The oxygen‐K pre‐edge has been broadly used to discuss the oxygen redox states in batteries. Here, through combined experimental and in theoretical studies of a number of oxide electrodes, we conclude that the O‐K pre‐edge evolution predominantly represents the transition metal state variation, which is summarized to benchmark future research.

As CuBi 2 O 4 is an emerging p-type semiconductor for applications as a photocathode in photoelectrochemical (PEC) solar fuel production, there is much to be understood about the uniqueness and commonalities the material exhibits in comparison to other, more well-known metal oxide semiconductor systems. We examine p-CuBi 2 O 4 thin films grown by reactive co-sputtering with a comprehensive spectroscopic and first principles characterization methodology to describe its fundamental electronic structure and optical properties while addressing intrinsic limitations in the observed PEC performance. The optical properties are evaluated from 180 to 2500 nm with a multi-modal approach using spectroscopic ellipsometry, UV−vis, and photothermal deflection spectroscopy to obtain the complex dielectric function and 5 orders of magnitude of the absorption coefficient. The films are evaluated under PEC conditions appropriate for CO 2 reduction conditions (0.1 M HCO 3 2− ) with the inclusion of electron scavenger (S 2 O 8 2− ) to minimize catalytic limitations. While the theoretical maximum photocurrent density was 4.68 mA cm −2 , the realized photocurrent was 1.18 mA cm −2 with front-side illumination and an onset potential of about 1.1 V RHE . The thickness dependence of the photocurrent under back-side illumination exposed a limited electron diffusion length of 45 nm attributed to electron small polaron transport. Connections are established between electronic structure, optical properties, and PEC performance through a combination of X-ray spectroscopies (X-ray absorption spectroscopy, X-ray emission spectroscopy, resonant inelastic X-ray scattering, and X-ray photoelectron spectroscopy) and ab initio modeling. These results not only provide the basis for understanding the observed polaron limitations but also form the basis of a broader connection to other material systems which are governed by polaronic limitations. This study provides a conceptual framework to interconnect observations made through the multiple types of advanced characterization methodologies presented. Ultimately, this work aims to assist the development of CuBi 2 O 4 beyond its intrinsic limitations for its application in solar fuel production.

The way in which conjugated polymers pack in the solid state strongly affects the performance of polymer-based optoelectronic devices. However, even for the most crystalline conjugated polymers the precise packing...

Constrained density functional theory (CDFT) is used to evaluate the energy level alignment of a benzene molecule as it approaches a graphene sheet. Within CDFT the problem is conveniently mapped onto evaluating total energy differences between different charge-separated states, and it does not consist in determining a quasiparticle spectrum. We demonstrate that the simple local density approximation provides a good description of the level alignment along the entire binding curve, with excellent agreement to experiments at an infinite separation and to GW calculations close to the bonding distance. The method also allows us to explore the effects due to the presence of graphene structural defects and of multiple molecules. In general, all our results can be reproduced by a classical image charge model taking into account the finite dielectric constant of graphene.