Combined photoluminescence and electrical characterization of valley photovoltaic devices explained with an equivalent circuit
We present an equivalent-circuit analysis that simultaneously considers the photoluminescence and electrical responses of valley photovoltaic devices. Valley photovoltaics (VPV) are a novel concept for hot-carrier solar cells, where intervalley scattering of electrons in the absorbing material helps maintain the conduction-band electron populations at metastable satellite valleys, which are at energies higher than the conduction-band minimum. We measure intensity- and voltage-dependent photoluminescence and electrical signals of a VPV device, which has previously shown S-shaped current-voltage characteristics and thus low efficiency. We present an equivalent circuit that captures the S-shaped current-voltage curves and simultaneously describes our photoluminescence and electric measurements. The equivalent-circuit model indicates that a reverse diode causes inefficient extraction of electrons and thus the S shape. We use a Poisson/drift-diffusion model to demonstrate that the reverse diode can be either explained by the valley-scattering process itself or a heterojunction barrier. The reverse diode must be eliminated before VPV devices can achieve high efficiency.