CsPbBrxI3-x全无机钙钛矿量子点的组分及浓度对电子结构及荧光性质影响研究

doi:10.6023/A24030066

摘要/Abstract

全无机铯-卤化铅钙钛矿材料因其优异的性能在光电领域具有广泛的应用前景. 本工作通过第一性原理计算和稳态、瞬态荧光光谱实验研究了CsPbBr_xI_3-_x (x=3, 2, 1, 0)全无机钙钛矿量子点卤素组分和量子点浓度对其电子结构及荧光性质影响规律. 通过对材料CsPbBr_xI_3-_x进行能带结构和态密度的计算, 发现这种钙钛矿的带隙类型都为直接带隙, 带隙值随着I原子的不断取代, 带隙变窄, 表明了可通过增加I含量来实现量子点的能带调控. 通过对CsPbBr₃和CsPbBr₂I全无机钙钛矿量子点进行稳态发光和皮秒时间分辨单光子计数实验, 发现随着量子点浓度的增加, 发射光谱红移, 光致发光强度先增大后减小, 荧光辐射寿命增加. 这些现象主要是由于量子点的量子限制效应以及自吸收效应导致的. 随着量子点的浓度增加, 量子点因发生团聚效应而尺寸增大, 导致发射光谱红移. 当量子点浓度大到一定程度时, 量子点的吸光度逐渐饱和, 自吸收效应会使发射荧光部分被吸收, 导致荧光发射强度先增大后减小. 随着钙钛矿量子点浓度的增加, 量子限制效应导致量子点团聚, 尺寸增大, 进而使其荧光辐射寿命增加. 随着I含量的增加, 量子点捕获态产生导致晶体结构的扭曲, 因而荧光寿命变短. 这些结果表明激子重组过程可通过调节浓度和卤素组分进行控制.

关键词: 全无机钙钛矿, 电子结构, 光致发光, 辐射寿命, 卤素组分, 尺寸依赖

All-inorganic cesium lead halide perovskite materials have broad application prospects in the field of optoelectronics due to their excellent performance. The influences of component and concentration on the electronic structure and fluorescence properties of the CsPbBr_xI_3-_x (x=3, 2, 1, 0) all-inorganic perovskite quantum dots using the first-principles calculations and steady-state and transient fluorescence spectroscopy experiments were investigated. The band structure and density of states of the perovskites CsPbBr_xI_3-_x are calculated to find that the bandgap types are all direct bandgaps and the bandgap becomes narrow with the continuously supplanting of I atoms. This indicates that increasing the I content can achieve the band gap regulation of quantum dots. The steady-state luminescence and picosecond time-correlated single photon counting experiments are completed for CsPbBr₃ and CsPbBr₂I all-inorganic perovskite quantum dots, it is found that with the increase of quantum dot concentration, the emission spectrum is red-shifted, the photoluminescence intensity first increases and then decreases, and the fluorescence radiation lifetime also increases. These phenomena are mainly caused by the quantum confinement effect and self-absorption effect of quantum dots. As the concentration of quantum dots increases, the size of quantum dots increases due to agglomeration effects, resulting in a red shift in the emission spectrum. When the concentration of quantum dots reaches a certain level, the absorbance of quantum dots gradually saturates, and the self-absorption effect will cause the emission of fluorescence to be absorbed, leading to an increase and then a decrease in fluorescence emission intensity. As the concentration of perovskite quantum dots increases, the quantum confinement effect leads to the size increase of quantum dots due to the aggregation effect, thereby increasing their fluorescence radiation lifetime. With increasing I content, the quantum dot trapping states lead to a distortion of the crystal structure, and thus the fluorescence lifetime becomes short. These results suggest that the exciton recombination process can be controlled by regulating concentration and halogen components.

Key words: all-inorganic perovskite, electric structure, photoluminescence, radiative lifetime, halogen component, size dependence

引用此文

彭亚晶, 赵雨新, 杨金辉, 仉昕昕, 程佳玲. CsPbBr_xI_3-_x全无机钙钛矿量子点的组分及浓度对电子结构及荧光性质影响研究[J]. 化学学报, 2024, 82(8): 879-886.

Yajing Peng, Yuxin Zhao, Jinhui Yang, Xinxin Zhang, Jialing Cheng. Study on the Influence of Component and Concentration of CsPbBr_xI_3-x All-inorganic Perovskite Quantum Dots on Electronic Structure and Fluorescence Properties[J]. Acta Chimica Sinica, 2024, 82(8): 879-886.

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图/表 15

图1. CsPbBrxI3-x晶体结构图

Figure 1. Crystal structure of CsPbBrxI3-x

量子点	对称点	×b₁	×b₂	×b₃
CsPbBr₃ CsPbI₃	Γ	0	0	0
	M	1/2	1/2	0
	R	1/2	1/2	1/2
	X	0	1/2	0
CsPbBr₂I CsPbBrI₂	Γ	0	0	0
	A	1/2	1/2	1/2
	M	1/2	1/2	0
	R	0	1/2	1/2
	X	0	1/2	0
	Z	0	0	1/2

表1. 量子点高对称点倒空间坐标

Table 1. Inverted space coordinates of high symmetry points of quantum dots

图2. CsPbBr3钙钛矿量子点的透射电子显微镜(TEM)图

Figure 2. TEM image of CsPbBr3 perovskite quantum dots

图3. 稳态发光实验过程图

Figure 3. Steady-state luminescence experimental process diagram

图4. 荧光辐射寿命实验过程图

Figure 4. Fluorescence radiation lifetime experimental process diagram

结构名称	晶格参数			体积 V/a.u.	总能量 E/eV
结构名称	a/nm	b/nm	c/nm	体积 V/a.u.	总能量 E/eV
CsPbBr₃	0.598	0.598	0.598	428.34	－15.93
CsPbBr₂I(Ⅰ)	0.599	0.641	0.641	491.32	－15.30
CsPbBr₂I(Ⅱ)	0.597	0.641	0.641	490.56	－14.69
CsPbBrI₂(Ⅰ)	0.603	0.638	0.638	490.95	－15.77
CsPbBrI₂(Ⅱ)	0.641	0.599	0.599	459.47	－15.29
CsPbI₃	0.640	0.640	0.640	523.43	－14.09

表2. 优化的CsPbBrxI3-x晶体结构参数

Table 2. Optimized CsPbBrxI3-x crystal structure parameters

图5. 用DFT-PBE方法计算的能带结构图

Figure 5. Band structure calculated by DFT-PBE method

结构名称	价带顶 E_v/eV	导带底 E_c/eV	带隙值 E_g/eV	文献带隙值
结构名称	价带顶 E_v/eV	导带底 E_c/eV	带隙值 E_g/eV	计算E_g/eV	实验E_g/eV
CsPbBr₃	－0.21	1.54	1.75	1.78^[41]	2.30^[42]
CsPbBr₂I(I)	－0.21	1.33	1.54	1.47^[43]
CsPbBr₂I(Ⅱ)	－0.23	1.32	1.55	1.47^[43]
CsPbBrI₂(I)	－0.21	1.32	1.53	1.47^[41]
CsPbBrI₂(Ⅱ)	－0.24	1.29	1.53	1.47^[41]
CsPbI₃	－0.21	1.28	1.49	1.45^[41]	1.7^[44]

表3. 价带顶和导带底的能量以及计算的带隙值

Table 3. The energy of valence band maximum and conduction band minimum and the calculated band gap values Eg

图6. CsPbBrxI3-x无机钙钛矿的总态密度

Figure 6. Total density of states of CsPbBrxI3-x inorganic perovskites

图7. 用DFT-PBE方法计算的分态密度(PDOS)和总态密度(TDOS)

Figure 7. Partial density of states (PDOS) and total density of states (TDOS) calculated by DFT-PBE method

图8. 不同浓度CsPbBr3 (a)和CsPbBr2I (b)溶液的稳态发射光谱

Figure 8. Steady-state emission spectra of CsPbBr3 (a) and CsPbBr2I (b) solutions at different concentrations

图9. 不同浓度CsPbBr3量子点的SEM图

Figure 9. SEM images of different concentration CsPbBr3 quantum dots

钙钛矿	浓度 C/(mg•mL⁻¹)	波长 λ/nm	发射光谱曲线积分Intensity/ a.u.	光强峰值Intensity/a.u.
CsPbBr₃	0.1	505.82	18.43	0.69
	0.5	508.23	19.97	0.75
	1.0	509.36	17.85	0.52
	2.5	512.24	11.09	0.43
CsPbBr₂I	0.1	521.90	19.70	0.29
	0.5	522.67	30.89	0.88
	1.0	525.80	29.25	0.82
	2.5	531.25	18.38	0.23

表4. 不同浓度CsPbBr3和CsPbBr2I溶液的发射波长与发射光谱曲线积分(积分区间取450~600 nm)和荧光强度峰值

Table 4. The emission wavelength, integration of emission spectra curves and emission peak intensity of different concentrations of CsPbBr3 and CsPbBr2I solutions

图10. 不同浓度CsPbBr3 (a)和CsPbBr2I (b)溶液荧光辐射寿命曲线及拟合

Figure 10. Fluorescence radiation lifetime curves and the corresponding fitting of CsPbBr3 (a) and CsPbBr2I (b) solutions at different concentrations

	C/(mg•mL⁻¹)	τ₁/ns	A₁/%	τ₂/ps	A₂/%	τ_ave/ns
CsPbBr₃	0.1	1.489	0.501	8.003	0.499	6.978
	0.5	2.015	0.412	10.931	0.588	9.911
	1.0	2.217	0.540	11.973	0.460	10.231
	2.5	1.491	0.477	14.256	0.523	13.144
CsPbBr₂I	0.1	0.790	0.216	2.945	0.784	2.797
	0.5	4.895	0.497	4.894	0.503	4.894
	1.0	6.060	0.933	0.282	0.067	6.041
	2.5	0.477	0.054	6.748	0.946	6.723

表5. 不同浓度CsPbBr3和CsPbBr2I钙钛矿量子点的荧光辐射寿命拟合参数

Table 5. The fitting parameters of fluorescence radiation lifetime for CsPbBr3 and CsPbBr2I perovskite quantum dots with different concentrations

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