Device-scale modeling of valley photovoltaics

We present a Poisson/drift-diffusion model that includes valley scattering effects for simulating valley photovoltaic devices. The valley photovoltaic concept is a novel implementation of a hot-carrier solar cell and leverages the valley scattering effect under large electric field to potentially achieve high voltage and high efficiency. Fabricated devices have shown S-shaped current–voltage curves, low fill factor, and, thus, low efficiency. We hence develop the first device model for valley photovoltaics. Our model includes quasi-equilibrated carrier populations in the satellite valleys and electric-field-dependent valley scattering rates extracted from previous ensemble Monte Carlo simulations. We show that nonequilibrium carrier populations in the valleys are not enough for valley photovoltaics to achieve high efficiency. Within our model, we also show that increasing the built-in electric field in the valley-scattering region does not improve efficiency, contrary to previous suggestion. Since our model does not show high efficiencies, achieving high efficiency valley photovoltaics requires producing high carrier temperatures—in addition to the separated carrier populations included in our model—or architecture changes from the existing devices.