Novel Iodine Source Strategy for Red Mixed Halide Perovskite Quantum Dots and Enhanced LED Efficiency

Perovskite nanocrystals (PeNCs) are highly promising materials for next-generation display technologies due to their outstanding optical properties, including high photoluminescence quantum yields, narrow emission linewidths, and tunable emission wavelengths. However, persistent challenges such as surface defects and halide vacancies, particularly during the purification process after synthesis, hinder the efficiency and stability of PeNC-based devices. These defects often degrade device performance, making it difficult to achieve both high efficiency and long-term stability in optoelectronic applications.<br/><br/>A key advantage of PeNCs is their ability to modulate emission wavelengths by adjusting the halide composition, as halide anions can be easily exchanged within the perovskite lattice. This anion exchange not only enables precise wavelength tuning but also helps mitigate defects by replenishing missing or deficient anions on the surface or within the crystal structure.<br/><br/>To further exploit these advantages, we developed a novel anion exchange precursor based on a mixture of trimethylsilyl iodide (TMSI) and tri-n-octylphosphine (TOP). 31P NMR spectroscopy confirmed the formation of a phosphonium iodide complex containing silicon, and we proposed a reaction mechanism in which phosphonium ions are generated through the interaction of TMSI and TOP. This precursor was applied to green-emitting PeNCs, successfully inducing anion exchange to produce red-emitting PeNCs with a high quantum yield of 90%.<br/><br/>In addition, we conducted a comparative analysis using various anion exchange precursors to evaluate their effects on the PeNC surface, employing a range of analytical techniques. The red-emitting PeNCs synthesized with the TMSI-TOP precursor were integrated into electroluminescent (EL) devices, achieving an impressive external quantum efficiency (EQE) of 21.69% and demonstrating high operational stability, maintaining stable performance for approximately 16 hours at a luminance of 100 Cd/m².<br/><br/>This study highlights the potential of TMSI-TOP as a highly effective anion exchange precursor, providing a pathway to high-efficiency, stable PeNC-based devices by addressing critical issues related to defect passivation and halide management.