In the pursuit of efficient solar-to-fuel systems, semiconducting transition metal oxides (TMOs) have been extensively investigated as photoelectrode materials. While these materials can be composed of Earth abundant elements and exhibit desirable stability under reaction conditions, photocurrents obtained from TMO photoelectrodes tend to be significantly lower than the thermodynamic limits based on their bandgaps. In this work, two Cu-based semiconductors are chosen as representative platforms for understanding carrier relaxation pathways and their impacts on efficient photoelectrochemical (PEC) conversion: n-type Cu3V2O8 as a photoanode and p-type CuFeO2 as a photocathode. Despite of their favorable bandgaps (~ 2.5 and 1.5 eV for Cu3V2O8 and CuFeO2, respectively), both materials are characterized by poor charge extraction. The short minority carrier diffusion length is found to be a major limiting factor in both materials, as has been reported on other oxides such as Fe2O3. Transient absorption spectroscopy reveals that ultrafast trapping process cause short free carrier lifetimes (&lt; 500 fs), which explains why most of the photo-excited carriers are unable to reach the semiconductor-electrolyte junction. In parallel, the complicated band structures of two ternary metal oxides are resolved by means of ellipsometry and X-ray spectroscopy. By combining knowledge of electronic structure, carrier relaxation dynamics, and PEC performance, this research provides insights into current limitations of these newly-discovered light absorbers and informs strategies to overcome them.

Understanding optical properties and photocarrier dynamics in emerging copper-based photoelectrodes

253rd National Meeting (2017)

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