Key Takeaways & Executive Findings
- •• • Bi doping increases the radiative recombination coefficient by one order of magnitude to 1.27×10−12 cm3/s, compared to intrinsic AgInS2 (9.63×10−13 cm3/s), directly enabling higher luminescence efficiency in light-emitting devices. • • Sb doping reduces the radiative recombination coefficient by three orders of magnitude to 1.36×10−16 cm3/s and introduces deep-level states at 1.08 eV below the conduction band minimum, exacerbating nonradiative losses and rendering Sb-doped AgInS2 unsuitable for optoelectronic applications. • • Under S-rich, In-poor, and Ag-moderate conditions, the formation energy of InAg antisite defects increases, reducing their concentration and mitigating deep-level trapping centers that limit carrier lifetimes. • • BiIn defects remain neutral across the Fermi level range, demonstrating superior defect tolerance that suppresses deep-level states, whereas SbIn defects are electrically active and detrimental to radiative recombination.
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Abstract
AgInS2, a representative I–III–VI2 chalcogenide, has garnered significant attention due to its tunable electronic structure, nontoxic nature, and air stability. However, its practical application is hindered by severe nonradiative recombination losses induced by deep-level InAg antisite defects, which act as carrier trapping centers. While Sb and Bi doping have been shown to suppress defect states in CuInS2, their impact on AgInS2 remains unexplored. This study systematically investigates Sb and Bi doping in AgInS2 from the perspectives of electronic orbitals interactions and defect regulation. Under S-rich, In-poor, and Ag-moderate conditions, the formation energy of InAg defects increases, thereby reducing their concentration. SbIn and BiIn emerge as dominant dopant-induced defects, yet they exhibit distinct effects on carrier recombination. Sb doping introduces deep-level states at 1.08 eV below the conduction band minimum through strong Sb–S antibonding interactions, exacerbating nonradiative recombination losses while reducing the radiative recombination coefficient by three orders of magnitude to 1.36×10−16 cm3/s versus intrinsic AgInS2’s 9.63×10−13 cm3/s. In contrast, BiIn defects remain neutral across the Fermi level range, with Bi doping demonstrating superior defect tolerance that effectively suppresses deep-level states and promotes radiative recombination. This enhances the radiative recombination coefficient by one order of magnitude to 1.27×10−12 cm3/s. This study offers critical insights into lone-pair electron effects in Ag-based chalcogenides, contributing to the advancement of sustainable and high-efficiency optoelectronic materials.
1. Introduction
Ternary I–III–VI2 semiconductors and their alloys (I: Ag+, Cu+; III: Ga3+, In3+, Al3+; VI: S2−, Se2−, Te2−), derived from cation cross-substitution, have garnered widespread interest due to their diverse applications in solar cells, photocatalysis, bioimaging, and light-emitting diodes. Among these materials, CuInS2 and AgInS2 quantum dots (QDs) have emerged as promising eco-friendly alternatives to conventional Cd- and Pb-based compounds, owing to their direct bandgap in the visible region, nontoxic composition, and excellent optoelectronic properties. While both materials share similarities, CuInS2 and AgInS2 exhibit distinct application advantages driven by their inherent properties. CuInS2 is primarily employed in solar cells owing to its stronger light absorption capabilities. Conversely, AgInS2 demonstrates superior suitability for light-emitting applications due to its broader bandgap tunability and enhanced stability.
Metal ion doping is a widely adopted strategy for modulating the electronic and optical properties of semiconductors. In CuInS2 and AgInS2 QDs, both isovalent and heterovalent doping (e.g., Al3+, Ga3+, Bi3+, Zn2+) have been extensively explored to tune spectral features, narrow full-width at half maximum (FWHM), regulate defect levels, and enhance material stability, thereby broadening their utility in optoelectronic applications. The luminescence mechanism of these materials is primarily governed by donor-acceptor pair (DAP) recombination, where deep donor and acceptor levels contribute to radiative transitions. As a result, precise defect design and control are critical for enhancing luminescence efficiency and reducing FWHM. Doping or alloying can effectively modify defect energy levels near the conduction band minimum (CBM) and valence band maximum (VBM), improve defect tolerance, suppress deep-level defects, and mitigate nonradiative recombination losses.
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LIU Gaoyu, ZHOU Wenhan, ANG Yee Sin, ZHANG Shengli, ZENG Haibo (2025). Lone-pair Bi dopants surpass Sb in orbital-defect synergistic regulation for enhanced radiative recombination in AgInS2. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3488-3
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Frequently Asked Questions
What is the primary nonradiative recombination pathway in intrinsic AgInS2, and how does Bi doping mitigate it?
The primary nonradiative pathway is mediated by deep-level InAg antisite defects, which act as carrier trapping centers. Bi doping mitigates this by increasing the formation energy of InAg defects under S-rich, In-poor, and Ag-moderate conditions, thereby reducing their concentration. Additionally, BiIn defects remain neutral across the Fermi level range, suppressing deep-level states and promoting radiative recombination, as evidenced by the radiative recombination coefficient increasing to 1.27×10−12 cm3/s.
Why does Sb doping degrade the radiative recombination coefficient by three orders of magnitude compared to intrinsic AgInS2?
Sb doping introduces deep-level states at 1.08 eV below the conduction band minimum through strong Sb–S antibonding interactions. These deep levels act as efficient nonradiative recombination centers, reducing the radiative recombination coefficient to 1.36×10−16 cm3/s, which is three orders of magnitude lower than the intrinsic value of 9.63×10−13 cm3/s.
What are the specific growth conditions that favor the suppression of InAg antisite defects?
S-rich, In-poor, and Ag-moderate conditions increase the formation energy of InAg defects, thereby reducing their concentration. This is critical for minimizing deep-level trapping centers and enhancing radiative recombination efficiency.
How do the electronic structures of SbIn and BiIn defects differ in terms of charge states across the Fermi level?
SbIn defects are electrically active and introduce deep-level states, whereas BiIn defects remain neutral across the entire Fermi level range. This neutrality is key to Bi's superior defect tolerance, as it prevents the formation of deep-level states that would otherwise promote nonradiative recombination.
What are the implications of these findings for the industrial adoption of AgInS2-based optoelectronic devices?
Bi doping enhances the radiative recombination coefficient by one order of magnitude, making AgInS2 more suitable for light-emitting applications. In contrast, Sb doping is detrimental due to severe nonradiative losses. These results guide the selection of dopants for optimizing luminescence efficiency and reducing FWHM in eco-friendly QD-based devices.
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