Zemin Zhang, Jason K. Cooper
Artificial photosynthesis, which converts carbon dioxide and water to valuable chemical fuels by storage of solar energy in chemical bonds, is an approach to respond the growing global energy demand while combating climate change. Photocathodes made from p-type semiconductors supply photogenerated electrons and catalytically active sites. An ideal p-type material should meet the requirements of: ideal bandgap, correctly aligned band energetics, good photovoltage, and excellent stability. The search for promising new materials has uncovered cooper-based ternary oxides as potential candidates. Among these materials, CuBi2O4, has been demonstrated with a low bandgap, suitable conduction band minimum, good stability, and a large photovoltage around 1 V. However, the practical performance is only several percent of the theoretical maximum. The path to realizing efficiency improvements begins with a fundamental understanding of the electronic structure and optical properties. Herein, we investigate the optoelectronic properties of p-type copper bismuth oxide through the synergy of DFT modeling and a variety of experimental characterization methods including for example: x-ray spectroscopy, time-resolved optical spectroscopy, photothermal deflection spectroscopy, and ellipsometry. In this talk, we will discuss the orbital character of the valance and conduction bands, the related electronic transitions making up the optical absorption, photocarrier dynamics, defects both in bulk and surface, and the limited diffusion length. The unification of the variety of characterization techniques provides a complete view of the material optoelectronic structure enabling a deeper understanding of its emergent properties. Informed by the electronic structure, we will discuss opportunities to improve performance limitations by structural modification.