Novel Methods and Materials for Light-emitting Sources

Quantum dots have emerged as an avant-gardist element that finds application in a plethora of optoelectronic applications such as displays, solar cells, photodetectors, and lasers. Light-emitting diodes (LEDs) based on quantum dots (QDs) demonstrate high efficiency, a highly sought-after property in consumer electronics products. The unique optical and electronic properties of colloidal QDs stem from the quantum confinement effect. In fact, their composition is not the sole determinant of its characteristics as the size and shape of the QD allows for tuning the optoelectronic properties. QD light-emitting diodes (QD-LEDs) harness the desirable emissive properties of such nanomaterials to generate electroluminescence. The present study investigates the optical and electronic properties of various colloidal QDs to design innovative QD-LEDs. Perovskite cesium lead bromide (CsPbBr3) QDs are noteworthy for their high photoluminescence efficiency and narrow spectral emission. Nevertheless, perovskite QDs suffer from low stability as their respective devices. As a result, extensive efforts have been spent to improve the stability of perovskite QDs and a critical aspect is their purification, which requires careful attention in using anti-solvents that may irreversibly damage the nanomaterial. Moreover, if not removed, the excess of organic ligands can lead to an unsuitable (low-efficiency) film due to the lack of close packing of the QDs. My investigation aimed to enhance the external quantum efficiency (EQE) of CsPbBr3 QD-LEDs by developing a dedicated purification procedure combined with an improved device architecture. Systematic evaluation of various hole transport materials and device configurations reveals their impact on QD-LEDs performance, providing insights into the intricate interplay of energy level alignment and carrier mobility for improving EQE. Recent findings on near-infrared (NIR) QD-LEDs are shown in the second part of this study. To date, the best-performing QDs in LEDs operating in the NIR range are based on lead and mercury. In fact, there is a need for more efficient, heavy-metal-free compounds (and respective devices) for such light-sources. Heavy-metal compounds cannot obtain approval for commercial use due to the European Union's "Restriction of Hazardous Substances" directive. In this direction, colloidal InAs QDs are a promising candidate for NIR-QD-LED due to their low toxicity and recent material synthesis advancements. My study focused on material and LED engineering covering the NIR spectrum here.