Improving Carrier Multiplication in Quantum Dots
The promise of capturing sunlight and converting it into electricity has many looking forward to a solar powered future, but there are some technological hurdles to overcome first. Among these is that higher-energy photons do not necessarily translate to greater electrical power. Researchers at Los Alamos National Laboratory however have discovered a way to address that issue for quantum dots.
Quantum dots are micro-scale semiconductor crystals that can be designed with special optical properties, making them a good fit for solar power. Their small size also enables carrier multiplication to occur, and increase the number of electrons one photon can excite, but it is not an easy process. First a high energy photon, such as blue and ultraviolet photons, strikes and excites one electron, making it 'hot' with energy. As the hot electron travels, it can collide with un-excited electrons, imparting enough energy to them to get them moving too. The problem is that before other electrons are excited, that first hot electron may just radiate the energy away as heat. By redesigning the nanostructures of the core and shell of a quantum dot though, the LANL researchers demonstrated a means to slow the cooling of the hot electrons, encouraging as much as a fourfold increase in carrier multiplication.
The research was done with lead selenide/cadium selenide quantum dots, but the basis for encouraging carrier multiplication by slowing cooling is general, so this work can be applied to other dots. It could also be improved by applying other means of increasing multicarrier yield, making dots even more effective at converting the energy of sunlight.
Source: Los Alamos National Laboratory