Development of Chalcogenide Thin Film Materials for Photoelectrochemical Hydrogen Production
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Development of Chalcogenide Thin Film Materials for Photoelectrochemical Hydrogen Production Nicolas Gaillard, Dixit Prasher, Jess Kaneshiro, Stewart Mallory and Marina Chong Hawaii Natural Energy Institute, University of Hawaii at Manoa, Honolulu, HI 96822, USA ABSTRACT In the present communication, we report our efforts to integrate chalcogenide-based photoelectrochemical (PEC) materials into a standalone device capable of water-splitting using sunlight as the only source of energy. More specifically, the PEC performances of copper gallium diselenide are presented. First, a brief introduction to the material microstructural characteristics is presented. Then, the PEC properties are discussed, including incident-photonto-current efficiency (>60% in the visible), Faradaic efficiency (uncatalyzed, 86%) and durability (400 hours). Finally, we report the solar-to-hydrogen benchmark efficiency (3.7%) of a device made of a CuGaSe2 photocathode and a-Si solar cells measured in a 2-electrode configuration using a RuO2 counter electrode. INTRODUCTION Photoelectrochemistry (PEC) is considered one of the most efficient methods to produce alternative fuels. The efficiency, cost and durability of lab-scale systems, however, are insufficient to allow this technology to become economically feasible1. The chalcogenide materials are exceptionally good candidates to meet the requirements identified for efficient, cheap and sustainable solar fuel (such as hydrogen) production. There are five key points that make chalcogenides an ideal class for PEC applications. First, exceptional photo-conversion efficiency, as observed for high-performance 1.18 eV CuInGaSe2 solar cells, allows the generation of tremendous amounts of photocurrent density, up to 35 mA.cm-2 at saturation2. The, subsequent cost-effective deposition processes used to make PEC materials have been already developed by the PV industry. As well, the chalcogenide material class is known to be highly tolerant to structural defects, allowing the use of even cheaper deposition processes, such as inkbased methods3. It is also important to note that the chalcogenide material class allows for element substitution with cheaper materials such as zinc or tin which may replace indium and gallium4. Finally, since chalcogenides are bandgap-tunable, it is possible to adapt the optical characteristics of the PEC top layer to maximize light transmission and consequently power underlying PV cells in a hybrid photoelectrode (HPE) configuration5. In the present communication, we report specifically on the performances of chalcopyrite (CuInGaSe2) materials. First, we present the basic microstructural characteristics of this class. The PEC properties measured in a 3-electrode configuration are reported. Then, we discuss our current strategy to incorporate this class into a standalone PEC system and report its benchmark solar-to-hydrogen (STH) efficiency. Finally, we conclude on these results and briefly discuss possible alternatives to further increase the optical bandgaps of the chalcopyrites
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