Defect‐Cluster‐Boosted Solar Photoelectrochemical Water Splitting by n‐Cu2O Thin Films Prepared Through Anisotropic Crystal Growth

• Published in: ChemSusChem 2019-11, Vol.12 (21), p.4859-4865
• Main Authors: Chen, Ying‐Chu, Chen, Yen‐Ju, Popescu, Radian, Dong, Pin‐Han, Gerthsen, Dagmar, Hsu, Yu‐Kuei
• Format: Article
• Language: English
• Subjects: Anisotropy; Antisite defects; Coated electrodes; copper; Copper oxides; Crystal defects; Crystal growth; Crystals; defects; Glass substrates; Heat treatment; Lattice vacancies; Morphology; Photoelectric effect; Photoelectric emission; photoelectrochemistry; Photoluminescence; Silver chloride; Spectroscopy; Spectrum analysis; Thin films; Tin oxides; Water splitting
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201901798

Anisotropic growth of Cu2O crystals deposited on an indium‐doped tin oxide‐coated glass substrate through facile electrodeposition and low‐temperature calcination results in favorable solar photoelectrochemical water splitting. XRD, TEM, and SEM reveal that appreciable oxygen vacancies are populated in the Cu2O crystals with a highly branched dendritic thin film morphology, which are further substituted by Cu atoms to form Cu antisite defects exclusively along the [111] direction. The post‐thermal treatment presumably accelerates such migration of the lattice imperfections, favoring the exposure of the catalytically active (111) facets. The Cu2O thin film derived in this way shows n‐type conduction with a donor concentration in the order of 1017 cm−3 and a flat‐band potential of −1.19 V vs. Ag/AgCl, which is also confirmed by Mott–Schottky analysis. The material is employed as a photoanode and delivers a photocurrent density of 2.2 mA cm−2 at a potential of 0.3 V vs. Ag/AgCl, surpassing reported values more than twofold. Such superiority mostly originates from the synergism of the selective facet exposure within the Cu2O crystals, which have decent crystallinity, as shown by Raman and photoluminescence spectroscopy, and a favorable bandgap of 2.1 eV, as confirmed by UV/Vis spectroscopy. The n‐type Cu2O thin film reported herein holds excellent promise for solar‐related applications. Good defects! Oxygen vacancies are introduced in n‐type Cu2O thin films grown in oxygen‐poor conditions. Subsequent low‐temperature calcination triggers the clustering of those point defects, preferentially giving rise to (111) facets. Such crystallographic anisotropy stimulates a n‐Cu2O thin film photoanode to deliver a photocurrent density of 2.2 mA cm−2 for solar water splitting.