Lead-Free Perovskite Solar Cells.

ACS Energy Lett. 2016, 1 (6), 1233-1240. (27)

Leng, M.; Yang, Y.; Chen, Z.; Gao, W.; Zhang, J.; Niu, G.; Li, D.;

Song, H.; Zhang, J.; Jin, S.; Tang, J., Surface Passivation of Bismuth-Based 35 ACS Paragon Plus Environment


Page 36 of 45

Perovskite Variant Quantum Dots To Achieve Efficient Blue Emission. Nano

Lett. 2018, 18 (9), 6076-6083. (28)

Leng, M.; Yang, Y.; Zeng, K.; Chen, Z.; Tan, Z.; Li, S.; Li, J.; Xu, B.;

Li, D.; Hautzinger, M. P.; Fu, Y.; Zhai, T.; Xu, L.; Niu, G.; Jin, S.; Tang, J., AllInorganic Bismuth-Based Perovskite Quantum Dots with Bright Blue Photoluminescence and Excellent Stability. Adv. Funct. Mater. 2018, 28 (1), 1704446. (29)

Zhang, J.; Yang, Y.; Deng, H.; Farooq, U.; Yang, X.; Khan, J.; Tang,

J.; Song, H., High Quantum Yield Blue Emission from Lead-Free Inorganic Antimony Halide Perovskite Colloidal Quantum Dots. ACS Nano 2017, 11 (9), 9294-9302. (30)

Chen, M.-Y.; Lin, J.-T.; Hsu, C.-S.; Chang, C.-K.; Chiu, C.-W.; Chen,

H. M.; Chou, P.-T., Strongly Coupled Tin-Halide Perovskites to Modulate Light Emission: Tunable 550–640 nm Light Emission (FWHM 36–80 nm) with a Quantum Yield of up to 6.4%. Adv. Mater. 2018, 30 (20), 1706592. (31)

Zhang, X.; Wang, C.; Zhang, Y.; Zhang, X.; Wang, S.; Lu, M.; Cui, H.;

Kershaw, S. V.; Yu, W. W.; Rogach, A. L., Bright Orange Electroluminescence from Lead-Free Two-Dimensional Perovskites. ACS Energy Lett. 2019, 4 (1), 242-248. (32)

Wang, A.; Guo, Y.; Zhou, Z.; Niu, X.; Wang, Y.; Muhammad, F.; Li, H.;

Zhang, T.; Wang, J.; Nie, S.; Deng, Z., Aqueous Acid-Based Synthesis of


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


Lead-Free Tin Halide Perovskites with Near-Unity Photoluminescence Quantum Efficiency. Chem. Sci. 2019, 10 (17), 4573-4579. (33)

Tan, Z.; Li, J.; Zhang, C.; Li, Z.; Hu, Q.; Xiao, Z.; Kamiya, T.; Hosono,

H.; Niu, G.; Lifshitz, E.; Cheng, Y.; Tang, J., Highly Efficient Blue-Emitting BiDoped Cs2SnCl6 Perovskite Variant: Photoluminescence Induced by Impurity Doping. Adv. Funct. Mater. 2018, 28 (29), 1801131. (34)

Li, J.; Tan, Z.; Hu, M.; Chen, C.; Luo, J.; Li, S.; Gao, L.; Xiao, Z.; Niu,

G.; Tang, J.; Antimony Doped Cs2SnCl6 with Bright and Stable Emission.

Front. Optoelectron. 2019, 2, 1-9. (35)

Luo, J.; Wang, X.; Li, S.; Liu, J.; Guo, Y.; Niu, G.; Yao, L.; Fu, Y.; Gao,

L.; Dong, Q.; Zhao, C.; Leng, M.; Ma, F.; Liang, W.; Wang, L.; Jin, S.; Han, J.; Zhang, L.; Etheridge, J.; Wang, J.; Yan, Y.; Sargent, E. H.; Tang, J., Efficient and Stable Emission of Warm-White Light from Lead-Free Halide Double Perovskites. Nature 2018, 563 (7732), 541-545. (36)

Han, P.; Zhang, X.; Mao, X.; Yang, B.; Yang, S.; Feng, Z.; Wei, D.;

Deng, W.; Pullerits, T.; Han, K., Size Effect of Lead-Free Halide Double Perovskite on Luminescence Property. Sci. China Chem. 2019, 3, 1-9. (37)

Jun, T.; Sim, K.; Iimura, S.; Sasase, M.; Kamioka, H.; Kim, J.;

Hosono, H., Lead-Free Highly Efficient Blue-Emitting Cs3Cu2I5 with 0D Electronic Structure. Adv. Mater. 2018, 30 (43), 1804547. (38)

Benin, B. M.; Dirin, D. N.; Morad, V.; Wörle, M.; Yakunin, S.; Rainò,

G.; Nazarenko, O.; Fischer, M.; Infante, I.; Kovalenko, M. V., Highly Emissive 37 ACS Paragon Plus Environment


Page 38 of 45

Self-Trapped Excitons in Fully Inorganic Zero-Dimensional Tin Halides.

Angew, Chem. 2018, 57 (35), 11329-11333. (39)

Zhou, L.; Liao, J.-F.; Huang, Z.-G.; Wei, J.-H.; Wang, X.-D.; Li, W.-G.;

Chen, H.-Y.; Kuang, D.-B.; Su, C.-Y., A Highly Red-Emissive Lead-Free Indium-Based Perovskite Single Crystal for Sensitive Water Detection.

Angew, Chem. 2019, 58 (16), 5277-5281. (40)

Yang, P.; Liu, G.; Liu, B.; Liu, X.; Lou, Y.; Chen, J.; Zhao, Y., All-

inorganic Cs2CuX4 (X = Cl, Br, and Br/I) Perovskite Quantum Dots with BlueGreen Luminescence. Chem. Commun. 2018, 54 (82), 11638-11641. (41)

Xie, J.-L.; Huang, Z.-Q.; Wang, B.; Chen, W.-J.; Lu, W.-X.; Liu, X.;

Song, J.-L., New Lead-Free Perovskite Rb7Bi3Cl16 Nanocrystals with Blue Luminescence and Excellent Moisture-Stability. Nanoscale 2019, 11 (14), 6719-6726. (42)

Zhou, C.; Lin, H.; Tian, Y.; Yuan, Z.; Clark, R.; Chen, B.; van de Burgt,

L. J.; Wang, J. C.; Zhou, Y.; Hanson, K.; Meisner, Q. J.; Neu, J.; Besara, T.; Siegrist, T.; Lambers, E.; Djurovich, P.; Ma, B., Luminescent ZeroDimensional Organic Metal Halide Hybrids with Near-Unity Quantum Efficiency. Chem. Sci. 2018, 9 (3), 586-593. (43)

Xu, L.-J.; Sun, C.-Z.; Xiao, H.; Wu, Y.; Chen, Z.-N., Green-Light-

Emitting Diodes based on Tetrabromide Manganese(II) Complex through Solution Process. Adv. Mater. 2017, 29 (10), 1605739.


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


(44)

Xiao, Z.; Meng, W.; Wang, J.; Mitzi, D. B.; Yan, Y., Searching for

Promising New Perovskite-Based Photovoltaic Absorbers: The Importance of Electronic Dimensionality. Mater. Horiz. 2017, 4 (2), 206-216. (45)

Wang, X.; Meng, W.; Liao, W.; Wang, J.; Xiong, R.-G.; Yan, Y.,

Atomistic Mechanism of Broadband Emission in Metal Halide Perovskites. J.

Phys. Chem. Lett. 2019, 10 (3), 501-506. (46)

Zhou, Y.; Zhou, Z.; Chen, M.; Zong, Y.; Huang, J.; Pang, S.; Padture,

N. P., Doping and Alloying for Improved Perovskite Solar Cells. J. Mater.

Chem. A 2016, 4 (45), 17623-17635. (47)

Abdi-Jalebi, M.; Andaji-Garmaroudi, Z.; Cacovich, S.; Stavrakas, C.;

Philippe, B.; Richter, J. M.; Alsari, M.; Booker, E. P.; Hutter, E. M.; Pearson, A. J.; Lilliu, S.; Savenije, T. J.; Rensmo, H.; Divitini, G.; Ducati, C.; Friend, R. H.; Stranks, S. D., Maximizing and Stabilizing Luminescence from Halide Perovskites with Potassium Passivation. Nature 2018, 555, 497. (48)

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 (12), 7376-7380. (49)

Zhou, D.; Liu, D.; Pan, G.; Chen, X.; Li, D.; Xu, W.; Bai, X.; Song, H.,

Cerium and Ytterbium Codoped Halide Perovskite Quantum Dots: A Novel and Efficient Downconverter for Improving the Performance of Silicon Solar Cells. Adv. Mater. 2017, 29 (42), 1704149.



(50)

Page 40 of 45

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 (7), 2138-2141. (51)

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 (27), 8453-8464. (52)

Filip, M. R.; Hillman, S.; Haghighirad, A. A.; Snaith, H. J.; Giustino, F.,

Band Gaps of the Lead-Free Halide Double Perovskites Cs2BiAgCl6 and Cs2BiAgBr6 from Theory and Experiment. J. Phys. Chem. Lett. 2016, 7 (13), 2579-2585. (53)

Volonakis, G.; Haghighirad, A. A.; Milot, R. L.; Sio, W. H.; Filip, M. R.;

Wenger, B.; Johnston, M. B.; Herz, L. M.; Snaith, H. J.; Giustino, F., Cs2InAgCl6: A New Lead-Free Halide Double Perovskite with Direct Band Gap. J. Phys. Chem. Lett. 2017, 8 (4), 772-778. (54)

Tran, T. T.; Panella, J. R.; Chamorro, J. R.; Morey, J. R.; McQueen, T.

M., Designing Indirect–Direct Bandgap Transitions In Double Perovskites.

Mater. Horiz. 2017, 4 (4), 688-693. (55)

Wei, F.; Deng, Z.; Sun, S.; Xie, F.; Kieslich, G.; Evans, D. M.;

Carpenter, M. A.; Bristowe, P. D.; Cheetham, A. K., The Synthesis, Structure and Electronic Properties of a Lead-Free Hybrid Inorganic–Organic Double


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


Perovskite (MA)2KBiCl6 (MA = methylammonium). Mater. Horiz. 2016, 3 (4), 328-332. (56)

Wei, F.; Deng, Z.; Sun, S.; Zhang, F.; Evans, D. M.; Kieslich, G.;

Tominaka, S.; Carpenter, M. A.; Zhang, J.; Bristowe, P. D.; Cheetham, A. K., Synthesis and Properties of a Lead-Free Hybrid Double Perovskite: (CH3NH3)2AgBiBr6. Chem. Mater. 2017, 29 (3), 1089-1094. (57)

Slavney, A. H.; Leppert, L.; Bartesaghi, D.; Gold-Parker, A.; Toney, M.

F.; Savenije, T. J.; Neaton, J. B.; Karunadasa, H. I., Defect-Induced BandEdge Reconstruction of a Bismuth-Halide Double Perovskite for Visible-Light Absorption. J. Am. Chem. Soc. 2017, 139 (14), 5015-5018. (58)

Filip, M. R.; Liu, X.; Miglio, A.; Hautier, G.; Giustino, F., Phase

Diagrams and Stability of Lead-Free Halide Double Perovskites Cs2BB'X6: B = Sb and Bi, B' = Cu, Ag, and Au, and X = Cl, Br, and I. J. Phys, Chem. C 2018,

122 (1), 158-170. (59)

Zhao, X.-G.; Yang, J.-H.; Fu, Y.; Yang, D.; Xu, Q.; Yu, L.; Wei, S.-H.;

Zhang, L., Design of Lead-Free Inorganic Halide Perovskites for Solar Cells via Cation-Transmutation. J. Am. Chem. Soc. 2017, 139 (7), 2630-2638. (60)

Xiao, Z.; Du, K.-Z.; Meng, W.; Mitzi, D. B.; Yan, Y., Chemical Origin of

the Stability Difference between Copper(I)- and Silver(I)-Based Halide Double Perovskites. Angewandte Chemie 2017, 129 (40), 12275-12279. (61)

Moser, F.; Lyu, S., Luminescence in Pure and I-doped AgBr Crystals.

J. Lumin. 1971, 3 (6), 447-458. 41 ACS Paragon Plus Environment


(62)

Page 42 of 45

Liu, Y.; Jing, Y.; Zhao, J.; Liu, Q.; Xia, Z., Design Optimization of

Lead-Free Perovskite Cs2AgInCl6:Bi Nanocrystals with 11.4% Photoluminescence Quantum Yield. Chem. Mater. 2019, 31 (9), 3333-3339. (63)

Locardi, F.; Cirignano, M.; Baranov, D.; Dang, Z.; Prato, M.; Drago, F.;

Ferretti, M.; Pinchetti, V.; Fanciulli, M.; Brovelli, S.; De Trizio, L.; Manna, L., Colloidal Synthesis of Double Perovskite Cs2AgInCl6 and Mn-Doped Cs2AgInCl6 Nanocrystals. J. Am. Chem. Soc. 2018, 140 (40), 12989-12995. (64)

Lee, W.; Hong, S.; Kim, S., Colloidal Synthesis of Lead-Free Silver–

Indium Double-Perovskite Cs2AgInCl6 Nanocrystals and Their Doping with Lanthanide Ions. J. Phys, Chem. C 2019, 123 (4), 2665-2672. (65)

Yang, B.; Mao, X.; Hong, F.; Meng, W.; Tang, Y.; Xia, X.; Yang, S.;

Deng, W.; Han, K., Lead-Free Direct Band Gap Double-Perovskite Nanocrystals with Bright Dual-Color Emission. J. Am. Chem. Soc. 2018, 140 (49), 17001-17006. (66)

Zhou, J.; Luo, J.; Rong, X.; Wei, P.; Molokeev, M. S.; Huang, Y.;

Zhao, J.; Liu, Q.; Zhang, X.; Tang, J.; Xia, Z., Lead-Free Perovskite variant Cs2SnCl6−xBrx Single Crystals for Narrowband Photodetectors. Adv, Optical

Mater. 2019, 7, 1900139. (67)

Breternitz, J.; Schorr, S., What Defines a Perovskite? Adv. Energy

Mater. 2018, 8 (34), 1802366. (68)

McCall, K. M.; Stoumpos, C. C.; Kostina, S. S.; Kanatzidis, M. G.;

Wessels, B. W., Strong Electron–Phonon Coupling and Self-Trapped Excitons 42 ACS Paragon Plus Environment

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


in the Defect Halide Perovskites A3M2I9 (A = Cs, Rb; M = Bi, Sb). Chem.

Mater. 2017, 29 (9), 4129-4145. (69)

Leng, M.; Chen, Z.; Yang, Y.; Li, Z.; Zeng, K.; Li, K.; Niu, G.; He, Y.;

Zhou, Q.; Tang, J., Lead-Free, Blue Emitting Bismuth Halide Perovskite Quantum Dots. Angew, Chem. 2016, 55 (48), 15012-15016. (70)

Yang, B.; Chen, J.; Hong, F.; Mao, X.; Zheng, K.; Yang, S.; Li, Y.;

Pullerits, T.; Deng, W.; Han, K., Lead-Free, Air-Stable All-Inorganic Cesium Bismuth Halide Perovskite Nanocrystals. Angew, Chem. 2017, 56 (41), 12471-12475. (71)

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. 2017, 56 (45), 1418714191. (72)

Bass, K. K.; Estergreen, L.; Savory, C. N.; Buckeridge, J.; Scanlon, D.

O.; Djurovich, P. I.; Bradforth, S. E.; Thompson, M. E.; Melot, B. C., Vibronic Structure in Room Temperature Photoluminescence of the Halide Perovskite Cs3Bi2Br9. Inorg. Chem. 2017, 56 (1), 42-45. (73)

Pal, J.; Bhunia, A.; Chakraborty, S.; Manna, S.; Das, S.; Dewan, A.;

Datta, S.; Nag, A., Synthesis and Optical Properties of Colloidal M3Bi2I9 (M = Cs, Rb) Perovskite Nanocrystals. J. Phys, Chem. C 2018, 122 (19), 1064310649.



(74)

Page 44 of 45

Roccanova, R.; Yangui, A.; Nhalil, H.; Shi, H.; Du, M.-H.; Saparov, B.,

Near-Unity Photoluminescence Quantum Yield in Blue-Emitting Cs3Cu2Br5-xIx (0 ≤ x ≤ 5). ACS Appl. Electronic Mater. 2019, 1 (3), 269-274. (75)

Li, T.; Mo, X.; Peng, C.; Lu, Q.; Qi, C.; Tao, X.; Ouyang, Y.; Zhou, Y.,

Distinct Green Electroluminescence from Lead-Free CsCuBr2 Halide MicroCrosses. Chem. Commun. 2019, 55 (31), 4554-4557. (76)

Shionoya, S.; Yen, W. M.; Yamamoto, H., Phosphor handbook. CRC

press: 2018. (77)

Ye, S.; Xiao, F.; Pan, Y. X.; Ma, Y. Y.; Zhang, Q. Y., Phosphors in

Phosphor-Converted White Light-Emitting Diodes: Recent Advances in Materials, Techniques and Properties. Mat. Sci. Eng. R 2010, 71 (1), 1-34.


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Lead-free halide perovskites and perovskite variants as phosphors toward light-emitting applications Jiajun Luo,† Manchen Hu,† Guangda Niu, *,† and Jiang Tang*,† †Sargent

joint research center, Wuhan National Laboratory for Optoelectronics

(WNLO) and School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, 430074, China

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Lead-Free Halide Perovskites and Perovskite Variants as Phosphors

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