DeXCTer

Over the last ten years, the development of two-dimensional (2D) semiconductor materials for new functional optoelectronic devices has been greatly stimulated by the outbreak of ultrathin nanostructures with thickness controlled at the atomic level. Among them, colloidal nanoplatelets (NPLs) of metal chalcogenides, with their large absorption cross section and high photoluminescence quantum yield, have shown their high potential for light-emitting applications such as LEDs and lasers. Electronic coupling between quantum wells, notably through the development of heterostructures, is now the next challenge to rise for applications based on light-to-electricity conversion. Indeed, the high exciton binding energy in these nanostructures inherently limits the exciton dissociation into free carriers, which is one of the main obstacles to efficient solar cells and photodetectors. So far, the coupling between vertically (cofacial)-stacked NPLs and within in-plane (edge-to-edge) hetero-NPLs has been limited and strongly suffers from the poor quality control of the interface. Here we propose to combine original synthesis methods and advanced optical spectroscopies in order to study charge transfer (CT) excitons in 2D NPL heterostructures with both in-plane and out-of-plane geometry and type-II alignment. In particular, we aim to investigate the effect of exciton wavefunction delocalization and CT character in the dynamics of charge transfer at the interface and of the following exciton dissociation using ultrafast time-resolved spectroscopy. The development of such 2D hetero-NPLs will be driven by deep structural characterizations using in particular Raman spectroscopy, targeting the interface quality and mechanical properties linked with the CT character of the exciton. Ultimately, we will engineer CT excitons with optical properties and lifetime controlled with external electric fields, by tuning the energy level offset and the relative electron-hole wavefunction overlap.