Achieving a near-unity photoluminescence quantum yield and high stability of CsPbI₃ nanoplatelets by hydroiodic acid-assisted ligand treatment

Abstract

Perovskite nanoplatelets (NPLs) display excellent photoluminescence (PL) properties and unique shape features, including thickness-dependent bandgap luminescence. However, perovskite NPLs, especially those based on iodides, exhibit poor spectral and phase stability. Herein, we propose a facile strategy to achieve a near-unity PL quantum yield (QY) and high stability of CsPbI₃ NPLs by employing hydrogen iodate (HI) for in situ etching-assisted surface modification of the short-chain strongly bound ligand dodecylamine (DDDAm). It is found that HI can etch off the incomplete octahedron [PbI₆]⁴⁻ on the surface of CsPbI₃ NPLs. Simultaneously, the excessive use of I⁻ ions and the introduction of DDDAm ligands effectively passivate the surface defects of NPLs, significantly improving their radiation recombination rate. As a result, the as-prepared CsPbI₃ NPLs exhibit up to 95% PL QY, maintaining PL characteristics even after 87 days of exposure to the atmospheric environment. Conversely, untreated CsPbI₃ NPLs display poor phase stability and transform into non-PL features (δ-CsPbI₃) after 21 days. As a proof of concept, we fabricated perovskite LEDs (PeLEDs) using these treated CsPbI₃ NPLs as luminescent layers for calibration. These PeLEDs showcase bright electroluminescence at 600 nm, with a full width at half maximum of 22 nm and an external quantum efficiency of 2.98%. The effective synthesis strategy using HI-assisted ligand treatment presented here is expected to be extended to the synthesis of other perovskite NPLs, thereby accelerating the integration of perovskite NPLs in optoelectronic technology.

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1. Introduction

All-inorganic perovskites have emerged as excellent candidates for light emitting diodes (LEDs), photodetectors, solar cells, and lasers because of their adjustable emitting range, high photoluminescence quantum yields (PL QYs), and high color purity.^1–7 Among these, perovskite nanoplatelets (NPLs) with varying thicknesses exhibit distinctive properties in bandgap tuning and photophysics, serving as valuable complements to perovskite quantum dots (QDs) and other nanoscale perovskites.^8–10 The controlled thickness of perovskite NPLs allows them to effectively address issues associated with other tuning methods, such as phase separation in mixed halide methods or severe aggregation in ultra-small QDs.^11,12 Consequently, these unique optoelectronic properties position perovskite NPLs as highly anticipated emerging materials in the optoelectronic field.

Despite the considerable potential of perovskite NPLs, their development significantly lags behind that of perovskite QDs, primarily due to inadequate stability.^13–15 During sample storage or film preparation, perovskite NPLs may undergo face-to-face or side-by-side fusion, resulting in changes in the emission color and even phase transitions.^16,17 For instance, face-to-face fusion can transform NPLs into bulks, diminishing quantum confinement effects and causing a redshift in emission.^18–20 This undesirable redshift poses a challenge for preparing red and blue emitters based on pure iodide and pure bromide perovskite NPLs, as achieving the required emission wavelength necessitates a quantum confinement-induced blueshift.^21–23 In addition to changes in the emission color, phase transitions in iodide-based NPLs present another challenge.^24–26 α-CsPbI₃ is inherently unstable due to its cubic nature; Cs⁺ ions in CsPbI₃ are insufficient to stabilize the cubic framework of the [PbI₆]⁴⁻ octahedron, allowing for phase transitions through dynamic motion.^27–30 Specifically, due to the low thickness and small width of CsPbI₃ NPLs, the area of the two planes is minimal, resulting in almost no ligand encapsulation.^31–33 Consequently, these CsPbI₃ NPLs tend to form nanowires through side-by-side fusion, typically found in δ-CsPbI₃ non-perovskite regions.^34–37 Current efforts to suppress perovskite QD fusion primarily focus on surface chemical improvements, including passivation of halogen defects or connecting strong ligands.^38,39 However, the reported surface treatment methods of perovskite QDs still face significant challenges in achieving both high stability and high luminescence performance for perovskite NPLs due to their inherently large specific surface area.^40–42

In the present work, for the first time, we report a hydroiodic acid (HI)-assisted ligand treatment method to obtain a near-unity quantum yield and excellent stability of CsPbI₃ NPLs. The incorporation of HI and the strong partial L-type coordination of the dodecylamine (DDDAm) ligand into CsPbI₃ NPLs were systematically studied to assess their impact on stability and luminescence properties. The results reveal that the introduced HI effectively etches the incomplete octahedron [PbI₆]⁴⁻ on the surface of CsPbI₃ NPLs, leading to a shift of the emission peak from 635 nm to 600 nm, indicating a more pronounced quantum confinement effect. The surface defects of CsPbI₃ NPLs are efficiently passivated with excess I⁻ ions and the newly introduced DDDAm ligands, significantly improving the radiative recombination rate. The photoluminescence QY of CsPbI₃ NPLs optimized by HI and new short-chain ligands can reach up to 95%, and their PL properties can be maintained even after 87 days of exposure to the atmospheric environment. In contrast, untreated modified CsPbI₃ NPLs exhibit poor phase stability, transforming into the non-optical phase of δ-CsPbI₃ after 21 days. Additionally, we explored the potential application of these CsPbI₃ NPLs in perovskite LEDs (PeLEDs). Utilizing the spin-coating solution processing technology, we successfully prepared PeLEDs based on these treated NPLs, showcasing bright electroluminescence (EL) at 600 nm, with a full width at half maximum (FWHM) of 22 nm and an external quantum efficiency (EQE) of 2.98%. This HI-assisted ligand treatment method presents a feasible strategy for preparing highly stable and low-defect CsPbI₃ NPLs, and it is anticipated that this method can be extended to the synthesis of other perovskite NPLs, contributing to the accelerated application of perovskite NPLs in optoelectronic technology.

2. Results and discussion

The CsPbI₃ NPLs were synthesized using a dynamic control method by varying the synthesis temperature. As observed in previous studies,^43,44 the PL peak of CsPbI₃ NPLs gradually shifts towards the blue side as the reaction temperature decreases, attributed to the enhanced quantum confinement effect (Fig. S1, ESI†). Simultaneously, the PL QY of CsPbI₃ NPLs with a strong confinement effect decreases gradually with the blue shift of the emission peak (Fig. S2, ESI†). At a PL wavelength of 635 nm, the PL QY of CsPbI₃ NPLs is only 12%, primarily due to the limitations imposed by a larger specific surface area on small-sized NPLs, making them more susceptible to non-radiative transitions caused by surface defects. In an attempt to mitigate the impact of surface defects on PL QY, a widely-used strong local L-shaped ligand, DDDAm, was employed for synergistic coordination modification of the NPLs. Introduction of DDDAm increased the PL QY of CsPbI₃ NPLs from 12% to 51% (Fig. S3, ESI†). However, due to the larger specific surface area of CsPbI₃ NPLs compared to QDs, this classical ligand modification method in QD systems has not been able to achieve the ideal near-unity PL QY for CsPbI₃ NPLs.

To address surface defects caused by the high specific surface area, we propose a strategy that combines acid etching and ligand exchange to prepare high-quality CsPbI₃ NPLs. As illustrated in Fig. 1a, HI was introduced into the synthesis process of CsPbI₃ NPLs to etch the incomplete octahedral [PbI₆]⁴⁻ on the surface of the NPLs, creating a halogen-rich environment on its surface to passivate halogen defects. Fig. 1b and c demonstrate that the PL peak of CsPbI₃ NPLs shifted from 635 nm to 600 nm after etching, and the corresponding PL QY increased from 12% to 47.8%. It is noteworthy that the amount of HI added significantly modulates the PL performance of CsPbI₃ NPLs (Fig. S4 and 5, ESI†). This is because the addition of HI not only etches the incomplete octahedral [PbI₆]⁴⁻ on the surface of CsPbI₃ NPLs, but also removes the weakly bound long-chain ligands oleic acid (OA) and oleamine (OAm), exposing more vacancy defects. After introducing the short-branched strong L-shaped ligand, DDDAm replaced the easily detachable OA/OAm and further passivated the surface defects of NPLs. As depicted in Fig. 1d, the PL peak of the treated CsPbI₃ NPLs remains at 600 nm, and the highest PL QY can reach 95% with good repeatability (Fig. S6, ESI†). The absorption spectra showed that the etched NPLs and treated NPLs possessed higher valley/peak ratios compared to the pristine NPLs, implying high size uniformity.⁴⁵ This observation is also verified from the FWHM of the PL spectra, which changed from 42 nm for the pristine NPLs to 23 nm and 22 nm etched and treated counterparts, respectively. This indicates that the surface modification strategy of DDDAm assisted by HI in situ etching can achieve CsPbI₃ NPLs with a high PL QY.

Fig. 1 HI-assisted ligand treatment method for the synthesis of CsPbI₃ NPLs. (a) Schematic outlines the synthesis strategy. (b–d) Absorption and PL spectra of (b) pristine CsPbI₃ NPLs, (c) etched CsPbI₃ NPLs using HI, and (c) treated CsPbI₃ NPLs using HI and the DDDAm ligand. The insets display digital photos of colloidal solutions on these NPLs under 365 nm UV lamp excitation.

To examine the impact of in situ etching with HI and surface modification with short-chain DDDAm ligands on the morphology of CsPbI₃ NPLs, we conducted characterization using transmission electron microscopy (TEM) technology on the pristine, etched, and treated NPLs. The TEM image reveals that pristine CsPbI₃ exhibits a hexagonal NPL morphology (Fig. 2a), with an average size of 23.78 nm. Upon the introduction of HI, the pristine CsPbI₃ NPLs underwent a regular arrangement, and the NPLs’ width was observed as 2 nm (Fig. 2b), indicating that the prepared NPLs consisted of 3 monolayers,⁴⁶ consistent with their absorption and PL characteristics. Notably, this regular arrangement of NPLs typically occurs in high-quality NPLs, possibly due to the self-assembly induced by HI etching of incomplete octahedra on the surface of CsPbI₃.⁴¹ Following the addition of DDDAm, there was no significant change in the morphology of the treated NPLs (Fig. 2c), aligning with the observation that the PL spectrum remained unchanged after adding DDDAm. High-resolution TEM images (Fig. 2d–f) indicate that the lattice spacing of the three types of NPLs is 0.32 nm, consistent with the lattice spacing of the (002) crystal plane of the α-CsPbI₃ phase,⁴⁷ suggesting that the crystal structure of the NPLs remained unaltered during etching and ligand treatment. These results imply that the crystal structure and morphology of the NPLs were preserved throughout the synthesis process with HI-assisted ligand treatment, contributing to the production of CsPbI₃ NPLs with good PL properties.

Fig. 2 Morphology of CsPbI₃ NPLs during the HI-assisted ligand treatment process. TEM images of (a) pristine, (b) etched, and (c) treated NPLs. High-resolution TEM images of (d) pristine, (e) etched, and (f) treated NPLs.

Fig. 3a displays the X-ray diffraction (XRD) pattern of the pristine, etched, and treated CsPbI₃ NPLs. The pristine CsPbI₃ NPLs exhibit distinct diffraction features consistent with known α-CsPbI₃.^20,47 In contrast, both etched and treated NPLs show XRD diffraction peaks with apparent periodicity (Fig. S7 and Table S1, ESI†). Calculation using Bragg's equation reveals a corresponding interlayer spacing of 5.1 nm for these NPLs, consistent with the sum of the thickness of CsPbI₃ NPLs and the size of surface ligands (OA/OAm) as shown in TEM observation. Such periodic diffraction is typically reported in high-quality NPLs,⁴⁸ suggesting self-assembly induced by HI etching of incomplete octahedra on the NPLs’ surface. This implies that CsPbI₃ NPLs synthesized through HI-assisted ligand treatment exhibit excellent crystallinity.

Fig. 3 The microstructure of the pristine, etched, and treated CsPbI₃ NPLs. (a) XRD patterns. (b) FTIR spectra. (c) N 1s, (d) Cs 3d, (e) Pb 4f, and (f) I 3d of XPS spectra.

To investigate the impact of in situ HI etching and short-chain DDDAm ligand modification on the surface states of CsPbI₃ NPLs, Fourier-transform infrared (FTIR) spectroscopy was conducted on these CsPbI₃ NPLs (Fig. 3b). For pristine NPLs, two stretching peaks at 1820 and 1570 cm⁻¹, attributed to C=O and –COO⁻ vibrations, are observed.⁴⁹ Additionally, a signal from the N–H bending vibration of amine functional groups is noted at 1624 cm⁻¹, indicating the presence of abundant OA and OAm ligands on the pristine NPLs’ surface.^49,50 In etched NPLs, the absorption peaks related to hydrocarbon groups (2798–3045 cm⁻¹ and 1454 cm⁻¹) and OA/OAm are significantly reduced, suggesting the removal of organic ligands after HI etching. For the treated NPLs, it exhibits a prominent N–H signal,⁴⁹ indicating effective coordination of DDDAm with the NPLs’ surface and efficient passivation of surface defects.

To further investigate the influence of HI in situ etching and DDDAm ligand modification on the surface atomic coordination environment of CsPbI₃ NPLs, X-ray photoelectron spectroscopy (XPS) characterization was conducted on these NPLs (Fig. 3c). For pristine NPLs, only one N peak is detected at 401.7 eV, confirming the presence of protonated amine −NH₃⁺,⁴⁹ likely originating from proton exchange between OAm and OA. After the addition of HI, the intensity of the –NH₃⁺ signal significantly decreases,⁴⁹ and another signal peak appears at 401.1 eV, indicating the removal of OA and the formation of a non-protonated amine (NH₂). The treated NPLs with surface ligand modification show a substantial enhancement of the NH₂ signal at 401.1 eV,^51,52 associated with the non-protonated amine of DDDAm. The binding energy of Cs 3d shows no significant changes after HI in situ etching and DDDAm treatment (Fig. 3d). Upon the addition of HI, the binding energies of Pb 4f shift from the initial 142.05 eV and 137.2 eV (pristine CsPbI₃) to 142.3 eV and 137.45 eV (etched CsPbI₃), and I 3d binding energies change from the original 629.3 eV and 617.8 eV (pristine NPLs) to 629.7 eV and 618.2 eV (etched NPLs). This is attributed to the enhancement of chemical bonds between Pb²⁺ and I⁻ in the surface octahedron [PbI₆]⁴⁻ due to the introduction of HI and excess I⁻ ions. Following the addition of DDDAm, the Pb 4f binding energy increases by 0.1 eV, and the I 3d binding energy increases by 0.3 eV,⁵³ indicating the strengthening of the interaction between DDDAm and I⁻ ions, influencing the chemical environment around them.^41,49 These results further confirm that HI in situ etching removed the octahedral [PbI₆]⁴⁻ and assisted in bridging strong L-shaped coordination with DDDAm on the surface of NPLs, effectively passivating the surface defects of the CsPbI₃ NPLs and enhancing their optical properties.

It is reported that CsPbI₃ NPLs typically exhibit a significant tail emission due to strong quantum confinement effects, believed to be caused by many defects.^54,55 In our study, after in situ etching with HI and ligand treatment, the wavelength blue shift and asymmetry in the long-wavelength region of CsPbI₃ NPLs were effectively suppressed, indicating a reduction in iodine vacancy defects. To further clarify this point, the Urbach energy (E_U) of these NPLs was calculated by plotting the absorption coefficient as a function of photon energy. Generally, the defect density of semiconductors is positively correlated with E_U, meaning that samples with more defects exhibit a larger E_U.⁵⁶ The E_U values of the pristine, etched, and treated NPLs are shown in Fig. 4a based on the fitting curve of the absorption spectra. The calculation results show that the E_U value of pristine NPLs is 43.48 meV. After the introduction of HI, the E_U value of the etched NPLs decreased to 19.23 meV, indicating that HI etched the incomplete octahedra on the surface of CsPbI₃, and iodine ions reduced the iodine vacancy defects in the NPLs. The treated NPLs with DDDAm ligands showed a decrease in E_U value from 19.23 meV to 15.87 meV, indicating that the addition of DDDAm further passivated the surface defects of CsPbI₃ NPLs and reduced their defect density. These results confirm that in situ HI etching and DDDAm ligand modification strategies can effectively slow down the defect states on the surface of CsPbI₃ NPLs and improve their optical properties.

Fig. 4 The photophysical properties of CsPbI₃ NPLs. (a) Urbach energy spectra and (b) PL decay curves of the pristine, etched, and treated NPLs. (c and d) The function and fitting curve of the reciprocal of the PL intensity and temperature for both the pristine and treated NPLs. (e and f) Schematic representations of the PL radiative recombination process for the pristine and treated NPLs.

To understand the impact of in situ etching with HI and ligand passivation on the radiative recombination of CsPbI₃ NPLs, we obtained the PL decay curves of these NPLs as shown in Fig. 4b. The fitted results (Table S2, ESI†) illustrate that the average lifetime (τ_avg) decreased from 22.22 ns in the pristine NPLs to 14.08 ns in the etched NPLs after the addition of HI etching.⁴⁶ This decrease is attributed to the introduction of defects caused by HI etching of incomplete octahedra on the CsPbI₃ surface and the removal of the ligand OA/OAm on the etched NPL surface. Following the introduction of DDDAm, the average lifetime of the treated NPLs increased to 17.08 ns, indicating that DDDAm further passivated defects on the NPL surface.⁴³ By measuring PL QY and average lifetime data, we calculated the non-radiative rate (k_nr) using the formula:⁴³

The calculated results shown in Table S2 (ESI)† revealed that, compared to the untreated pristine NPLs, the k_nr of the etched NPLs was significantly reduced, suggesting that in situ HI etching and DDDAm ligand modification strategies effectively inhibit the non-radiative recombination process of CsPbI₃ NPLs.

Temperature-dependent PL spectroscopy (Fig. S8, ESI†) was also conducted on both the pristine and treated NPL samples to gain insight into HI-assisted ligand treatment on the PL recombination of the NPLs. Fig. 4c and d depict the relationship between the integrated strength and temperature of the NPLs, which can be fitted using the following formula:⁵⁶

Here, I(T) is the PL strength at different temperatures, I₀ is the strength at 0 K, E_b is the exciton binding energy, and k_B is the Boltzmann constant. The results indicated that the exciton binding energy of the treated NPLs was 123 meV, significantly higher than that of the pristine NPLs at 33 meV. This finding further substantiates that in situ etching and ligand passivation can reduce iodine vacancy defects in CsPbI₃ NPLs, diminish shallow electron traps, and address the under-coordination of surface Pb atoms. The corresponding PL recombination process in the treated NPLs before and after treatment is shown in Fig. 4e and f. It is found that the introduction of HI in situ etching and DDDAm ligand modification results in the removal of most surface defects originating from iodine vacancies by HI. Simultaneously, HI introduced excessive iodine ions and DDDAm ligands to fill these trap states, leading to a reduction in non-radiative recombination and a significant increase in radiative recombination. This enhancement in radiative recombination ultimately contributes to the improved PL QY of CsPbI₃ NPLs.

Next, we tested the stability of CsPbI₃ NPLs through our HI-assisted ligand treatment. These NPLs were placed in n-hexane solution under ambient conditions (temperature 27 ± 5 °C, humidity 70 ± 20%) for 21 days to assess changes in their PL properties and crystal structure. Fig. 5a shows digital photos of pristine and treated NPLs before and after 21 days. It can be observed that the solution of pristine CsPbI₃ NPLs changed from red to yellow with partial precipitation, while the treated CsPbI₃ NPLs showed no significant color change. The corresponding PL tests indicated that the treated CsPbI₃ NPLs maintained 91% PL QY after 21 days, whereas the pristine CsPbI₃ NPLs lost their luminescence properties as shown in Fig. 5b. Specifically, the treated CsPbI₃ NPLs maintained a PL QY of 61.8% even after 87 days under ambient conditions (see Fig. S9, ESI†), exhibiting outstanding stability, as shown in Table S3 (ESI).† It can be observed that the XRD patterns (Fig. 5c and d) of the treated CsPbI₃ NPLs showed no significant change after 21 days, while the XRD pattern of the pristine CsPbI₃ NPLs involved from the α-phase to the yellow δ-phase,⁵⁷ confirming the transformation of its solution from the luminescent perovskite phase to the non-luminescent yellow phase. We tested the stability of both the pristine and treated NPL films after one week of ambient storage (Fig. S10, ESI†). The film with pristine NPLs exhibited a continuous red-shift in the PL peak position, along with a gradual decrease in PL intensity. In contrast, the treated NPL film maintained a stable PL peak position with no significant shift, and the PL intensity remained at 61.4% of the original level. This suggests enhanced stability in the treated NPL films compared to those with the pristine NPLs. We also monitored the PL evolution process of both types of NPLs at different power levels (Fig. 5e, f and Fig. S11, ESI†). Notably, the emission center of the pristine CsPbI₃ NPLs continuously shifted towards longer wavelengths even at the lowest power of 100 mW cm⁻², while the emission peak of the treated CsPbI₃ NPLs did not show a significant shift, even at the highest power of 500 mW cm⁻². The excellent spectral stability of the treated CsPbI₃ NPLs is attributed to the strong coordination of DDDAm on the NPL surface assisted by HI, inhibiting fusion between NPLs. This suggests that the in situ HI etching and DDDAm ligand modification strategy effectively enhances the stability of CsPbI₃ NPLs.

Fig. 5 The stability of CsPbI₃ NPLs. (a) Digital photos of the pristine and treated NPLs before and after 21 days of exposure to environmental conditions, and (b) the corresponding PL QY variation curves. (c and d) XRD patterns of the pristine (c) and treated (d) NPLs before and after 21 days of exposure to environmental conditions. (e and f) 2D pseudo color PL spectral evolution of the pristine (e) and treated (f) NPLs under continuous 365 nm UV light irradiation for 1 h.

To evaluate the potential application of CsPbI₃ NPLs prepared through in situ etching with HI and passivation using DDDAm ligands in optoelectronic devices, we fabricated a PeLED utilizing the treated CsPbI₃ NPLs as the emission layer. The device structure is composed of ITO/PEDOT:PSS/Poly TPD/CsPbI₃/TPBi/LiF/Al, as depicted in Fig. 6a. This PeLED exhibits bright EL with an emission center at 600 nm and a FWHM of 23 nm, along with CIE coordinates of (0.60, 0.35) (Fig. S12, ESI†). Notably, as the operational voltage of the PeLED increases, there is no significant shift in the EL peak position (Fig. 6b). This suggests that the strategies involving HI in situ etching and DDDAm ligand modification substantially enhance the stability of the CsPbI₃ NPLs. In Fig. 6c, it is demonstrated that the PeLED achieves a maximum brightness of 472.85 cd m⁻² at a current density of 31.2 mA cm⁻², accompanied by a peak EQE of 2.98% (Fig. 6d) and a luminous efficiency of 7.18 cd A⁻¹ (Fig. S14, ESI†). Even when the brightness exceeds 100 cd m⁻², the EQE remains at 2.36% (Fig. S13, ESI†). This performance is comparable to that of NPL-based PeLEDs reported in the literature (Table S4, ESI†), suggesting promising application prospects for CsPbI₃ NPLs prepared through HI in situ etching and DDDAm ligand modification strategies in optoelectronic devices.

Fig. 6 EL performance of PeLEDs based on the treated CsPbI₃ NPLs. (a) Structure and (b) EL spectra of PeLEDs under different voltage drivings. (c) Current density–brightness–voltage relationship, and (d) EQE–brightness relationship of PeLEDs.

3. Conclusion

In conclusion, we have demonstrated a HI-assisted ligand treatment strategy for the preparation of near-unity QY and highly stable CsPbI₃ NPLs. Our study reveals that HI can etch away incomplete octahedral facets on the surface of the NPLs, while the introduced short-chain DDDAm ligands effectively passivate surface defects and enhance the stability. The CsPbI₃ NPLs prepared through this strategy exhibit a high PL QY of 95%, and even after 21 days of exposure to environmental conditions, the PL QY remains at 91%, maintaining a remarkable 61.8% after 87 days. The PeLED device based on CsPbI₃ NPLs achieves a peak EQE of 2.98%, maintaining an EQE of 2.36% at a high brightness of 100 cd m⁻², showing excellent EL performance. This efficient synthesis strategy, utilizing HI-assisted ligand treatment, is expected to be applicable to the synthesis of other perovskite NPLs, facilitating the broader integration of perovskite NPLs in optoelectronic technology.

Author contributions

S. C., B. Z., and J. Z. supervised this work. S. C. and Z. L. conceptualized and designed the experiments. Z. L., K. X., and Z. D. carried out the main experimental work, including materials synthesis, optical characterizations, data analysis. Y. S. conducted the fabrication of PeLEDs and the related performance tests. S. C., Z. L., and Y. S. co-wrote the manuscript. All authors were involved in the results discussion and manuscript preparation.

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgements

This work was supported by the Outstanding Youth Fund of the Guangxi Natural Science Foundation (2022GXNSFFA035032), the National Natural Science Foundation of China (62165001, 12174075), the special fund for “Guangxi Bagui Scholars”, and the “Guangxi Hundred-Talent Program”. The Center for Instrumental Analysis of Guangxi University is acknowledged for providing research facilities and resources for the experiments.

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Footnotes

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4qi00168k

‡ Both authors contributed equally to this work.

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