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This study tackles the significant challenge of phase separation in mixed halide (Br–/Cl–) perovskite systems, which severely affects the spectral stability of blue perovskite light-emitting diodes (PeLEDs). A compositional engineering strategy is proposed, precisely controlling the Cs:Pb molar ratio (1∶1 to 1.1∶1) in precursor solutions to construct a CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6 composite phase structure. Transmission electron microscopy (TEM) mapping and X-ray diffraction (XRD) analysis confirm that Cs4Pb(Br1–xClx)6 nanocrystals (5–8 nm in diameter) grow in situ and uniformly encapsulate CsPb(Br1–xClx)3 microparticles (50–100 nm). This composite architecture has double functional advantages: 1) the Cs4PbX6 shell acts as a physical barrier, reducing halide ion migration activation energy and suppressing phase segregation during continuous operation; 2) the wide-bandgap (3.9–4.3 eV) Cs4PbX6 induces quantum confinement effects, confining carriers within CsPbX3 while passivating defect states, thereby improving perovskite performance. The optimized PeLED achieves notable improvements in brightness, external quantum efficiency, and operational stability, maintaining stable emission at 478 nm under a 50 mA/cm² current density. This is achieved by inhibiting halide phase separation and enhancing the efficiency of carrier recombination achieved by the cesium-lead halide heterojunction system. This work provides fundamental insights into phase-stable perovskite design via composite crystallization kinetics, providing a viable pathway toward commercial-grade blue PeLEDs for full-color displays.
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Keywords:
- perovskite /
- blue light /
- light-emitting diode (LED)
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图 1 (a) CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6钙钛矿器件的能级图; (b), (c) Cs/Pb = 1和Cs/Pb = 1.1的钙钛矿薄膜的XRD图谱; (d), (g) Cs/Pb = 1和Cs/Pb = 1.1的钙钛矿薄膜的TEM图像, 比例尺为200 nm; (e), (h) Cs/Pb = 1和Cs/Pb = 1.1的钙钛矿薄膜的TEM图像, 比例尺为50 nm; (f), (i) Cs/Pb = 1和Cs/Pb = 1.1的钙钛矿薄膜的高分辨透射电子显微镜(HRTEM)图像, 比例尺为5 nm, 其对应的快速傅里叶变换(FFT)图案显示在左上角
Figure 1. (a) Energy level diagram of the CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6 perovskite device; (b), (c) XRD patterns of perovskite films with Cs/Pb = 1 and Cs/Pb = 1.1, respectively; (d), (g) TEM images of perovskite films with Cs/Pb = 1 and Cs/Pb = 1.1, respectively, at a scale bar of 200 nm; (e), (h) TEM images of perovskite films with Cs/Pb = 1 and Cs/Pb = 1.1, respectively, at a scale bar of 50 nm; (f), (i) HRTEM images of perovskite films with Cs/Pb = 1 and Cs/Pb = 1.1, respectively, at a scale bar of 5 nm, with their corresponding fast Fourier transform (FFT) patterns shown in the upper left corner.
图 2 混合卤化物钙钛矿化合物CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6的光致发光(PL)特性 (a) x = 0.1时的PL光谱; (b) x = 0.2时的PL光谱; (c) x = 0.3时的PL光谱; (d) x = 0.4时的PL光谱
Figure 2. Photoluminescence (PL) mixed-halide perovskite compounds CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6: (a) PL spectrum for x = 0.1; (b) PL spectrum for x = 0.2; (c) PL spectrum for x = 0.3; (d) PL spectrum for x = 0.4.
图 3 混合卤化物钙钛矿化合物CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6在温度从290 K降至150 K时的温度依赖性光致发光(PL)光谱 (a) x = 0.1时的PL光谱; (b) x = 0.2时的PL光谱; (c) x = 0.3时的PL光谱; (d) x = 0.4时的PL光谱
Figure 3. Temperature-dependent photoluminescence (PL) spectra of mixed-halide perovskite compounds CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6 as the temperature decreases from 290 to 150 K: (a) PL spectrum for x = 0.1; (b) PL spectrum for x = 0.2; (c) PL spectrum for x = 0.3; (d) PL spectrum for x = 0.4.
图 4 混合卤化物钙钛矿化合物CsPb(Br1–xClx)3和CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6在电流密度为50 mA/cm²时测量的电致发光(EL)光谱 (a), (b) CsPb(Br1–xClx)3和CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6在x = 0.1时的EL光谱; (c), (d) CsPb(Br1–xClx)3和CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6在x = 0.2时的EL光谱; (e), (f) CsPb(Br1–xClx)3和CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6在x = 0.3时的EL光谱; (g), (h) CsPb(Br1–xClx)3和CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6在x = 0.4时的EL光谱
Figure 4. Electroluminescence (EL) spectra of mixed-halide perovskite compounds CsPb(Br1–xClx)3 and CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6 measured under a current density of 50 mA/cm²: (a), (b) EL spectra of CsPb(Br1–xClx)3 and CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6 at x = 0.1, respectively; (c) and (d) EL spectra of CsPb(Br1-xClx)3 and CsPb(Br1-xClx)3/Cs4Pb(Br1-xClx)6 at x = 0.2, respectively; (e), (f) EL spectra of CsPb(Br1–xClx)3 and CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6 at x = 0.3, respectively; (g), (h) EL spectra of CsPb(Br1–xClx)3 and CsPb(Br1–xClx)3/Cs4Pb(Br1–xClx)6 at x = 0.4, respectively.
图 5 (a), (b) Cs/Pb = 1和Cs/Pb = 1.1时CsPb(Br1–xClx)3的J-V曲线; (c), (d) Cs/Pb = 1和Cs/Pb = 1.1时CsPb(Br1–xClx)3的J-L曲线; (e), (f) Cs/Pb = 1和Cs/Pb = 1.1时CsPb(Br1–xClx)3的EQE曲线; (g), (h) Cs/Pb = 1和Cs/Pb = 1.1在50 mA/cm2电流密度下CsPb(Br1–xClx)3寿命曲线
Figure 5. (a), (b) J–V curves of CsPb(Br1–xClx)3 with Cs/Pb = 1 and Cs/Pb = 1.1, respectively; (c), (d) J–L curves of CsPb(Br1–xClx)3 with Cs/Pb = 1 and Cs/Pb = 1.1, respectively; (e), (f) external quantum efficiency (EQE) curves of CsPb(Br1–xClx)3 with Cs/Pb = 1 and Cs/Pb = 1.1, respectively; (g), (h) lifetime curves of CsPb(Br1–xClx)3 with Cs/Pb = 1 and Cs/Pb = 1.1 measured at a current density of 50 mA/cm2, respectively.
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