DEVELOPING EFFICIENT AND STABLE PEROVSKITE NANOCRYSTALS-BASED BLUE LIGHT EMITTERS

Abstract

Higher-resolution displays with improved color quality and wider coverage of the visible spectrum have become a need of the future. Technological advancements in recent decades have resulted in giant leap in display technology from erstwhile incandescent lamps to Cathode Ray Tubes (CRTs) followed by Liquid Crystal Display (LCD) and, finally Light Emitting Diodes (LEDs)[1]. The development of LEDs became industrially competitive with the emergence of Organic LEDs (OLEDs) as well as Quantum Dot LEDs (QLEDs). Although they provided much better display qualities when compared to their earlier counterparts, their inherent weaknesses limit attaining more efficient devices fabricated through them. For OLEDs, their high vacuum thermal evaporation processing technique renders large area processing ineffective, whereas their wide full width at half maxima (FWHM) restricts attaining full-color gamut[2]. Although displays built with QLEDs using II-VI and III-V group Quantum Dots (QDs) offered improved color purity and simpler solution processibility, the element Cadmium (Cd) in these materials fails to meet the European Union’s restriction of hazardous substances legislation requirement[3]. Similarly, even though Cd-free QDs, such as Indium Phosphide (InP), have wider emission linewidths and lower Quantum Efficiency (QE) than Cadmium Selenide (CdSe) QDs, they also face industrial difficulties of complex high-temperature synthesis and expensive raw precursor materials[4]. These persistent limitations and vulnerabilities resulted in a search for new materials that could enhance device efficiency to new levels hitherto unachieved. The discovery of perovskite materials possessing excellent photo-voltaic and electro-voltaic properties has led to their utilization in this area of technology. Recent progress in understanding their electronic structure and better assessment of their charge carrier dynamics have now put them at the forefront for use as emissive layers in the display industry[5]. Due to their high Electroluminescence Quantum Yield (ELQY) - spectral tunability, high color purity, and easy colloidal synthesis that yield materials with low defects, lead halide perovskite semiconductors have emerged as a promising material for LEDs[6]. This study aims at developing efficient and stable Cesium Lead Halide Perovskite nanocrystals (NCs) for blue light emitters. In this study, longer wavelength Cesium Lead Bromide-based perovskite NCs are converted to shorter wavelength blue Cesium Lead Bromide/ Chloride NCs using an anion exchange method[7]. Their environmental stability and Photoluminescence (PL) characteristics were studied, and the effect of mixing Zinc Oxide (ZnO) NCs to enhance the stability by passivation of traps (defect states) of these perovskite NCs was carried out. Finally, detailed characterization of these NCs using available instruments like Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Ultraviolet-Visible (UV-vis) Spectrometer, Fluorescence Lifetime Spectrometer (FLS), and Photoluminescence (PL) Spectrometer was conducted. In the end, a blue Light-emitting Diode (LED) was fabricated using these perovskite NCs.