Hybrid organic/metal-oxide shells on semiconductor nanocrystals via colloidal atomic layer deposition

The escalating energy demand and the imperative necessity to reduce the carbon footprint require transformative approaches to energy conversion. Materials chemistry plays a pivotal role in addressing these global challenges by developing novel materials for cleaner, more efficient, and sustainable technologies. Colloidal semiconductor nanocrystals, amongst which quantum dots (QDs), have emerged as versatile building blocks for energy mediation.QDs exhibit intrinsic properties that make them unique platforms to investigate and to provide solutions for different energy conversion processes. In particular, their ability to interact with light enables their use in photovoltaics (converting photons into electricity), photon manipulation (up- and down-conversion), and photon-to-chemical bond conversion in photocatalysis. However, challenges persist towards their implementation, including ensuring chemical and colloidal stability for prolonged device lifetimes and advancing QD-based photocatalysis. Furthermore, more efforts towards exploring alternative QD compositions are needed to address environmental and toxicity concerns.This thesis focuses on further developing and understanding a colloidal atomic layer deposition (c-ALD) method for depositing metal-oxide matrices on QDs while preserving their colloidal stability.The first two experimental chapters focus on the nucleation mechanisms of metal-oxide coatings by c-ALD. Chapter 3 discusses the role of the native ligands during the nucleation using CdSe QDs and alumina as model system and reveals that the nature of the coating is in fact a hybrid metal-oxide/ligand structure. This insight is utilized in Chapter 4, where c-ALD is used as a surface treatment wherein a sub-nanometer thin metal-oxide shell enhances the stability of the QDs by hindering the ligand dynamicity. Additionally, the impact of the initial surface chemistry of the QDs on the growth of the metal-oxide coatings is investigated by assessing QDs with two different compositions, namely CdSe and PbS.Chapter 5 focuses on the development of CdSe@AlOx/chromophore heterostructures for triplet energy transfer, oriented to the application of photocatalysis of organic transformations. A novel c-ALD chemistry enables the growth of an interfacial single metal-oxide layer that offers more binding sites for the chromophore ligands compared to traditional mass driven exchanges. This chapter elucidates the challenges and opportunities in employing QDs for efficient energy transfer processes.Finally, Chapter 6 extends the c-ALD method to InP QDs, which results in optical and chemical stability enhancements. Insight into the surface chemistry of InP QDs are gained along with its impact on the nucleation of metal-oxide precursors. Concluding with insights and future prospects in Chapter 7, this thesis underscores the significance of surface chemistry in QD applications and highlights the potential of c-ALD for advancing energy conversion technologies.