Understanding Multiple Exciton Generation and Charge Extraction in All-Inorganic Nanostructured Solar Cells from first principles

• Applicant: Dr. Stefan Martin Wippermann
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2012 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 211374683

This proposal investigates a transformative new paradigm of solar energy conversion:1. a high efficiency Multiple Exciton Generation (MEG) pathway2. the corresponding challenge of charge extraction3. in all-inorganic nanostructured solar cellsMEG was recently observed in nanoparticles (NPs) and is not subject to the 31% theoretical solar energy conversion limit. It is planned to utilize density functional theory based methods to explore systematically the MEG and charge extraction processes in Si and Ge NP-based all-inorganic solar cells, with focus on the NP surfaces and charge transport. The applicant wants to answer the following questions related to:1. Competing MEG theoriesAt present there are three competing theories to account for the MEG being enhanced so much over its small bulk value. Which is the correct one? Calculating the NP spectra including exciton-exciton interaction within the three different frameworks will allow a comparison with experimental studies, in an attempt to identify the ultimately correct theory of MEG.2. NP surface effectsHow do NP surface reconstruction and passivation influence the electronicstructure and spectra of the NPs? How does it influence the charge transport? How should the surface passivation be chosen to optimize the competing design requirements of preserving quantum confinement in support of the MEG process, while still ensuring a strong enough coupling for charge extraction?3. NP-NP couplingIn realistic solar cell architectures the NPs are relatively close to each other. Towhat extent does the electronic coupling between NPs influence their spectra? How does the NP-NP separation influence the charge extraction?Ideally, this project will not only lead to a thorough understanding of the MEG process in nanoparticles, but should allow for qualitative predictions about how to optimize the efficiency of both the MEG and charge extraction processes in realistic solar cell applications.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professorin Giulia Galli, Ph.D.