Nanoscale imaging of charge carrier transport in water splitting photoanodes

Abstract

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.

Emerging Conductive Atomic Force Microscopy for Metal Halide Perovskite Materials and Solar Cells

“…C‐AFM as a high‐sensitive characterization technique has been used to probe charge transport and electronic properties by measuring current under short‐circuit conditions . Generally, a large current under the same test condition indicates high conductivity of sample, which is beneficial to charge transport . On this basis, the conductivity discrepancy among different films can be studied and the transport behavior in grain interiors and at grain boundaries can be distinguished by C‐AFM with the nanoscale resolution.…”

Ultra‐Narrow Depletion Layers in a Hematite Mesocrystal‐Based Photoanode for Boosting Multihole Water Oxidation

“…Although electrochemical measurements can macroscopically analyze the properties of photoanodes, the nanoscopic variations within the electrode or single particle are still not able to be determined by such ensemble experiments. We thus employed photoconductive atomic force microscopy (pc‐AFM) to elucidate structure‐correlated electrical transport properties inherent in individual MC particles with nanoscale resolution (Figure c–e; Supporting Information, Figure S11). Bias potentials ranging from −1.0 to 1.0 V were applied to the sample using a Ti/Ir‐coated conductive probe with a 25 nm tip radius, and the current was simultaneously collected under dark conditions or light irradiation in an N 2 atmosphere.…”

“…20 nm) showed a current onset (>0.25 V) in the low potential region (Figure e) due to Schottky contact. Schottky emission is an interface‐limited conduction that occurs at low voltages, whereby electrons transit above the potential barrier on the surface of a semiconductor . Both the Poole–Frenkel and Schottky emissions originate from lowering of the Coulombic potential barrier for free‐charge generation out of defect centers or trap sites under a bias potential .…”

Disentangling the Role of Surface Chemical Interactions on Interfacial Charge Transport at BiVO4 Photoanodes

“…The BiVO 4 thin films were illuminated from the FTO-side as in Ref. [16] . A CW-laser diode laser (405 nm) was used as light source.…”