Enhanced Charge Separation and Collection in High-Performance Electrodeposited Hematite Films

Hematite electrodes with variable morphologies were prepared via a simple electrodeposition (ED) method. The photoelectrochemical (PEC) properties of planar and nanostructured electrodes were examined under PEC water oxidation and compared to that of planar analogue prepared by atomic layer deposition (ALD). The water oxidation performance of electrodeposited planar thin films was comparable to the nanostructured films; surprisingly, both ED films significantly outperformed the ALD-made planar films. The superior performance is attributed to variations in the crystallographic properties which results in enhanced hole transport and collection, as confirmed by photoelectrochemical and electrochemical impedance spectroscopy measurements and structural analysis. These results indicate a nonzero hole diffusion length for the electrodeposited hematite thin films in contrast to the ALD counterparts. Electrodeposited hematite thin films modified with Co-Pi exhibit near-unity hole collection efficiencies and produce the highest photocurrent among reported planar electrodes. This approach thus provides a simple and scalable approach to prepare high-performance thin film absorber hematite electrodes for solar water splitting.