A Quantum Approach to Simulating Photoelectrochemical Cells

Photoelectrochemical (PEC) water splitting cells offer an environmentally friendly way to store solar energy in chemical form. However, increasing the efficiency of the current solutions requires detailed understanding of the physical processes on both sides of the solid-liquid interface. Accurate computational modeling offers information on the charge carrier dynamics of an operational cell, giving key insight required in developing new solutions.<br/>While the performance of simple PEC cells can be adequately explained with semi-classical drift-diffusion theory, the increasing interest towards thin film cells, multi-layered devices and nanostructures in general requires theoretical treatment that can capture the quantum phenomena in these nanoscale features. Cells using III-V materials often make use of thin film protective layers, highly doped contact regions and multi-junction designs where tunnelling and other quantum effects have a significant impact on the charge transport inside the electrode. The non-equilibrium Green’s function (NEGF) approach offers an excellent compromise between the limiting assumptions included in classical transport equations and computationally heavy <i>ab initio</i> quantum chemical simulations.<br/>We have implemented a numerical model of the semiconductor photoelectrode of a PEC cell based on the NEGF formalism, where The NEGF equations are solved self–consistently together with Poisson’s equation and electrochemical boundary conditions. The NEGF model allows us to compute an energy resolved solution of the charge carrier densities and corresponding currents inside the semiconductor electrode at nanoscale. The presented simulation offers important insight into the operation of PEC cells at nanoscale where quantum effects have a significant contribution to the charge transport, providing a pathway for designing more efficient and economically viable devices.<br/>Acknowledgement: This research was funded by Academy of Finland