Understanding Efficiency Limits of the Photoelectrochemical Devices
New analysis provides insight into factors that govern photoelectrochemical device performance .
Fountaine, K. T., Lewerenz, H. J. & Atwater, H. A. Efficiency limits for photoelectrochemical water-splitting. Nature Communications, DOI: 10.1038/ncomms13706 (2016).
Light absorption, charge carrier transport, and catalysis are the physical processes that govern the operation of photoelectrochemical (PEC) devices. Due to the complex and multicomponent nature of such devices, obtaining accurate limiting efficiencies for their performance has been challenging. The recent JCAP paper published in Nature Communications introduces a transcendent approach to understanding PEC device performance for arbitrary material and device quality, using five representative parameters: semiconductor absorption fraction, external radiative efficiency, series resistance, shunt resistance and catalytic exchange current density to account for imperfect light absorption, charge transport and catalysis.
Animation illustrates the compilation of the sensitivity analysis of the maximum photoelectrochemical efficiency to semiconductor external radiative efficiency; (a) Maximum efficiency vs. semiconductor external radiative efficiency (ERE) for a single junction photoelectrochemical device, with the color axis indicating the semiconductor bandgap (eV) that corresponds to the maximum efficiency; (b) Animation of efficiency vs. semiconductor bandgap with the external radiative efficiency evolving in time; red dot indicates the bandgap corresponding to the maximum efficiency at a given ERE value that is plotted on (a).
The authors first present the analytic equations and solutions for the limiting efficiencies of photoelectrochemical water-splitting devices based on the ultimate limits of device physics as well as two more realistic scenarios based on currently achievable material and device parameters. Subsequently, the article presents a parameter variation study centered around these ideal and realistic cases that demonstrates the varying impact of each phenomenon (light absorption, charge transport, catalysis) on overall device efficiency and efficiency limits. Finally, authors compare the reported experimental efficiencies from three water-splitting devices to their theoretical limit analysis results, illustrating the utility of their framework for identification of limiting factors in overall device performance.
This new analysis provides a framework through which one can understand previously reported PEC limiting efficiencies and provides insight into which factors must be optimized and controlled to improve PEC efficiency.
This work is performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy (Award No. DE-SC0004993).
Corresponding authors: Katherine.Fountaine@ngc.com