Every time a solar cell absorbs sunlight or an LED emits light, a tiny paired particle called an exciton forms inside the semiconductor material—and how that exciton breaks apart or transfers energy determines the device’s efficiency. Current computer models can predict how excitons form, but they cannot yet simulate what happens when excitons collide with other particles, such as phonons or charge carriers. This project will develop new theoretical methods and computer code to fill that gap. The researchers will build tools that calculate, from fundamental quantum mechanics, how temperature affects exciton lifetimes and how excitons interact with lattice vibrations (polarons). They will test these methods on real materials, from 3D crystals to atom-thin 2D semiconductors. If successful, the work will give materials scientists a predictive capability they currently lack—allowing them to design better solar cells, LEDs, and optoelectronic devices by simulating exciton behaviour before building a prototype. This is fundamental science: the immediate output is a set of open-source computational tools and a unified theory of exciton scattering, not a commercial product. But similar first-principles methods have already transformed how industry designs batteries and catalysts.
View original technical description
In semiconductors and insulators, absorption of light generates correlated electron-hole pairs which are bound via the Coulomb interaction, forming quasiparticles called "excitons". Excitons are ubiquitous in semiconductors and insulators and are key players in standard optoelectronic devices. Excitons have a finite lifetime because they can dissociate upon scattering with other quasiparticles into constituent carriers, generating a photocurrent (useful for solar cells). They can also recombine and generate photons (e.g. in an LED) or transition into a different state upon transfer of energy or momentum (transport information in the form of energy). The underlying physics of how excitons form and interact with other quasiparticles is rigorously described within the quantum-mechanical theory of many-body interactions, and existing first principles techniques are generally formulated within the framework of many-body perturbation theory (MBPT). While this framework is technically challenging to apply to realistic materials from first principles, MBPT-based techniques developed to date constitute an extremely powerful set of theoretical and computational tools used to predict and understand the atomistic origins of excitonic properties in technologically relevant materials. However, formal theoretical frameworks and computational implementations capable of capturing the interaction of excitons with other quasiparticles are still in their infancy, thereby leaving a significant gap in the predictive power of these first principles techniques. This is therefore a tremendous opportunity to use our ample expertise and prior achievements to develop new first principles methods and frameworks that will allow us to accurately describe complex excited state physics in novel materials and significantly advance the predictive capabilities of ab initio computational materials modelling. The principal objectives of this project are as follows. We will 1) implement new first principles methods (beyond 1st order perturbation theory) for computing temperature dependent exciton binding energies and dissociation lifetimes within the BerkeleyGW computational package; 2) develop and implement new theory to understand exciton-polaron interactions; 3) apply computational and theoretical developments to different materials systems including 3D and 2D semiconductors, with binary, ternary and quaternary chemical composition and 4) develop a unified theory of exciton scattering with different quasiparticles, building upon the outputs of objectives 1-3 of this program.
Plain English summaries and category classifications on this site are generated by AI and may not perfectly reflect the original research.
Is something wrong? Let us know