Nonequilibrium Green's function simulation of Cu2 O photocathodes for photoelectrochemical hydrogen production

In this work we present a simulation of the semiconductor electrodes of photoelectrochemical (PEC) water-splitting cells based on the nonequilibrium Green's function (NEGF) formalism. While the performance of simple PEC cells can be adequately explained with semiclassical drift-diffusion theory, the increasing interest towards thin-film cells and nanostructures, in general, requires theoretical treatment that can capture the quantum phenomena influencing the charge carrier dynamics in these devices. Specifically, we study a p-type Cu2O electrode and examine the influence of the bias voltage, reaction kinetics, and the thickness of the Cu2O layer on the generated photocurrent. The NEGF equations are solved in a self-consistent manner with the electrostatic potential from Poisson's equation, sunlight-induced photon scattering and the chemical overpotential required to drive the water-splitting reaction. We show that the NEGF simulation accurately reproduces experimental results from both voltammetry and impedance spectroscopy measurements, while providing an energy-resolved solution of the charge carrier densities and corresponding currents inside the semiconductor electrode at nanoscale.