Illuminating the Origins of Ferroelectric‐Induced Photocurrent and Hole Lifetime Enhancement in BaTiO3 Photoanodes

Abstract Ferroelectric semiconductors can exhibit extraordinarily long charge carrier lifetimes following photoexcitation. However, it remains unclear whether these long‐lived charge carriers are available to participate in the necessary solar water splitting redox reactions. Presented here are coupled transient optical and photoelectrochemical measurements that demonstrate the correlation between photo‐generated hole lifetimes, photocurrent density, and the energetic driving force associated with enhanced performance in ferroelectric BaTiO 3 porous photoanodes with induced polarization states. For the first time, a three‐fold increase in photocurrent density following water‐oxidation‐preferential poling is correlated with a three orders of magnitude increase in hole lifetime in comparison to an un‐poled film. Transient absorption and photocurrent measurements demonstrate the polarized films benefit from reduced charge carrier recombination, enhanced charge carrier separation, increased hole population, and more efficient electron extraction over the water oxidation relevant timescales of µs to tens of seconds. Photoelectron spectroscopy and Kelvin probe measurements elucidate the effect of the presence and polarity of a ferroelectric polarization on core and band‐edge positions and work function values, ultimately revealing energy level differences of 300–400 meV that are found to be the driving force behind the associated lifetime and photocurrent gain.