First-Principles Simulations of Stability, Optical and Electronic Properties of Competing Phases in Chalcopyrite-Based Photoelectrodes

Abstract

Photoelectrochemical (PEC) hydrogen production is one promising approach to economically generating renewable fuels, yet the widescale deployment of leading photoelectrodes (e.g. GaInP-based devices) has been hampered by issues with durability, efficiency and cost. Chalcopyrite-based tandem photoelectrodes are attractive alternatives in that they offer a great flexibility in the choice of component materials necessary that drive the reactions for different device designs, offering ways to reduce the cost and to improve the performance. The synthesis of low-band gap chalcopyrites like CuInSe2 and alloys with CuGaSe2 (CIGSe) are known to exhibit a variety of Cu-poor phases (ordered-vacancy compounds or OVCs) that can greatly influence the resulting properties of fabricated devices, while the existence and properties of these phases in wider-band gap chalcopyrite compounds and alloys remains largely unexplored. Using hybrid functional calculations, we discuss the stability, optical and electrical properties of OVCs in a number of other chalcopyrite chemistries beyond CIGSe. We discuss the influence of such phases on the resulting absorption and band offsets that would result upon their formation, which have implications in device design. We additionally discuss experimental fingerprints that could be used to identify the existence of such phases in synthesized material. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the HydroGEN Consortium within the Department of Energy Office of Energy Efficiency & Renewable Energy (EERE) and Fuel Cell Technologies Office.