Synthesis of high-quality blue-emitting perovskite NCs through defect passivation

다국어 초록 (Multilingual Abstract)

Perovskite nanocrystals (NCs) have garnered significant attention as promising emissive layers for light-emitting diodes (LEDs) due to their high photoluminescence quantum yield (PL QY), narrow full-width at half-maximum (FWHM), facile tunability of emission colors, defect tolerance, and rapid advancements in external quantum efficiency (EQE) for green and red emitters. However, blue-emitting perovskite NCs have shown relatively slow progress, with EQEs remaining below 10%. In devices, mixed halide (Cl/Br) perovskite NCs offer facile tunability of emission wavelengths from deep blue (450 nm) to sky blue (490 nm) by adjusting the Cl/Br composition. Nevertheless, their low efficiency and limited operational stability, including challenges such as phase segregation, remain critical issues to address. Moreover, vacancies in perovskites are the predominant defects. While defect-tolerant compositions like CsPbBr3 and CsPbI3 result in relatively shallow trap states, CsPbCl3 introduces deeper trap states within the bandgap. These deep trap states irreversibly capture charge carriers, leading to non-radiative recombination and undermining the device performance. Therefore, passivating vacancies in blue-emitting perovskite NCs is crucial to improving their efficiency and stability. In this study, we present a simple yet innovative in-situ method to synthesize high-quality blue-emitting perovskite NCs with mixed halide compositions (Cl and Br) by merely extending the reaction time. This straightforward and highly effective parameter has often been overlooked in perovskite NC synthesis. Traditional methods for synthesizing blue-emitting CsPbBrxCl3-x NCs using PbCl2 and PbBr2 faced challenges with prolonged reaction time. However, we found that introducing impurity metal halides, such as ZnBr2 instead of PbBr2, allowed for the synthesis of CsPbBrxCl3-x NCs with reaction time exceeding 90 min. These NCs demonstrated significantly enhanced PL QY, along with superior air and thermal stability compared to conventional samples. Our analysis revealed that the improved optical properties resulted from effective passivation of halide vacancies during the extended reaction period. Moreover, LEDs fabricated using these blue-emitting NCs without any post-treatment showed significantly reduced phase segregation, even under high operating voltages, thanks to the effective halide vacancy passivation.

목차 (Table of Contents)

• Table of Contents. i
• List of Figures ii
• List of Tables vi
• Abstract v
• 1. Introduction 1
• 2. Materials and methods 4
• 3. Results and Discussion 7
• 5. Reference 22
• 국문요지 25