Flexible polyphosphazene nanocomposite films: Enhancing stability and luminescence of CsPbBr3 perovskite nanocrystals

Husitu Lin Shuangkun Zhang Dianfa Zhao Yongkang Wang Wei Liu Fan Yang Jianjun Liu Dongpeng Yan Zhanpeng Wu

Citation:  Husitu Lin, Shuangkun Zhang, Dianfa Zhao, Yongkang Wang, Wei Liu, Fan Yang, Jianjun Liu, Dongpeng Yan, Zhanpeng Wu. Flexible polyphosphazene nanocomposite films: Enhancing stability and luminescence of CsPbBr3 perovskite nanocrystals[J]. Chinese Chemical Letters, 2025, 36(4): 109795. doi: 10.1016/j.cclet.2024.109795 shu

Flexible polyphosphazene nanocomposite films: Enhancing stability and luminescence of CsPbBr3 perovskite nanocrystals

English

  • The term “quantum dots (QD)” applicable in the semiconductor nanocrystals that features the size on the order of excitonic Bohr radius [1,2]. QDs [3,4] have gained much attention in the fields of solar cells, laser photon detectors, and light-emitting diodes (LEDs), by virtue of their excellent photoluminescence quantum yields (PLQY) and narrow emission bandgap. During the past several years, lead halide perovskite quantum dots (PQDs) with a general formula of ABX3 (where A = Cs, methylamine; B = Pb, Sn; X = Cl, Br, I) were extensively explored due to their tunable and efficient photoluminescence (PL) properties [59]. Unfortunately, these nanocrystals are highly unstable under environmental conditions, such as humidity, UV radiation, oxygen, heat, and polar solvent, which largely restrict their usage in long-term applications on industrial scale [10,11].

    A number of strategies have been employed to boost the stability of PQDs, including ion doping [12], surface passivation [13], coating [14], and the addition of organic polymers [1517]. Surface passivation is considered as a highly effective technique for achieving improved stability. Aggregation can be prevented effectively by introducing hydrophobic organic ligands, and defects on the surface of PQDs can be effectively passivated. In a recent study, Qiu et al. used a wide range of aromatic carboxylic acids as ligands for CsPbBr3 PQDs [18]. These PQDs displayed minimal reduction of photoluminescence intensity at ambient conditions and maintained their stability up to 100 h. Another strategy involves polymeric encapsulation of PQDs, by using polymethylmethacrylate (PMMA), polystyrene (PS) and ethylene vinyl acetate (EVA), which can improve their water resistance, mechanical performance and luminescent properties. Furthermore, to achieve stabilization of PQDs, polymer matrices must possess comprehensive properties, such as high transparency, excellent hydrophobicity, high thermal stability, and UV resistance.

    In comparison with traditional polymers with carbon backbones, polyphosphazenes are comprised of a versatile family of polymer built on —[P=N]— [19] backbones owing to high reactivity, which can be linked to a wide range of side chains [20,21]. This leads to the product with a similarly diverse range of physical and chemical properties. Polyphosphazenes have excellent thermal stability, high chain flexibility, high refractive index, flame retardant, biocompatible and optical transparency, which make them suitable to be applied in the fields of biomedical engineering, energy generation and storage, and aerospace materials [2226]. The nitrogen element [27] in backbone and the functional group at the side group exhibit coordination interactions with the metal nanoparticle and prevent their agglomeration. Poly(bis(phenoxy)phosphazene) (PBPP) [28] is a type of high-performance organic materials with excellent light stability, thermal stability, hydrophobicity and barrier properties. Simultaneously, poly(bis(4-esterphenoxyl)phosphazene) (PBEPP) [29] not only exhibits high light and chemical stability, but also can enhance the interface bonding strength between the metal ions and polyphosphazenes. Our group previous research has shown that some polyphosphazenes with aromatic side groups own higher fluorescence performance as well, which demonstrate the combination of CsPbBr3 PQDs and polyphosphazenes matrices may lead to a synergetic effect with enhanced luminescence. They both own conjugated structures that favor the charge transport, and the additional electron-withdrawing groups (like ester-phenoxyl) can also tailor the electronic structures and energy levels [30].

    In this work, we highlight the use of linear polyphosphazenes as both ligand and encapsulation material for PQDs. By utilizing coordinating groups like main-chain nitrogen and side-chain oxygen, the surface defects of CsPbBr3 can be passivated effectively. The PQDs were uniformly dispersed within the polymer matrix. As a result, CsPbBr3 QDs/PBPP and CsPbBr3 QDs/PBEPP flexible composite thin films were successfully fabricated (Scheme 1). These films demonstrated exceptional resistance abilities to a wide range of environments, such as water, UV light, high temperature and oxygen. Furthermore, the performance of two different phenoxy side group on PQDs was conducted. The high-performance composite thin films with remarkable transparence and flexibility in this study has strong applied potential in the field of luminescence and optoelectronics.

    Scheme 1

    Scheme 1.  Schematic illustration of preparation of CsPbBr3/polyphosphazene thin films.

    Fig. 1a shows the toluene solutions of CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP under sunlight, showing the uniform dispersion of PQDs in the polymer solution. These solutions remain clear and transparent, and exhibit significant fluorescence intensity under 365 nm UV light irradiation (Fig. 1d). The CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP films, which are prepared through the film casting method, display transparency after the solvent is evaporated at 75 ℃. When exposed to ultraviolet light, they emit bright green light (Figs. 1b and e). This result proved that there is no phase separation between CsPbBr3 PQDs and polyphosphazenes, and the structure of CsPbBr3 PQDs is not destroyed, during the heating and film formation processes, which can be further confirmed by the confocal fluorescence microscopy results (Fig. 2). The prepared polymer films also exhibit high flexibility and can be bent for many times (Figs. 1c, e and f), making them suitable for further processing and utilization.

    Figure 1

    Figure 1.  Photographs of (a, d) CsPbBr3 PQDs/PBPP-toluene and CsPbBr3 PQDs/PBEPP-toluene. (b, e) CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP thin films. (c, f) CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP thin films after bending. (a-c) Under daylight and (d-f) under UV (365 nm) light, respectively.

    Figure 2

    Figure 2.  Fluorescence images of (a) CsPbBr3 PQDs/PBPP and (b) CsPbBr3 PQDs/PBEPP thin film.

    The XRD patterns (Fig. 3) of CsPbBr3 PQDs shows three distinct peaks at approximately 15.1°, 21.5° and 30.5°, which can be attributed to the (100), (110) and (200) crystal planes, respectively. These peaks are consistent with the reference JCPDF No. 18-0364. Additionally, the composite films (CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP) also exhibit characteristic diffraction peaks from CsPbBr3 PQDs. This indicates that the CsPbBr3 PQDs have been successfully encapsulated in the polymer matrix, and their crystal structure remains intact without any damage.

    Figure 3

    Figure 3.  XRD patterns of the PBPP, PBEPP, pristine CsPbBr3 PQDs, CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP thin films.

    In the FT-IR spectrum of CsPbBr3 PQDs (Fig. 4) [31], the peaks observed at around 2925 cm−1 and 2847 cm−1 are attributed to the symmetric and antisymmetric C—H stretching vibrations, respectively. For CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP, the spectra show prominent characteristic peaks of CsPbBr3 PQDs, indicating the successful embedding of CsPbBr3 PQDs into PBPP and PBEPP polymers. For the PBPP, the peak at 1200 cm−1 is assigned to the —N=P— stretching vibration [32], while for the CsPbBr3 PQDs/PBPP, a blue shift of the —N=P— stretching vibration is observed at 1187 cm−1. Similarly, comparing the —N=P— stretching vibration peaks of PBEPP [33] and CsPbBr3 PQDs/PBEPP, a blue shift is also observed from 1200 cm−1 towards 1194 cm−1. This is due to the coordination effect between the N/P of the polyphosphazenes backbone and CsPbBr3 PQDs. In the PBPP infrared spectrum, the peak at 937 cm−1 is attributed to the stretching vibration of —P—O—, while in the CsPbBr3 PQDs/PBPP spectrum, this feature peak is blue-shifted to 919 cm−1. Similarly, comparing PBEPP and CsPbBr3 PQDs/PBEPP, the —P—O— peak shifts from 929 cm−1 to 933 cm−1, indicating the coordination effect between the oxygen in —P—O— and CsPbBr3 PQDs. In the FT-IR spectrum of PBEPP, the peak at 1719 cm−1 is assigned to the stretching vibration of —C=O—. In the CsPbBr3 PQDs/PBEPP spectrum, this peak is red-shifted to 1723 cm−1, which is attributed to the coordination betweenbase the —C=O— in the side groups of PBPP and CsPbBr3 PQDs [34]. The strong interactions between polymers (PBPP or PBEPP) and CsPbBr3 PQDs have effectively prevented the aggregation of PQDs in the polymer matrix and enabled their stable.

    Figure 4

    Figure 4.  FT-IR spectra of the PBPP, CsPbBr3 PQDs/PBPP, PBEPP and CsPbBr3 PQDs/PBEPP thin film.

    In order to further investigate the interactive mechanism between CsPbBr3 PQDs with polymers, XPS analysis was performed on CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP [31,34]. As shown in Fig. 5a, the high-resolution XPS spectrum of perovskite Br 3d can be deconvoluted into two peaks at 68.74 and 67.64 eV, which can be assigned to Br 3d5/2 and Br 3d3/2, respectively. However, in CsPbBr3 PQDs/PBPP, the corresponding binding energies of Br 3d5/2 and 3d3/2 are located at 69.04 eV and 67.94 eV, respectively. In CsPbBr3 PQDs/PBEPP, the binding energies are 69.45 and 68.35 eV, respectively, which have been shifted to higher field. The Pb 4f XPS spectra exhibits two peaks at 142.64 and 137.84 eV corresponding to Pb 4f5/2 and Pb 4f7/2, respectively (Fig. 5b). Similarly, in CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP, they have undergone a shift towards lower field at 140.44 eV (4f5/2), 135.54 eV (4f7/2) and 140.14 eV (4f5/2), 135.34 eV (4f7/2), respectively. Based on the electron shielding effect, as the electron density increases around an atom, the binding energy decreases accordingly. These results confirm that the interaction between CsPbBr3 PQDs with polymers has profound effect in electron environment around CsPbBr3, which leads to a decrease in the electron density of Pb and an increase in the electron density of Br. In addition, the side group structures of polymer have significant influence on the interaction between CsPbBr3 PQDs with polyphosphazenes. Strong molecular interaction is distinguished CsPbBr3 PQDs with PBEPP from CsPbBr3 PQDs with PBPP.

    Figure 5

    Figure 5.  (a) Br 3d and (b) Pb 4f XPS spectra of CsPbBr3, CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP thin film. (c, d) N 1s and (e, f) O 1s XPS spectra of CsPbBr3 PQDs/PBPP and PBPP thin film, CsPbBr3 PQDs/PBEPP and PBEPP thin film.

    In the CsPbBr3 PQDs/PBPP, the N 1s spectrum (Fig. 5c) can be divided into four major peaks at 397.65 eV (N=P), 398.15 eV (N—Br), 398.95 eV (N—Pb) and 402.75 eV (N+(CH3)3). The O 1s spectrum (Fig. 5e) exhibits three peaks at 533.15 eV (P—O), 533.95 eV (O—Pb) and 532.35 eV (O—Br). As displayed in Fig. 6, the results above indicate that there are hydrogen bond and coordination effect between Br/Pb from the PQDs and N/O in the main chain of the polyphosphazene [35]. This result is consistent with FT-IR spectra. Meanwhile, the N 1s and the O 1s spectra of the composite film shows the same binding energy of N=P and P—O—C with pure polymer, the chemical structure of polyphosphazenes in composite film does not change. Furthermore, similar behaviors are also observed in the O 1s and the N 1s spectra of CsPbBr3 PQDs/PBEPP (Figs. 5d and f).

    Figure 6

    Figure 6.  Schematic illustration of the interactions between PBPP and CsPbBr3 PQDs, PBEPP and CsPbBr3 PQDs.

    Fig. 7 shows the UV absorption and photoluminescence (PL) spectra of CsPbBr3 PQDs, CsPbBr3 PQDs/PBPP, and CsPbBr3 PQDs/PBEPP. The intrinsic emission peak of CsPbBr3 PQDs appears at 518 nm as green fluorescence. However, upon the location of PBPP and PBEPP matrix, the emission peak has shifted to 515 nm. The UV absorption peaks of CsPbBr3 PQDs, CsPbBr3 PQDs/PBPP, and CsPbBr3 PQDs/PBEPP are observed at 508, 506 and 506 nm, respectively. Therefore, the introduction of polyphosphazenes results in a slight blue shift in both emission and absorption wavelengths of CsPbBr3 PQDs. The decrease in emission wavelength indicates a smaller size of CsPbBr3 PQDs, which further explains that the steric effect related to substituents of polyphosphazenes and the interaction between Br/Pb and N/O together to inhibit the aggregation of the PQDs.

    Figure 7

    Figure 7.  PL and UV absorption spectra of CsPbBr3 PQDs, CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP thin film.

    To further investigate the impact of the interaction between CsPbBr3 and polyphosphazenes with different side-group structures on the excited state properties, the photoluminescence (PL) decay lifetime of different samples was measured using a time-resolved PL apparatus, and the charge recombination dynamics of CsPbBr3, CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP were studied (Fig. 8). Three exponential decay functions were used to fit all the curves, and the average PL lifetime of the samples was calculated using Eqs. 1 and 2. The detailed values of τ1, τ2 and τ3 are summarized in Table 1. The fastest lifetime (τ1) corresponds to the inherent radiative constant from the singlet excited state. In contrast, the other lifetimes (τ2 and τ3) are related to long-lived luminescence due to the multiple trapping and detrapping of carriers at the shallow trap states.

    (1)

    (2)

    Figure 8

    Figure 8.  PL lifetime curves of CsPbBr3, CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP.

    Table 1

    Table 1.  PL lifetime and fitted values of CsPbBr3 PQDs, CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP.
    DownLoad: CSV

    We observed that the average PL lifetimes (τavg) of CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP have decreased in comparison with the pristine CsPbBr3 PQDs: The τavg values of 8.87 ns and 14.14 ns are obtained in CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP, both of which are shorter than the τavg of 39.85 ns in the pristine CsPbBr3 PQDs. This result indicates that CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP composite films have a lower density of surface trap states and faster charge extraction rates compared to pristine CsPbBr3 PQDs [36]. This suggests that polyphosphazenes can effectively passivate surface defects of the perovskite and reduce energy loss. The charge transfer rate of CsPbBr3 PQDs/PBPP is higher than CsPbBr3 PQDs/PBEPP, which is because PBEPP can provide two coordination sites (phenoxy and ester). Therefore, the fluorescence lifetime of PBPP is shorter. These are consistent with the fact that the short-chain aromatic or conjugated ligands capped on PQDs can facilitate exciton delocalization. Fig. 8 illustrates the interfacial structures of CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP, where PBPP or PBEPP can suppress radiative recombination due to facilitation of migration and separation of photogenerated carriers.

    The polyphosphazene matrix forms a dense protection layer on the surface of PQDs, effectively inhibiting the interaction with surrounding environment and preventing structural damage. To evaluate the water resistance of the polyphosphazene-CsPbBr3 PQDs composite, the two samples have been dispersed in pure water directly for water stability testing. Periodic collection of the PL emissions of the two samples was conducted, and the spectra are shown in Figs. 9a and b. After immersing samples in water for 162 h, the fluorescence intensity of both samples has increased. In particular, CsPbBr3 PQDs/PBEPP exhibited a more pronounced increase of 10%. This can be attributed to the hydrophilic ester groups of PBEPP, which act as sacrificial layers, preventing water penetration into the active layer. Moreover, trace amounts of water can passivate the surface traps of CsPbBr3 PQDs and enhance the fluorescence intensity. As displayed in Figs. 9c and d, it can be observed that the fluorescence intensity of both composite films has no decrease after 30 days in air. However, there is a blue shift in the emission peak of CsPbBr3 PQDs/PBEPP, which could be attributed to the weaker hydrophobicity of PBEPP compared to PBPP. Oxygen and water in the air can result in the structural changes in CsPbBr3 PQDs, and thus leading to a blue shift of the emission peak.

    Figure 9

    Figure 9.  Long-term PL stability tests of (a) CsPbBr3 PQDs/PBPP and (b) CsPbBr3 PQDs/PBEPP films after soaking in water for 0–162 h. (c) CsPbBr3 PQDs/PBPP and (d) CsPbBr3 PQDs/PBEPP films PL spectra after keeping in the air for 0–30 days and their corresponding photographs under UV (365 nm) light.

    CsPbBr3 PQDs is regarded as an important material of light-emitting device, the structures are easily destroyed under high temperature conditions, which was an impediment to its application. Additionally, at higher temperatures, thermal stress amplifies the effects of oxygen, light, humidity and other environmental factors on CsPbBr3 PQDs. The different composite films were kept at 25, 60, 90, 120 and 150 ℃ for 10 min and cooled down to room temperature. Then thermal stability of the film was tested. As shown in PL testing results (Fig. 10a), it can be seen that as the temperature increases, the fluorescence intensity of CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP exceeded the original fluorescence intensity. The fluorescence intensity of CsPbBr3 PQDs/PBPP increased by up to 98% at 120 ℃, and the fluorescence intensity of CsPbBr3 PQDs/PBEPP increased by up to 98% at 150 ℃. This indicates that polyphosphazenes, as a polymer matrix, can improve the thermal stability of CsPbBr3 PQDs. The fluorescence enhancements of PBEPP are more outstanding at higher temperature. Such enhancement is related to the high charge transfer ability of the aryloxy group in polyphosphazenes, which effectively receives excitation energy from CsPbBr3 and transfers it to polyphosphazenes. The interaction between the C=O group in PBEPP with CsPbBr3 enhances the energy transfer mechanism above 120 ℃, resulting in stronger fluorescence intensity. The poor photostability of PQDs also limits their practical applications in the optoelectronics field. Long-term exposure to UV light, PQDs can cause halide ion migration, which further leading to ligand dissociation and crystal regeneration. Fig. 10b shows the fluorescence intensity of both CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP gradually increases by 46.5% and 7%, respectively, upon 365 nm UV light irradiation for 2 h [37,38]. This can be attributed to the UV resistance characteristics of polyphosphazenes, which effectively protects CsPbBr3. The photoinduction effect enhances the passivation of trap states in polyphosphazene, which could suppress non-radiative recombination and quenching phenomena [37,38]. Due to the coordination structure between PBPP-CsPbBr3 and PBEPP-CsPbBr3, CsPbBr3 PQDs/PBPP exhibits a stronger photoinduction effect on CsPbBr3 compared to CsPbBr3 PQDs/PBEPP.

    Figure 10

    Figure 10.  Long-term stability tests of the CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP thin film. (a) PL intensity under UV (365 nm) light at 25, 60, 90, 120 and 150 ℃ for 10 min. (b) PL intensity after keeping under 365 nm UV light for 2 h.

    In conclusion, by employing linear polyphosphazenes with phenoxy or 4-ester-phenoxy as pendent groups, we have successfully encapsulated CsPbBr3 PQDs in flexible polymer films, namely CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP. These composite films exhibit excellent dispersion of PQDs, optical transparency and stability in various extreme conditions. The different coordinating groups provided by polyphosphazenes side group lead to various effects on the optical performance and stability of CsPbBr3 PQDs. CsPbBr3 PQDs/PBPP demonstrates excellent air and light stabilities, while CsPbBr3 PQDs/PBEPP shows superior water and thermal resistances. Both composite films all maintain stable fluorescence after a 30-day air storage, but the emission wavelength of CsPbBr3 PQDs/PBEPP shifts towards the blue. Under UV (365 nm) light, the fluorescence intensity of both films is improved. CsPbBr3 PQDs/PBEPP display a greater increase than CsPbBr3 PQDs/PBPP in fluorescence intensity. And CsPbBr3 PQDs/PBEPP also shows a 10% increase in fluorescence intensity after 96 h of water immersion, while CsPbBr3 PQDs/PBPP remains stable. Moreover, under high temperature conditions, the fluorescence intensity of obtained composite film is stronger than room temperature, CsPbBr3 PQDs/PBEPP showing a 98% increase at 150 ℃. Therefore, these composite films demonstrate promising capabilities in preventing humidity, UV radiation, oxygen and heat, and holding a strong potential for photo functional and optical applications.

    The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

    This work is supported by the National Science Foundation (NSF) of China (No. 51773010), the Weifang Science and Technology Development Plan Program (No. 2023GX005).

    Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2024.109795.


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  • Scheme 1  Schematic illustration of preparation of CsPbBr3/polyphosphazene thin films.

    Figure 1  Photographs of (a, d) CsPbBr3 PQDs/PBPP-toluene and CsPbBr3 PQDs/PBEPP-toluene. (b, e) CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP thin films. (c, f) CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP thin films after bending. (a-c) Under daylight and (d-f) under UV (365 nm) light, respectively.

    Figure 2  Fluorescence images of (a) CsPbBr3 PQDs/PBPP and (b) CsPbBr3 PQDs/PBEPP thin film.

    Figure 3  XRD patterns of the PBPP, PBEPP, pristine CsPbBr3 PQDs, CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP thin films.

    Figure 4  FT-IR spectra of the PBPP, CsPbBr3 PQDs/PBPP, PBEPP and CsPbBr3 PQDs/PBEPP thin film.

    Figure 5  (a) Br 3d and (b) Pb 4f XPS spectra of CsPbBr3, CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP thin film. (c, d) N 1s and (e, f) O 1s XPS spectra of CsPbBr3 PQDs/PBPP and PBPP thin film, CsPbBr3 PQDs/PBEPP and PBEPP thin film.

    Figure 6  Schematic illustration of the interactions between PBPP and CsPbBr3 PQDs, PBEPP and CsPbBr3 PQDs.

    Figure 7  PL and UV absorption spectra of CsPbBr3 PQDs, CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP thin film.

    Figure 8  PL lifetime curves of CsPbBr3, CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP.

    Figure 9  Long-term PL stability tests of (a) CsPbBr3 PQDs/PBPP and (b) CsPbBr3 PQDs/PBEPP films after soaking in water for 0–162 h. (c) CsPbBr3 PQDs/PBPP and (d) CsPbBr3 PQDs/PBEPP films PL spectra after keeping in the air for 0–30 days and their corresponding photographs under UV (365 nm) light.

    Figure 10  Long-term stability tests of the CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP thin film. (a) PL intensity under UV (365 nm) light at 25, 60, 90, 120 and 150 ℃ for 10 min. (b) PL intensity after keeping under 365 nm UV light for 2 h.

    Table 1.  PL lifetime and fitted values of CsPbBr3 PQDs, CsPbBr3 PQDs/PBPP and CsPbBr3 PQDs/PBEPP.

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  • 发布日期:  2025-04-15
  • 收稿日期:  2024-01-31
  • 接受日期:  2024-03-19
  • 修回日期:  2024-03-13
  • 网络出版日期:  2024-03-19
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