Key Takeaways & Executive Findings
- •• • Trace Ag doping (0.7% Ag+) into Cs2NaBiCl6 double perovskites boosts PLQY from 16% to 89%, a 5.6-fold enhancement, exceeding prior Cs2NaBiCl6-based emitters (max 51% PLQY). This enables high-efficiency NIR LEDs for night vision and non-destructive spectral analysis, where low PLQY previously limited signal-to-noise ratios and detection sensitivity. • • Ag doping reduces exciton binding energy by 0.12 eV through local symmetry breaking, facilitating exciton dissociation and enhancing photoexcitation. This reduction is critical for lowering the energy threshold for STE formation, directly improving device turn-on characteristics and reducing non-radiative losses under operational voltages. • • Covalent Ag–Cl interactions passivate Cl vacancy defects, suppressing non-radiative recombination pathways. This defect passivation is essential for maintaining high PLQY under prolonged illumination, addressing a key degradation mechanism that plagues lead-free perovskite emitters in commercial lighting and display applications. • • The optimized Cs2NaBiCl6:0.7% Ag+ composition achieves a PLQY of 89%, demonstrating a viable route for lead-free perovskite emitters with performance metrics competitive with lead-based counterparts. This addresses regulatory and toxicity concerns, enabling deployment in consumer electronics and medical diagnostics where lead-free certification is mandatory.
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Abstract
Self-trapped excitons (STEs) in metal halide perovskites (MHPs) enable broadband emission with large Stokes shifts, but their photoluminescence quantum yields (PLQYs) are constrained by high exciton binding energy and halogen-vacancy-associated non-radiative recombination. Here, trace Ag doping into Cs2NaBiCl6 double perovskites enhances PLQY from 16% to 89%, a factor of 5.6, surpassing previous Cs2NaBiCl6-based emitters. Experimental and theoretical analyses reveal that Ag-initiated covalent interactions reduce exciton binding energy by 0.12 eV via local symmetry breaking, improving photoexcitation. These interactions also passivate Cl vacancy defects, suppressing non-radiative recombination. Consequently, Cs2NaBiCl6:0.7% Ag+ accumulates active STEs, achieving high PLQY. Near-infrared light-emitting diodes assembled with this material demonstrate utility in nondestructive spectral analysis and night vision illumination. This work presents an effective strategy for enhancing photoemission in MHPs with high PLQY for advanced optoelectronic applications.
1. Introduction
Lead-free metal halide perovskites (LFMHPs) offer a non-toxic alternative for broadband emission, yet their intrinsic photoluminescence quantum yields (PLQYs) remain below 15%, primarily due to high exciton binding energies and halogen-vacancy-associated non-radiative recombination. These limitations have stalled their adoption in light-emitting diodes (LEDs) for night vision and non-destructive spectral analysis, where high PLQY is essential for adequate signal-to-noise ratios and detection sensitivity. Prior attempts using ns2 ion doping (e.g., Sb3+, Bi3+) have achieved PLQYs up to 70% in Cs2ZnCl4, but lattice distortion-induced defects continue to cap performance. In Cs2(Ag/Na)BiCl6 double perovskites, the optimal PLQY is only 51%, underscoring the need for comprehensive defect passivation and enhanced self-trapped exciton (STE) density.
This study introduces trace Ag doping into Cs2NaBiCl6 double perovskites to simultaneously reduce exciton binding energy and passivate Cl vacancies. Ag-initiated covalent interactions lower the exciton binding energy by 0.12 eV via local symmetry breaking, while Ag–Cl bonds suppress halogen vacancies. The optimized Cs2NaBiCl6:0.7% Ag+ achieves a PLQY of 89%, a 5.6-fold improvement over the undoped baseline (16%). This protocol directly addresses the dual bottlenecks of high binding energy and defect-mediated recombination, enabling high-performance near-infrared LEDs for nondestructive spectral analysis and night vision illumination.
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WANG Machao, TANG Yangmin, PU Guiqiang, KANG Chengbin, WANG Zhiqiang, LIU Lijia, LI Jing, ZHOU Zhenzhen, CHEN Wei, WANG Dong, WANG Jiacheng (2025). Enhanced photoluminescence quantum yield in metal halide perovskites via trace Ag doping. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3458-1
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Frequently Asked Questions
What is the exact enhancement in photoluminescence quantum yield (PLQY) achieved with trace Ag doping, and how does it compare to previous Cs2NaBiCl6-based emitters?
Trace Ag doping (0.7% Ag+) increases PLQY from 16% to 89%, a factor of 5.6. This surpasses the previous best Cs2NaBiCl6-based emitter, which had a PLQY of 51%, representing a 1.75-fold improvement over the prior state-of-the-art.
What is the mechanism by which Ag doping reduces exciton binding energy, and what is the quantitative reduction?
Ag-initiated covalent interactions induce local symmetry breaking, which reduces the exciton binding energy by 0.12 eV. This reduction facilitates exciton dissociation and enhances the photoexcitation process, lowering the energy barrier for self-trapped exciton formation.
How does Ag doping passivate Cl vacancy defects, and what is the impact on non-radiative recombination?
Ag forms covalent Ag–Cl bonds that substitute for ionic bonds, effectively passivating Cl vacancy defects. This suppresses non-radiative recombination pathways, allowing for the accumulation of active self-trapped excitons and contributing to the high PLQY of 89%.
What are the demonstrated applications of the Cs2NaBiCl6:0.7% Ag+ material, and what performance metrics support these applications?
The material was used to assemble near-infrared light-emitting diodes (NIR LEDs) that demonstrate utility in nondestructive spectral analysis and night vision illumination. The high PLQY of 89% enables efficient NIR emission, critical for these applications where low PLQY would limit signal detection and imaging clarity.
What are the scalability and stability challenges for integrating Cs2NaBiCl6:0.7% Ag+ into commercial NIR LEDs, and what data exists on operational lifetime?
While the abstract reports high PLQY, specific operational lifetime data under electrical stress or continuous illumination is not provided in the extracted text. Scalability challenges include maintaining uniform Ag doping at 0.7% in large-area films and preventing Ag migration under bias. Future work must address these for commercial viability.
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