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Excitonic Effects in Emerging Photovoltaic Materials: A Case Study in Cu2O

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journal contribution
posted on 19.01.2017, 00:00 by Stefan T. Omelchenko, Yulia Tolstova, Harry A. Atwater, Nathan S. Lewis
Excitonic effects account for a fundamental photoconversion and charge transport mechanism in Cu2O; hence, the universally adopted “free carrier” model substantially underestimates the photovoltaic efficiency for such devices. The quasi-equilibrium branching ratio between excitons and free carriers in Cu2O indicates that up to 28% of photogenerated carriers during photovoltaic operation are excitons. These large exciton densities were directly observed in photoluminescence and spectral response measurements. The results of a device physics simulation using a model that includes excitonic effects agree well with experimentally measured current–voltage characteristics of Cu2O-based photovoltaics. In the case of Cu2O, the free carrier model underestimates the efficiency of a Cu2O solar cell by as much as 1.9 absolute percent at room temperature.