East China Institute of Technology achieves high luminous brightness and high stability of circular polarized perovskite luminescence

Recently, Matter officially published the research results of Professor Zhu Weihong, Professor Wu Yongzhen and Professor Zheng Zhigang of the School of Chemistry and Molecular Engineering of East China University of Science and Technology in the field of circular polarized perovskite luminescence research” “Circularly Polarized Perovskite Luminescence with Dissymmetry Factor up to 1.9 by Soft Helix Bilayer Device”.

This work solves the compatibility problem of perovskite and liquid crystal with double-layer structure by stabilizing perovskites with polymers and constructing perovskite-liquid crystal devices (PeLC), improves the luminescence efficiency and stability of perovskites, and ensures the orderly arrangement and dynamic tunable performance of liquid crystal molecules, and realizes the luminescence of circular polarized perovskites with high luminescence brightness and high stability. Its asymmetric factor (glum) is as high as 1.9, close to the theoretical limit of 2.0, based on the structure of the device to show the circular polarization light pattern display and temperature control anti-counterfeiting applications, the work to achieve high-quality circular polarized perovskite luminescence and its device application opened up a new idea.

The first authors of the paper are Liu Shuaijun, a doctoral student in the School of Chemistry and Molecular Engineering, and Liu Xuan, a doctoral student in the School of Physics.

Circular polarized luminescence (CPL) refers to the phenomenon that the luminous system emits differential left-handed and right-handed circular polarized light, which has a wide range of application prospects in the fields of three-dimensional display, biological sensing, encryption anti-counterfeiting, and photocatalytic asymmetric synthesis. Metal halide perovskite materials have excellent characteristics such as high fluorescence quantum efficiency, narrow emission peak, and adjustable emission wavelength, which is expected to become an ideal CPL new material. At present, the reported perovskite CPL materials (such as chiral two-dimensional perovskites, chiral ligand modified perovskite nanocrystals, etc.) have problems such as small asymmetric factors (glum values) and low luminescence efficiency, and their stability has rarely been studied, which seriously limits its practical application. The incorporation of perovskite nanocrystals into the enterocular facade liquid crystal can significantly improve the gum value of CPL, but the mixed system will not only seriously damage the structural stability of the perovskite, but also affect the orderly arrangement of liquid crystal molecules and weaken its circular polarization modulation ability to light. Therefore, how to obtain CPL with high luminous efficiency and high gum value still faces great challenges.

Highlights of this article

The fluorescence quantum efficiency (PLQY) of perovskite-polyacrylonitrile (PAN) film can reach 97.5%, and can be stably placed in water for more than 30 days;

The PeLC double-layer structure device is constructed, and the high-quality perovskite CPL is realized, and its gum value is as high as 1.9;

A variety of device-based patterning processes are reported, demonstrating the dynamic properties of CPL that change with temperature reversibility.

Screening polymer matrix improves perovskite luminescence efficiency and stability.Compared with traditional ligand-modified perovskite quantum dots, the polymer matrix has excellent limiting effects and environmental stability, which can significantly improve the luminescence performance and structural stability of perovskite nanocrystals. By screening the polymer structure, the authors found that PAN plays a crucial role in the crystallization process of perovskite nanocrystals. Perovskite films prepared based on this strategy have a PLQY of up to 97.5 ±1%, and soaking them in water for 30 days can still maintain 93.3% of the initial PLQY. Studies have shown that excellent luminescence and stability are mainly due to the high density of polymers, environmental inertness and the effective passivation ability of their side chain groups to perovskite nanocrystalline defects.

Figure 1: Preparation and characterization of MAPbBr3-PAN films

The two-layer structure device realizes CPL with high gum value and high luminous efficiency.By combining the perovskite-PAN film with the chiral facade liquid crystal, the author constructs a PeLC bilayer structural device. Compared with the method of directly mixing perovskite quantum dots and liquid crystals, the construction of this bilayer structure not only ensures the high luminescence efficiency and stability of perovskites, but also avoids the disruption of the orderliness of the optical microstructure of liquid crystals, thus perfectly retaining the optical and stimulus response characteristics of liquid crystals. Based on the above advantages, PeLC devices can achieve very bright CPL, with a gum value of up to 1.9, approaching the theoretical limit of 2.0, and the device shows more than half a year of storage stability.

Figure 2: Construction and characterization of PeLC bilayer devices and hybrid devices

CPL wavelength tuning and device patterning.Due to the advantages of perovskites with adjustable wavelengths, the authors successfully realized perovskite CPL with different emission wavelengths (red, green, blue) by adjusting the halogen components of perovskites, glum values up to 1.7-1.9; at the same time, thanks to the processability of perovskites and PAN solutions, the authors also demonstrated a series of perovskite-PAN film preparation strategies (such as laser etching, mask plate spin coating, etc.), thus successfully constructing fine patterned PeLC devices. Based on the above characteristics, this patterned color device shows great application potential in the field of CPL display.

Figure 3: Preparation and display of patterned color PeLC bilayer devices

Temperature-controlled dynamic reversible CPL.Thanks to the stimulative response of chiral phase liquid crystals to temperature, the CPL signal of PeLC devices also exhibits dynamic characteristics that change reversibly with temperature. Combined with the above pattern preparation process, the author uses a circular polarizer to demonstrate the change of CPL of a two-dimensional code device with temperature, which provides a new idea for how to intuitively detect the circular polarization characteristics of the light-emitting device. It is worth mentioning that the use of this strategy in the field of anti-counterfeiting can significantly enhance the concealment of anti-counterfeiting information and further enhance its application potential in high-end anti-counterfeiting.

Figure 4: Temperature-responsive reversible CPL for anti-counterfeiting applications

Based on the polymer embedded perovskite material and chiral phase liquid crystal, the perovskite CPL with high gum value, high luminescence efficiency and high stability was successfully realized. By stabilizing perovskite nanocrystals, perovskite-PAN films exhibit 97.5% PLQY and water stability of more than 30 days. The perovskite-PAN film was further combined with the chiral facade liquid crystal to successfully construct the PeLC bilayer device, which achieved a bright and stable CPL with a glum value of up to 1.9. In addition, this paper also reports the patterned CPL with adjustable emission wavelength and the dynamic reversible regulation of the CPL signal by adjusting the temperature. This research work has important guiding significance for how to improve the luminescence efficiency, glum value and stability of perovskite materials and deviceSCPL at the same time, and demonstrates the application potential of perovskite materials in the field of CPL. (Source: Science Network)

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