Metal oxide nanocrystals for light-driven energy storage

In a world struggling to face the disruptive consequences of global warming, developing new energy conversion and storage solutions is of fundamental importance. This PhD thesis focuses on emerging heterostructures based on Indium Tin Oxide nanocrystals (ITO NCs) and two-dimensional Transition Metal Dichalcogenides (2D TMDs) for innovative light-driven optoelectronic nanodevices and energy storage solutions, combining the harvesting, conversion and storage aspects into a unique hybrid nanomaterial. Doped Metal Oxide (MO) NCs are attracting growing interest as nano-supercapacitors due to their ability to store extra charges in their electronic structure with record-high values of capacitance. Remarkably, these materials can be charged with light (i.e., photodoping), a process at the core of this project and so far not understood electronically. Here, the fundamental features involved in the charge accumulation process are investigated and the physics of photodoping explained. Complete control over energetic band bending and depletion layer engineering is demonstrated, exposing the key role of electronically depleted layers in core-shell NCs. Light-induced depletion layer modulation and band bending is the main mechanism responsible for the storage of extra charges in doped MO supercapacitors. Moreover, multi-electron transfer reversible reactions were observed in photodoped NCs when exposed to a frequently used electron acceptor. The coupling between ITO NCs and 2D TMDs allowed the implementation of a novel all-optical localized charge injection scheme for the manipulation of unperturbed 2D materials. Hybrid 0D-2D heterostructures proved all-solid-state photodoping possible, with promising charging dynamics and capacitance values. Theoretical modeling tools were developed, leading to the optimization of the charge storage capacity of 0D NCs. This work is of particular interest for the fabrication of the next-generation of nanostructured light-driven supercapacitors.