Highly Efficient Lead-Free (Bi,Ce)-Codoped Cs₂Ag_0.4Na_0.6InCl₆ Double Perovskites for White Light-Emitting Diodes

Abstract

Lead-free double perovskite phosphors are promising alternatives to lead halide perovskites for wide uses in optoelectronic applications, but suffer from a low quantum efficiency. Here, we propose to enhance the quantum efficiency of orange-emitting Cs 2 Ag 0.4 Na 0.6 InCl 6 :Bi via a codoping strategy. The internal quantum efficiency of Cs 2 Ag 0.4 Na 0.6 InCl 6 :1% Bi phosphor was increased from 89.9% to the record 98.4 and 98.6% by codoping with 1% Ni and 1% Ce, respectively. High-level density functional theory calculations have revealed that the enhanced efficiency is ascribed to the formation of shallow trap states by codoping with Ce, while codoping with Mn can create delocalized deep traps that decrease the quantum efficiency. By applying the (Bi,Ce)-codoped sample together with a blue BaMgAl 10 O 17 :Eu 2+ phosphor, a white light-emitting diode with an excellent color rendering index of 95.7 and a correlated color temperature of 4430 K has been demonstrated. The developed Cs 2 Ag 0.4 Na 0.6 InCl 6 :Bi,Ce phosphor shows a great potential as downconversion luminescent material in solid-state lighting for general illumination.

Highly Efficient and Tunable Emission of Lead‐Free Manganese Halides toward White Light‐Emitting Diode and X‐Ray Scintillation Applications

“…Thanks to the chemical and structural diversity of metal halide perovskite family, various luminescent lead-free metal halide perovskites (LFMHPs) or their variants have been synthesized and characterized based on metal ions such as Bi 3+ , Sb 3+ , In 3+ , Cu + , Sn 2+ , Mn 2+ with crystal dimensionality from 0D to 3D, and some with reduced dimensionality have revealed superior stability compared with their Pb-based counterparts. [28][29][30][31][32][33][34][35][36][37] Some lead-free perovskites or variants such as Bi, Ce-codoped Cs 2 Ag 0.6 Na 0.4 InCl 6 , [37] (C 4 N 2 H 14 Br) 4 SnBr 6 , [38] and (TEBA) 2 SbCl 5 [28] have exhibited high photoluminescence quantum yield (PLQY) of over 80% and been used as downconversion phosphors to achieve white light emission blended with corresponding commercial phosphors. In addition, some analogs with high PLQY and large stokes shifts such as (C 8 H 17 NH 3 ) 2 SnBr 4 , [39] Cs 2 Ag 0.6 Na 0.4 In 0.85 Bi 0.15 Cl 6 , [40] and Rb 2 CuBr 3 [41] have also been studied as X-ray scintillators showing high light yield under X-ray excitation.…”

Lead‐Free Halide Double Perovskite Nanocrystals for Light‐Emitting Applications: Strategies for Boosting Efficiency and Stability

“…found that the PLQY of Cs 2 Ag 0.4 Na 0.6 InCl 6 could be boosted from 89.9% to 98.6% and 98.4% via Bi 3+ ‐Ce 3+ and Bi 3+ ‐Ni 3+ co‐doped, respectively, which were the highest value in the reported HDP materials and exhibited a great potential in solid‐state lighting. [ 76 ]…”

“…In summary, the metal cation doping/alloying strategies are effective pathways for modulating photoelectric performance of lead‐free HDPs, which can realize the variable bandgap, adjustable electronic structure, enhanced PL intensity, and tunable emission peak and PL excitation peak. Although the HDP bulk materials prepared via metal cation doping are almost the same PLQY as lead halide perovskite nanocrystals, [ 6,67,76 ] the PL properties of lead‐free HDPs nanocrystals still are unsatisfactory for practical commercialization for future solid‐state lightings and displays. Hence, boosting PL properties of HDP nanocrystals by metal doping/alloying strategies still needs further study.…”

“…The device exhibited CIE color coordinates of (0.37, 0.35), and CRI of 81.9 and CCT of 4179 K. In addition, Gray and co‐workers [ 183 ] employed blue Cs 2 NaInCl 6 :Sb 3+ phosphors with emission at 452 nm and PLQY of 79%, together with green β ‐SiAlON:Eu 2+ phosphors and red Sr 2 Si 5 N 8 :Eu 2+ phosphors on 370 nm UV LED chip, which exhibited CIE color coordinates of (0.3890, 0.4009), CCT of 3972.6 K and CRI of 90.6, making Cs 2 NaInCl 6 :Sb 3+ phosphors as an alternative for commercial blue phosphors ( Figure a,b). Moreover, Wang and co‐workers [ 76 ] fabricated WLED devices by Bi 3+ ‐Ce 3+ co‐doped Cs 2 Ag 0.4 Na 0.6 InCl 6 phosphors with high PLQY as well as blue BaMgAl 10 O 17 :Eu 2+ phosphor. The mass ratio between blue BaMgAl 10 O 17 :Eu 2+ phosphor and Bi 3+ ‐Ce 3+ co‐doped Cs 2 Ag 0.4 Na 0.6 InCl 6 phosphors could tune CCT from 8362 to 2796 K (Figure 10c).…”

“…Lead‐free HDP nanocrystals have been documented wide application prospects in solar cells, [ 53–57 ] LEDs, [ 58 ] photocatalysis, [ 59,60 ] photodetectors, [ 61 ] and many other optoelectronic fields. [ 62,63 ] Although Sn 4+ ‐based, [ 64–67 ] Zr 4+ ‐based, [ 68 ] Na + /Bi 3+ ‐based, [ 69,70 ] Na + /In 3+ ‐based, [ 71 ] K + /In 3+ ‐based, [ 71 ] Ag + /In 3+ ‐based, [ 72–77 ] and Mn 2+ /Bi 3+ ‐based, [ 78,79 ] lead‐free HDP bulk materials with highly efficient emission ( Table 1 ) have been designed and synthesized in recent years, the photoluminescent (PL) properties of colloidal HDP nanocrystals still remain enormous challenge for application in LED devices compared with lead halide perovskite nanocrystals. The main reasons for poor PL performance of colloidal HDP nanocrystals can be ascribed to their intrinsic and surface defects, indirect band gaps, and forbidden transitions.…”