Energy transfer between quantum dots of different sizes for quantum dot solar cells

Exciton recombination and slow charge carrier transport, major limitations of advanced photovoltaic cells, may be mitigated by designing cells with strong electric fields in the active regions. This may be done by combining quantum dots (QDs) of different Fermi levels in close proximity. While previous reports of quantum dot solar cells utilizing QDs of different sizes indicate that electrons and holes are transferred together from large bandgap QDs to small bandgap quantum dots, lowering the efficiency of the solar cell, we report a mechanism that may be able to use different bandgap QDs to split excitons and drive charge carrier transport, increasing the efficiency of solar cells. Quantum simulations of band structures of QDs show indications of this behavior, and experiments on solar cells with quantum dots of different sizes separated by thin insulating layers show improved photocurrent compared to solar cells with QDs of the same size.