Exploring the Influence of Grain Boundaries on Carrier Transport and PEC Activity of Hematite Photoelectrodes

In this study, highly oriented hematite photoelectrodes composed of single-crystal particles (SC-Fe 2 O 3 ) were prepared on FTO via the hydrothermal method, and the effects of grain boundaries on carrier transport and photoelectrochemical (PEC) performance were systematically investigated. By comparing the carrier mobility, conductivity, and PEC properties of hematite electrodes composed of single-crystal and polycrystalline particles, it was found that grain boundaries not only scatter carriers and enhance recombination, reducing the carrier diffusion length, but also form double Schottky barriers that weaken the modulation of the space charge layer by the applied potential, thereby hindering carrier transport. Experimental results showed that the carrier mobility and carrier concentration of the single-crystal particles were significantly higher than those of the polycrystalline electrode. Moreover, the electrode composed of single-crystal particles achieved a photocurrent density of 2 mA/cm 2 at 1.6 V (vs RHE) and an onset potential as negative as 0.6 V (vs RHE). Additionally, the bulk and interface carrier separation efficiencies of the SC-Fe 2 O 3 electrode reached as high as 34% and 90%, respectively, demonstrating an excellent PEC performance. This study provides important guidance for understanding the role of grain boundaries in photoelectrodes and optimizing carrier transport.