Nanocrystals Physics, Engineering, and Future Energy Solutions

Supplies of clean energy are closely linked with global economic growth, social stability and quality of life. Developing energy-efficient devices and harnessing renewable energy (e.g., solar energy) are two solutions to meet this challenge. Nanocrystals could play an important role in these future energy solutions since the emergence of new fundamental physical properties on the nanometer scale could lead to much more efficient technologies for energy utilization and conversion. I will discuss two areas of my research based on nanocrystals: (1) Nanocrystals based photovoltaic and solid-state lighting devices. The easily size-tunable energy gap of nanocrystals makes them ideal photon-absorbing materials for solar-electricity devices. High quantum yield makes them a good candidate material for solid-state lighting. However, there are still challenging topics in this field, such as control of exciton dissociation or formation in a nanocrystal, control of charge transfer etc. I will discuss some results about nanocrystal surface modification and energy level alignments for nanocrystals-based optoelectronic devices, which are closely related to the topics aforementioned. (2) Interface electronic structures and charge dynamics of nanocrystals. Since the interface-to-volume ratio of a nanocrystal increases dramatically, the interface plays a critical role on material properties. It greatly affects charge carrier generation, transportation, and relaxation. Yet the microscopic nature, electronic structure and relaxation dynamics of these interface states are still poorly known, in part because of the lack of effective experimental probes of these nano-interfaces. In my recent research, I developed optical second harmonic generation and electrogenerated chemiluminescence spectroscopy to probe the interface electronic structure and carrier relaxation dynamics of nano-interfaces. Combined with photoluminescence measurements, we can obtain a more complete picture of the electronic structure of a nanocrystal. I will also discuss my future research plans, including development of nanomaterials for solar cells, and development of experimental methods to probe nanoscale charge-transfer.