Device-scale modeling of valley photovoltaics

TL;DR

This paper introduces a novel device model for valley photovoltaics, incorporating valley scattering effects, and demonstrates that simply increasing electric fields does not enhance efficiency, challenging prior assumptions.

Contribution

It presents the first device-scale model for valley photovoltaics that includes electric-field-dependent valley scattering rates and analyzes their impact on device performance.

Findings

Valley scattering effects are critical in valley photovoltaic device behavior.

Increasing built-in electric fields does not necessarily improve efficiency.

The model explains why high efficiency is difficult to achieve in current devices.

Abstract

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 electric-field-dependent valley scattering rates extracted from previous ensemble Monte Carlo simulations. We show that the condition of nonequilibrium carrier populations in the satellite valleys is not enough for valley photovoltaics to achieve high efficiency. We also show that increasing the built-in electric field of the valley-scattering region does not improve efficiency, contrary to previous suggestion.