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The performance of energy materials hinges on the presence of structural defects and heterogeneity over different length scales. Here we map the correlation between morphological and functional heterogeneity in bismuth vanadate, a promising metal oxide photoanode for photoelectrochemical water splitting, by photoconductive atomic force microscopy. We demonstrate that contrast in mapping electrical conductance depends on charge transport limitations, and on the contact at the sample/probe interface. Using temperature and illumination intensity-dependent current-voltage spectroscopy, we find that the transport mechanism in bismuth vanadate can be attributed to space charge-limited current in the presence of trap states. We observe no additional recombination sites at grain boundaries, which indicates high defect tolerance in bismuth vanadate. These findings support the fabrication of highly efficient bismuth vanadate nanostructures and provide insights into how local functionality affects the macroscopic performance.

Ubiquitous moisture in synthetic conditions and ambient environments can strongly influence the conductivity of ZnO semiconductors via the chemisorption and physisorption of water molecules on the ZnO surface. Such an intrinsically water‐sensitive nature will become more evident in mesoporous ZnO films where a large surface area and active sites are created simultaneously. However, fundamental insights underlying water‐mediated ZnO surface chemistry and electrical conductivity and the factors affecting them remain ambiguous due to the complexity of ZnO surfaces and the difficulties of in situ characterizations at multi‐dimensions. Here, self‐assembling diblock copolymers are exploited as structure‐directing agents to achieve mesoporous ZnO thin films with highly tailorable structural characteristics ranging from nanomorphologies, over crystalline levels, to defect contents. As verified by theoretical calculations, the presence of oxygen vacancy will facilitate favorable water adsorption and subsequent dissociation on the polar ZnO surfaces. Upon humidity exposure with progressively increased levels, mesoporous ZnO films are revealed to follow an almost positive relationship between adsorption and electrical conductivity but show superior morphological stability. This work not only elucidates the water‐governed ZnO surface chemistry but may also promote a comprehensive understanding of the morphology‐function relationship on ZnO‐based electronics. [ABSTRACT FROM AUTHOR]

While Ta3N5 shows excellent potential as a semiconductor photoanode for solar water splitting, its performance is hindered by poor charge carrier transport and trapping due to native defects that introduce electronic states deep within its bandgap. Here, it is demonstrated that controlled Ti doping of Ta3N5 can dramatically reduce the concentration of deep‐level defects and enhance its photoelectrochemical performance, yielding a sevenfold increase in photocurrent density and a 300 mV cathodic shift in photocurrent onset potential compared to undoped material. Comprehensive characterization reveals that Ti4+ ions substitute Ta5+ lattice sites, thereby introducing compensating acceptor states, reducing the concentrations of deleterious nitrogen vacancies and reducing Ta3+ states, and thereby suppressing trapping and recombination. Owing to the similar ionic radii of Ti4+ and Ta5+, substitutional doping does not introduce lattice strain or significantly affect the underlying electronic structure of the host semiconductor. Furthermore, Ti can be incorporated without increasing the oxygen donor content, thereby enabling the electrical conductivity to be tuned by over seven orders of magnitude. Thus, Ti doping of Ta3N5 provides a powerful basis for precisely engineering its optoelectronic characteristics and to substantially improve its functional characteristics as an advanced photoelectrode for solar fuels applications. [ABSTRACT FROM AUTHOR]