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Efficient use of light and electricity is an essential step towards a sustainable society. Optoelectronic devices such as photodetectors and solar cells are useful devices to obtain electric signals and energies from light. However, these light-to-current conversion processes cause thermal and radiative energy losses, which are serious problems of energy waste. Here, I study optoelectronic energy recycling in semiconductor nanostructures.

The strategy to realize optoelectronic energy recycling is to utilize a quantum cooperative effect in nanomaterials. In my recent studies, I have revealed ultrafast generation processes of electrons and holes in nanomaterials. In semiconductor nanomaterials with their sizes of several nanometers, photogenerated electrons and holes are strongly affected by the quantum confinement. Quantum-confined electrons and holes form unique quantum states called multiexcitons, which are hardly generated in bulk semiconductors. Since a multiexciton involves multiple electrons and holes, multiexcitons have a great potential to enhance electric signals in optoelectronic energy conversion. In order to boost photon-to-current conversion efficiencies via multiexcitons, my research focuses on electronic coupling between semiconductor nanostructures. I will establish a new energy recycling system in coupled nanostructures, where thermal and radiative energies are collected and recycled for optoelectronic energy conversion processes.