Multifunctional ligands synergistically improve the optoelectronic properties of CsPbI3 nanocrystals to achieve high-performance red PeLED

• Inorganic lead halide perovskite nanocrystals (LHP NC s) are considered to be ideal luminescent materials for active-matrix nanocrystal light-emitting diodes (LEDs ) due to their high defect tolerance, narrow half-width (FWHM) and wide color gamut (covering almost 100% of Rec. 2020). With the continuous optimization of perovskite light-emitting layer preparation technology and device structure, perovskite LEDs (PeLEDs) based on CsPb X3 (X = Cl, Br, I) NCs have made significant progress in just a few years, with external quantum efficiencies (EQEs) exceeding 20%. However, the unstable surface of LHP NCs makes them prone to degradation, limiting their further development and application.

  
  

  At present, the main problems of CsPbI3NCs include: on the one hand, the binding force of ligands on the surface of CsPbI3NCs is weak, and the binding of oleic acid and oleylamine (OA and OAm) ligands to CsPbI3NCs is in a dynamically unstable state, which easily produces non-radiative recombination centers, degrading the optical properties and stability of CsPbI3NCs. On the other hand, the insulating properties of OA and OAm inhibit the injection and transport of carriers, thereby degrading device performance and reducing the efficiency and stability of PeLEDs. Therefore, there is an urgent need for a multifunctional ligand that can achieve efficient defect passivation and improve carrier transport performance, thereby comprehensively improving the efficiency and operational stability of PeLEDs.

  
  

  In view of this, Song Jizhong, Yao Jisong and others from Zhengzhou University proposed a method of post-treatment with 2-thiopheneethylamine chloride (TEAC) ligand to reshape the surface of CsPbI3 NCs and synergistically improve the optical and electrical properties of CsPbI3 NCs, so as to construct high-performance red light PeLEDs. After TEAC treatment, the defect density in CsPbI3 NCs was significantly reduced. Benefiting from these results, TEAC-modified CsPbI3 NCs still maintained a high PLQY (92.5%) after two purification processes (see Figure 1). Surface analysis and theoretical calculations proved that TEAC was anchored on the surface of CsPbI3 NCs in a bidentate form, and TEA+ could simultaneously interact strongly with uncoordinated Pb2+ and I− (see Figure 2), inhibiting non-radiative convergence and effectively improving the stability of CsPbI3 NCs (see Figure 3). At the same time, the TEAC ligands containing thiophene groups partially replaced the long-chain aliphatic ligands on the surface of CsPbI3 NCs, improving the carrier transport properties of NCs (see Figure 4). The red light PeLED constructed based on this achieved an external quantum efficiency (EQE) of 17.3% at 687 nm of emitted light, and T50 was as high as 9.8 h (see Figure 5). The surface engineering based on the above TEAC fully illustrates that screening ligands with both high conductivity and strong coordination is crucial for the preparation of efficient and stable PeLEDs.

  
  

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• Figure 1. TEAC surface treatment improves the luminescence properties of NCs
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• Figure 2. Mechanism of TEAC passivation of CsPbI3 NCs

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• Figure 3. TEAC improves the stability of CsPbI3 NCs

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• Figure 4. TEAC improves the electrical properties and film-forming properties of CsPbI3 NCs

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• Figure 5. Device performance of PeLED.

• Li Chuang, Yao Jisong*, Xu Leimeng, Yang Zhi, Wang Shalong, Cai Bo*, Wang Jindi, Fan Wenxuan, Wang Yu*, Song Jizhong*. Multifunctional ligand-manipulated luminescence and electric transport of CsPbI3perovskite nanocrystals for red light-emitting diodes.

  
  

  DOI : 10.1016/j.cej.2024.152483

  
  

  https://doi.org/10.1016/j.cej.2024.152483.