The research team of Harbin Institute of Technology achieves efficient pure blue perovskite LED through synergistic dual passivation of indium doping and zwitterionic ligands

Lead halide perovskite nanocrystals have attracted widespread attention in perovskite based light-emitting diodes due to their high photoluminescence quantum yield, tunable emission spectra, excellent color purity, and ease of solution processing. In order to meet the requirements of the National Television System Committee standards, the development of pure blue PeLEDs with emission wavelengths of 460-470 nm has aroused great interest. By increasing the Cl content in the mixed halogen components, the emission characteristics of PeNCs can be customized to the pure blue spectral region with high color purity. Therefore, doping Cl into perovskite structure is a direct method to achieve blue light emission. However, due to the low formation energy of chlorine vacancies, the addition of chlorine often generates a large number of Cl vacancies with trapped states in CsPb (Br/Cl) ∝ PeNCs. These defects lead to exciton trapping, structural instability, and severe luminescence quenching. In addition, the inherent ionic properties of perovskite make mixed halide PeNCs prone to unwanted ion migration, leading to phase separation and color instability in electroluminescent devices.

  Recently, metal ion doping has become a promising strategy for enhancing the stability of mixed halide blue perovskite while addressing issues related to lead toxicity. Many metal ions have been introduced into CsPb (Br/Cl) ∝ NCs to improve their stability. In addition to these metal ions, non-toxic In ³ ⁺ ions are located at the diagonal position of Pb in the periodic table, with a smaller ionic radius, and have attracted much attention for their potential applications in optoelectronic devices. Zhou et al. reported that doping with In ³ ⁺ ions improves the stability of red emitting CsPbBrxI ∝ - ₓ perovskite quantum dots by increasing the lattice formation energy. However, to our knowledge, In ³ ⁺ ions are rarely used in pure blue PeLEDs. Although the incorporation of various metal ions has shown promising prospects in improving stability, their effectiveness in reducing surface defects is limited, leaving behind residual halogen vacancies and uncoordinated Pb ² ⁺ ions. These surface defects can impair stability when exposed to external stresses such as heat, light, or electric fields. Therefore, reducing surface defects and enhancing the stability of pure blue CsPb (Br/Cl) ∝ NCs are crucial for improving their performance in PeLED applications. The use of zwitterionic molecules as passivators has become an effective strategy to improve the optoelectronic performance and stability of PeNCs. Specifically, sulfonated betaine (a bifunctional zwitterionic molecule) has been proven to be an effective ligand for passivating surface defects in PeNCs, significantly enhancing their optoelectronic properties and stability.

  Chen Guanying and others from Harbin Institute of Technology proposed a synthetic strategy for preparing CsPb (Br/Cl) ∝ NCs through sequential organic-inorganic hybrid modification. Firstly, the In ³ ⁺ cation is introduced into the NC lattice, followed by ligand post-treatment with the zwitterionic molecule 3- (decyldimethylammonium) propane-1-sulfonate. This dual modification strategy synergistically combines inorganic doping and organic passivation to enhance the performance of CsPb (Br/Cl) ∝ NCs. Theoretical calculations reveal that In ³ ⁺ doping increases the formation energy of PeNCs, while also increasing the formation energy of halogen vacancy defects. The bifunctional zwitterionic ligand SB3-10 effectively reduces surface defects and inhibits halide ion migration by coordinating with uncoordinated Pb ² ⁺ through its - S ═ O group. This combination strategy enhances crystallinity and minimizes phase separation during device operation, thereby improving the performance and stability of the resulting PeLEDs. It is worth noting that the prepared PeLEDs exhibit excellent spectral stability and achieve an impressive external quantum efficiency of 12.2%, highlighting the potential of this strategy in advancing high-performance pure blue PeLEDs.