A Route Towards Efficient Energy Relaxation from Nanocrystals to Oxide-free Semiconductor Surfaces

University Of Texas At Dallas, Richardson TX

Investigators

Abstract

Abstract Technical: Energy-transfer-based hybrid nanostructures judiciously engineered from components with separate functionalities offer a versatile platform for optoelectronic device applications. Light absorption in the strongly absorbing component of the hybrid is followed by non-contact electromagnetic energy transfer from the resulting excitons in nanostructures to electron-hole pairs in the conductive semiconductor thin film. This electromagnetic manipulation of excitations in nanoscale materials with well-controlled interfaces is an important step towards the next generation of functional nanodevices, which does not rely on charge transfer between the components. This project focuses on the fundamental principles of radiative and non-radiative energy transfer phenomena between highly absorbing nanocrystal quantum dots (NQDs) and high-mobility Si semiconductor components combined in layered hybrid nanostructures. The first effort aims to study non-radiative energy transfer from monolayers of NQDs covalently grafted on Si surfaces. To facilitate complete light absorption, multilayer NQD structures are to be fabricated and energy 'funneling' diffusion via non-radiative interactions between nanocrystal layers into Si substrate is explored and optimized. The second task focuses on radiative coupling of nanocrystal emission to waveguiding modes in Si nanomembranes. Placed in the vicinity of a high dielectric constant material such as Si, the nanocrystal emission is converted to waveguide modes in the Si layer where it is eventually absorbed, contributing to overall energy transfer. The third direction explores the applicability of new multishell NQDs that possess long-lived multiexitonic states for energy transfer. The overall energy transfer efficiency of planar NQD/Si structures is assessed by employing time-resolved photoluminescence spectroscopy combined with photocurrent measurements. The results of this research will lead to the understanding of energy transfer pathways in hybrid excitonic structures that overcome charge trapping related to interfacial states. Together with modeling tools and guidelines for achieving desired functionalities, these results could be applied to engineer practical architectures for efficient photovoltaic structures. Non-technical: Nanostructures composed on nanoparticles attached to thin silicon films offer a versatile platform for modern photonics with applications in advanced sensing, photovoltaics and novel light emitting sources. The fundamental research results of this project are expected to significantly impact our understanding of energy transfer phenomena and manipulation in these nanostructures leading to more efficient optoelectronic devices of great benefit to society. Students participating in this research are able to acquire expertise in the field of excitonics and hybrid nanomaterials. The research is inherently interdisciplinary in nature, allowing students to gain proficiency in physics, photonics and materials science and to develop both experimental and modeling skills. A strong effort is devoted to involve undergraduate and pre-college students and facilitate their interest in science. The PI of this project is committed to knowledge transfer via enhancing the curriculum by developing a course on Photonics Applications for Sustainable Energy and the interaction with the local industry.