Lead‑Free Bismuth‑Doped Cs₂SnCl₆ and Mn‑Doped CsPbCl₃ Quantum Dots Deliver Highly Stable, High‑Efficiency White LEDs

Abstract

Perovskite quantum dots (QDs) are celebrated for their exceptional quantum yield, tunable bandgap, and ease of synthesis, making them ideal for white light‑emitting diodes (WLEDs). Yet, iodine‑containing red QDs suffer from photochemical instability. Here, we demonstrate a WLED that combines lead‑free bismuth‑doped Cs₂SnCl₆ (blue) and manganese‑doped CsPbCl₃ (orange) QDs. The device emits white light with chromaticity (0.334, 0.297), correlated color temperature 5311 K, and color rendering index (CRI) of 80. Both QD families exhibit excellent air‑stability, and the resulting WLED retains >90 % of its brightness after 300 h of continuous operation, setting a new benchmark for inorganic perovskite LEDs.

Introduction

White light‑emitting diodes (WLEDs) are the future of solid‑state lighting, offering superior energy efficiency, long lifetime, and high luminous efficacy. Quantum‑dot‑LEDs (QD‑LEDs) have emerged as a compelling platform due to their high photoluminescence quantum yield (PLQY) and spectral tunability. Perovskite QDs, in particular, achieve PLQYs above 90 % and can be synthesized at low temperature, but their widespread use is limited by the instability of iodine‑containing compositions and the toxicity of lead. Recent work has shown that doping perovskites with less toxic elements such as bismuth (Bi) or manganese (Mn) can preserve or even enhance optical performance while mitigating environmental concerns. This study introduces two lead‑free perovskite QDs—Bi‑doped Cs₂SnCl₆ and Mn‑doped CsPbCl₃—that emit blue and orange light, respectively. Both QDs share the same chloride anion, preventing anion‑exchange reactions during device assembly. The resulting WLED displays excellent color quality, high luminous efficiency, and record‑length operational stability.

Methods

Materials and Chemicals

High‑purity cesium carbonate, lead chloride, cesium chloride, oleic acid, 1‑octadecene, manganese chloride tetrahydrate, oleylamine, tin chloride, bismuth chloride, PMMA, hydrochloric acid, methanol, toluene, ethyl acetate, and hexane were sourced from Alfa Aesar, Aladdin, Macklin, Sinopharm, Kermel, Concord, and Beijing Chemical Factory, respectively.

Synthesis Processes

Preparation of Cs‑oleate

Cs‑oleate was prepared following Kovalenko’s protocol: 0.8 g Cs₂CO₃, 2.5 mL oleic acid, and 30 mL 1‑octadecene were heated under nitrogen to 150 °C until complete dissolution.

Mn‑Doped CsPbCl₃ QDs

Using a hot‑injection method, PbCl₂ (0.0615 g), MnCl₂·(H₂O)₄ (0.08 g), oleylamine, oleic acid, and ODE were combined and heated to 180 °C. After injecting dried ligands and 0.4 mL Cs‑oleate, the mixture was quenched in an ice bath. QDs were precipitated with hexane/ethyl acetate (1:3) and purified by centrifugation.

Bi‑Doped Cs₂SnCl₆

CsCl (0.337 g), SnCl₂ (0.189 g), BiCl₃ (0.032 g), and 4 mL 37 % HCl were sealed in a Teflon autoclave and heated at 220 °C for 20 h. The resulting white crystals were collected by centrifugation.

LED Fabrication

Commercial 365 nm UV chips were coated sequentially with a PMMA/toluene dispersion of Bi‑doped Cs₂SnCl₆ followed by Mn‑doped CsPbCl₃ QDs. After spin‑coating, the films were cured at room temperature for 30 min.

Characterization

Absorption spectra were recorded with a Shimadzu UV‑2550; fluorescence with an Ocean Optics spectrometer. PLQY was measured using an integrating sphere (FLS920P). Structural analysis employed TEM (FEI Tecnai G2), SEM/EDX (Quanta 450 FEG), and XRD (Bruker D8). Time‑resolved PL (TRPL) was performed on an Edinburgh FLS920. Electroluminescence (EL) and luminous efficacy were measured with an ATA‑1000 system.

Results and Discussion

Bi‑Doped Cs₂SnCl₆. Absorption peaked at ~375 nm, with a PL maximum at 465 nm (FWHM 65 nm) and a PLQY of 76 %. The material retained its PL intensity after 300 h of UV exposure and remained stable for three months in ambient air.

Mn‑Doped CsPbCl₃. The absorption edge at ~400 nm gave rise to dual PL peaks at 405 nm (host) and 595 nm (Mn²⁺ d‑d transition, FWHM ~80 nm). PLQY reached 52 %. The QDs preserved their photoluminescence for over three months under ambient conditions.

TRPL lifetimes were 375 ns for Bi‑doped Cs₂SnCl₆ and 1.7 ms for Mn‑doped CsPbCl₃, confirming the expected fast and slow emission channels, respectively.

SEM/TEM and EDX confirmed the crystalline phase and stoichiometry of both QDs. Optimal Mn doping (6.45 mg mL⁻¹) maximized PL intensity without affecting spectral width, maintaining stable chromaticity (0.535, 0.460).

WLED Performance. The assembled device exhibited two distinct EL peaks corresponding to the blue and orange emitters. At 15 mA, the color coordinates were (0.334, 0.297) with a CCT of 5311 K and CRI of 80. The luminous efficacy reached 20.8 lm W⁻¹ and luminance of 78 kcd m⁻². EL intensity scaled linearly with current up to 120 mA without spectral shift, indicating robust thermal stability.

Long‑term testing showed less than 10 % loss after 300 h of continuous operation, with a half‑life of 3000 h—significantly surpassing iodine‑based perovskite LEDs. At 15 mA, PL intensity remained at 99 % after 50 h and 97 % after 100 h.

Conclusion

By combining Bi‑doped Cs₂SnCl₆ (blue) and Mn‑doped CsPbCl₃ (orange) QDs, we have fabricated a lead‑free WLED that delivers high color quality (CRI 80), high luminous efficacy (20.8 lm W⁻¹), and exceptional operational stability (half‑life 3000 h). The shared chloride anion eliminates anion‑exchange degradation, while the lead‑free composition addresses environmental concerns. These findings pave the way for scalable, sustainable white‑light technologies based on inorganic perovskite quantum dots.

Abbreviations

QDs:

Quantum dots

WLEDs:

White light‑emitting diodes

QY:

Quantum yield

PL:

Photoluminescence

TRPL:

Time‑resolved photoluminescence spectroscopy

SEM:

Scanning electron microscope

EDX:

Energy dispersive X‑ray spectroscopy

XRD:

X‑ray diffraction

FWHM:

Full width at half maximum

EL:

Electroluminescence