Double superexchange in quantum dot mesomaterials

Abstract

A new optoelectronic mesomaterial is proposed in which a network of quantum dots is covalently connected via organic molecules. Optically generated excitons are rapidly dissociated with electrons subsequently hopping from dot to dot while holes transit via the connecting moieties. The molecules serve as efficient mediators for electron superexchange between the dots, while the dots themselves play the complementary role for hole transport between molecules. The network thus exhibits a double superexchange. In addition to enhancing carrier hopping rates, double superexchange plays a central role in mediating efficient polaron dissociation. Photoluminescence, dissociation, and transport dynamics are quantified from first-principles for a model system composed of small silicon quantum dots connected by organic moieties. The results demonstrate that double superexchange can be practically employed to significantly improve charge generation and transport. These are currently viewed as the critical obstacles to dramatic enhancements in the energy conversion efficiency of photovoltaic cells based on quantum dots.