Deconvoluting the energy transport mechanisms in all-inorganic CsPb2Br5/CsPbBr3 perovskite composite systems

Yunpeng Wang,Yi Fan,Quan Quan,Gangbei Zhu,Zhengxun Lai,Fei Wang,You Meng,Dongxu Zhao,Johnny C Ho,Senpo Yip

doi:10.1063/5.0083022

Abstract

CsPb2Br5/CsPbBr3 composite systems have received considerable attention among numerous lead halide perovskite materials due to their significantly enhanced photoluminescence intensity and stability against moisture. However, the luminescence mechanism of CsPb2Br5 based materials remains controversial, which significantly hinders the further material design and utilization for optoelectronic devices. In this work, to deconvolute their luminescent mechanisms, high-quality CsPb2Br5 crystals without any undesired by-products and impurities have been first prepared by a microwave-assisted synthesis method. The luminescence-inactive characteristics of the material are then confirmed by the steady-state absorption, photoluminescence, transient absorption spectra, and time-resolved terahertz spectroscopy. The prepared CsPb2Br5 crystals exhibit excellent crystallinity and enhanced thermal stability, particularly that they can maintain their crystalline structures in polar organic solvents. By simply manipulating the ratios of different precursor materials, it is witnessed that the green emission comes from the CsPbBr3 adhered, nucleated, and grown on the CsPb2Br5 crystals. Ultrafast transient absorption measurements in visible and terahertz spectral regions reveal that with the help of phonon scattering-assisted hopping at interfacial states, intersystem crossing dominates the electron transfer process in the composite crystals. As a result, the CsPb2Br5 and CsPbBr3 interact extensively with each other. Meanwhile, the Auger recombination rate and the defect-related non-radiative process are suppressed in the composite crystals, thereby enhancing the fluorescence of composite crystals. This work has not only deconvoluted the controversial and unclear luminescent mechanisms of CsPb2Br5 materials but also established a pathway to design and enhance the fluorescence of materials for technological applications.

Highlights

When the precursor molar ratio is slightly increased from 0.5:1 (CsBr:PbBr2) to 0.6:1, some yellow patches begin to appear on the surface of the CsPb2Br5 crystal [Fig. 1(b)]
Single-phase high-quality CsPb2Br5 crystals have been successfully prepared by a microwave-assisted synthesis method
By characterizing and investigating the fluorescent activities of the samples prepared with different ratios of precursor materials, it is found that the green emission comes from the CsPbBr3 adhered, nucleated, and grown on the CsPb2Br5 crystals

Summary

Introduction

Cesium lead bromide (Cs–Pb–Br) perovskites are excellent candidate materials for next-generation lighting and display devices due to their superb properties of highly efficient and stable luminescence, narrow fluorescent line widths, and tunable emission wavelengths.1–3 Typically, there are three main structures explored and reported for Cs–Pb–Br perovskites: CsPbBr3, CsPb2Br5, and Cs4PbBr6, which can be obtained by changing the stoichiometry ratio between CsBr and PbBr2 precursors during the scitation.org/journal/apm synthetic process.4 Until now, extensive research efforts have been dedicated to examining and deciphering the structural, optical, and electronic properties of these three perovskite materials.5–11 It is worth mentioning that the synthesized CsPb2Br5/CsPbBr3 composite structures have shown the increased photoluminescence (PL) intensity arising from the dielectric confinement of CsPb2Br5 material and present the much-enhanced stability against moisture owing to the water-resistant characteristics of the CsPb2Br5 matrix.8 These CsPb2Br5/CsPbBr3 perovskite complexes can almost keep their initial PL intensity after four months of storage in an ambient atmosphere.5 They can even retain their high PL quantum yields and narrow-band emissions in water solutions.6 In this regard, the CsPb2Br5 and CsPb2Br5/CsPbBr3 composite materials have become a hot research topic for their potential possibilities to resolve the instability issues of perovskites, drawing substantial attention in recent years.9. Ultrafast transient absorption measurements in visible and terahertz spectral regions reveal that with the help of phonon scattering-assisted hopping at interfacial states, intersystem crossing dominates the electron transfer process in the composite crystals.

Results

Conclusion