Investigating the Impacts of Surface Layers on the Durability of GaInP₂ Photocathodes for Photoelectrochemical Water-Splitting

Photoelectrochemical (PEC) water-splitting couples light-absorbing semiconductor materials with water-splitting electrocatalysts to directly produce hydrogen from solar energy. Systems with tandem III-V semiconductor absorbers (e.g. GaInP₂/GaAs) have demonstrated the highest solar-to-hydrogen (STH) conversion efficiencies to date.^1,2,3 A GaInP₂ top junction is common to many of the highest performing systems, and the incorporation of a thin AlInP₂ window layer to decrease surface recombination and a semiconductor capping layer to protect the window layer from corrosion has been shown to improve top cell performance.^1,4 However, the stability of III-V-based PEC devices remains limited, and durability is a major challenge in the field of PEC.<br/><br/>In this work, we investigate the impacts of a window layer and capping layer in conjunction with an MoS₂ catalytic layer on durability and performance in single-junction GaInP₂ photocathodes. GaInP₂ photocathodes with a window layer only and both a window layer and a capping layer were fabricated and compared to a baseline MoS₂/GaInP₂photocathode. PEC characteristics were probed via current-voltage, chronoamperometry, and integrated photon-to-current efficiency measurements under solar simulator illumination. Photocathode degradation was monitored by <i>in situ</i> optical microscopy and post-test XPS measurements, illustrating macroscopic degradation modes.<br/><br/>Overall, the photocathode with a capping layer and window layer gave both the best performance and longevity. This photocathode surface architecture can be translated to the top junction of other tandem absorber III-V systems to improve device stability and efficiency.<br/><br/>References:<br/>(1) Young, J. L.; Steiner, M. A.; Döscher, H.; France, R. M.; Turner, J. A.; Deutsch, T. G. Direct Solar-to-Hydrogen Conversion via Inverted Metamorphic Multi-Junction Semiconductor Architectures. <i>Nat. Energy</i> <b>2017</b>, <i>2</i>, 17028.<br/>(2) Khaselev, O.; Turner, J. A. A Monolithic Photovoltaic-Photoelectrochemical Device for Hydrogen Production via Water Splitting. <i>Science</i> <b>1998</b>, <i>280</i>, 425–427.<br/>(3) Cheng, W.-H.; Richter, M. H.; May, M. M.; Ohlmann, J.; Lackner, D.; Dimroth, F.; Hannappel, T.; Atwater, H. A.; Lewerenz, H.-J. Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency. <i>ACS Energy Lett.</i> <b>2018</b>, <i>3</i>, 1795–1800.<br/>(4) Steiner, M. A.; Barraugh, C. D.; Aldridge, C. W.; Alvarez, I. B.; Friedman, D. J.; Ekins-Daukes, N. J.; Deutsch, T. G.; Young, J. L. Photoelectrochemical Water Splitting Using Strain-Balanced Multiple Quantum Well Photovoltaic Cells. <i>Sustain. Energy Fuels</i> <b>2019</b>, <i>3</i>, 2837–2844, DOI: 10.1039/c9se00276f.