Grain boundaries in lithium lanthanum zirconate solid-state electrolytes feature elevated electronic conduction and act as preferential sites for the nucleation of electrically isolated lithium metal during galvanostatic cycling in battery cells. However, the origin of local electronic conductivity variations remains unresolved. Here we show that lithium lanthanum zirconate grain boundaries carry ionic built-in charge, with lithium vacancies accumulating at the interface generating localized electric potentials (-0.15 V at 20 °C). This potential alters carrier distributions near the grain boundary, impeding ionic transport and increasing electronic conduction by a factor of 30 compared with bulk. This imbalance initiates internal lithium metal nucleation during cell operation and accelerates short-circuit failure. To mitigate charge build-up, we propose tailoring the processing oxygen activity and dopant stoichiometry, precisely tuning atomic-scale chemistry and interfacial potential. These modifications homogenize ionic transport and reduce electronic leakage, enabling the intrinsic critical current density to 1 mA cm-2. Our findings uncover how local defect landscapes shape charge transport and provide a pathway for chemically guided optimization of inorganic solid-state electrolytes at the nanoscale.

Abstract Understanding how material and defect characteristics govern photoelectrochemical performance is essential for developing efficient and stable photoelectrodes. Although bulk properties are often emphasized, surfaces and interfaces can equally determine activity and stability under operation. Here, we use depth-sensitive characterization to disentangle surface and bulk properties of Ta 3 N 5 thin films. By preparing photoelectrodes from TaO x , TaN x , and Ta precursors, we systematically vary shallow and deep-level defect concentrations. Structural, compositional, and optoelectronic analyses show that the surfaces consistently exhibit oxygen enrichment, increased structural disorder, and higher deep-level defect densities than the bulk. However, the specific surface structure and its spatial extent depend strongly on precursor chemistry. Ta 3 N 5 derived from TaO x forms an extended, amorphous, oxide-rich surface with fewer deep-level defects, whereas TaN x and Ta-derived Ta 3 N 5 films exhibit thinner, more crystalline surfaces with increased mid-gap defect densities. A brief hydrofluoric acid treatment removes the disordered surface layer, improving crystallinity and hydrophilicity and enhancing photoelectrochemical performance and stability for ferrocyanide oxidation. These results highlight interfacial and defect engineering as routes toward durable, high-efficiency Ta 3 N 5 photoelectrodes.

Abstract Metal halide perovskite solar cells combine high power density with low-cost manufacturing, but durability under repeated extreme temperature cycling remains insufficiently understood. We investigate thermal fatigue under cycling between −80 °C and +80 °C as an accelerated stress protocol. Mismatched thermal expansion between the perovskite absorber and glass substrate induces biaxial tensile strain, leading to degradation at the substrate–perovskite interface and within grain boundaries. To mitigate these failure modes, we introduce a co-additive molecular strategy based on lipoic acid, dihydrolipoic acid, and a sulfonium-based derivative to enhance interfacial adhesion, while in situ polymerization during annealing reinforces grain-boundary cohesion. This dual reinforcement improves robustness and performance, achieving stabilized efficiencies of 26% under standard solar illumination. Devices retain 84% of initial efficiency after 16 extreme temperature cycles. Our experiments reveal that thermal exposure duration is more critical than cycle number, with most degradation occurring during initial cycles.

Optoelectronic performance, defect density, and thin-film morphology of solution-processable lead halide perovskites are highly dependent on nucleation and growth conditions during processing. Additionally, Cs+ incorporation into the lattice can have benign effects on the thin films, which is challenging for scalable, deposition-friendly solvents such as 2-methoxyethanol or acetonitrile due to their highly limited solubility of Cs-containing salts. To address both issues, we present an interface-engineering approach that utilizes CsPbI3 nanocubes as seed crystals for slot-die coating of FAPbI3. The seeds improve growth-control at the bottom interface and enhance Cs+ incorporation into the active layer lattice. Incidence angle varied grazing-incidence wide-angle X-ray scattering enables depth-resolved structural probing of thin films, revealing increased Cs+ incorporation with increasing film depth. Additionally, morphological parameters, such as thin-film "face-on" orientation and crystallographic texture, are significantly improved in the seeded film. Accordingly, the seeded films exhibit reduced defect density and enhanced charge-carrier separation due to increased structural ordering and Cs+ alloy-induced bandgap tuning across the active layer thickness. Resulting p-i-n photovoltaic devices exhibit superior mean values as well as a narrower spread across short-circuit current density, fill factor, and power conversion efficiency, highlighting the beneficial effects of nanocrystal seeding on active-layer quality and reproducibility.

Ta_3N_5 is among the most intensively studied photoanode materials for solar-driven water oxidation, yet its performance often remains limited by short carrier lifetimes and defect mediated recombination. Although transient absorption spectroscopy is widely used to probe carrier dynamics in photoelectrodes, spectral assignments are frequently ambiguous due to overlapping contributions. Here, microsecond-to-second transient absorption of Ta_3N_5 thin films is combined with complementary optical spectroscopies to disentangle contributions from lattice heating, electrostatics, and defect states. Photoreflectance reveals three critical points in the Ta_3N_5 band structure, including two anisotropic near-edge transitions at 2.14 eV and 2.27 eV and a higher-lying transition near 2.80 eV, all closely aligned with dominant transient absorption features. A previously unreported photo-induced absorption at 2.80 eV is attributed to pump-induced lattice heating, while potential-dependent measurements reveal that near-edge bleach features arise from pump-induced band flattening and subsequent surface photovoltage relaxation. Fitting transient absorption spectra with independently measured thermal and electrostatic components enables quantification of both thermal and photovoltage dynamics, while the sub-bandgap response provides insight into the redistribution of defect charge states. Thus, this approach to quantifying thermal, electrostatic, and defect-mediated contributions to microsecond-to-second transient absorption provides broadly applicable insights into photoexcitation and relaxation mechanisms in functional semiconductor photoelectrodes.

The oxygen evolution reaction remains a kinetic and stability bottleneck in different (photo)electrochemical energy conversion systems, motivating the development of novel, earth-abundant catalyst coatings that simultaneously enhance surface activity and protect interface properties. Here, we synthesize cobalt nitride thin films via plasma-enhanced atomic layer deposition and evaluate their application as multifunctional catalysts and protection layers under alkaline conditions. By varying the deposition temperature, we systematically tune the film composition and elucidate composition-function relationships that govern catalytic performance and durability. Films deposited at <= 150 degrees C exhibit incomplete precursor conversion and substantial carbon impurity incorporation, resulting in poor catalytic activity and rapid mechanical failure. In contrast, depositions at 200 degrees C and 250 degrees C form cobalt nitride films with lower N/Co ratios, reduced oxygen and carbon impurity concentrations, yielding catalytically active coatings with operational stability. Post-operando analysis reveals surface oxidation, suggesting that oxygen evolution activity may be governed by an oxide-derived layer rather than the nitride phase. Importantly, compared to cobalt oxide, cobalt nitrides can suppress substrate surface oxidation by using ammonia plasma as an oxygen-free co-reactant, thereby enabling favorable interface properties for hole extraction. Taken together, cobalt nitride layers are highly promising for engineering stable, high-performance catalytic interfaces in energy conversion systems.

Direct solar water splitting is a promising approach for sustainably producing hydrogen, but significant materials challenges must be overcome to achieve high efficiency and long‐term stability. This work demonstrates a tailored interface treatment combined with multifunctional surface coatings that significantly enhance the efficiency and lifetime of GaAs/GaInP tandem cells capable of unassisted solar water splitting. In particular, it is shown that exposure of the top AlInP window layer to a remote H 2 plasma effectively reduces the interfacial oxide, enhancing charge extraction and maximizing the available photovoltage. Subsequent atomic layer deposition (ALD) of a bilayer coating comprising a TiO 2 corrosion protection layer and Pt nanoparticles enhances the durability of the device, enables efficient electron extraction, and provides high catalytic activity. By tuning the Pt ALD process, a nanoparticulate morphology is achieved, ensuring high catalytic activity at low loading, thus minimizing parasitic light absorption and improving adhesion. The optimized dual‐junction photoelectrode achieves an initial maximum solar‐to‐hydrogen (STH) conversion efficiency of 17.1%, stabilizing at 16.2% for 170 min of continuous operation. Importantly, the tailored interfaces of the device result in a considerable photovoltage surplus, providing a route to systems offering higher STH efficiencies or for integration of Group III‐V semiconductor‐on‐Si tandems.

Zinc nitride (Zn3N2) comprises earth-abundant elements, possesses a small direct bandgap, and is characterized by high electron mobility. While these characteristics make the material a promising compound semiconductor for various optoelectronic applications, including photovoltaics and thin-film transistors, it commonly exhibits unintentional degenerate n-type conductivity. This degenerate character has significantly impeded the development of Zn3N2 for technological applications and is commonly assumed to arise from incorporation of oxygen impurities. However, consistent understanding and control of the role of native and impurity defects on the optoelectronic properties of this otherwise promising semiconductor have not yet emerged. Here, we systematically synthesize epitaxial Zn3N2 thin films with controlled oxygen impurity concentrations of up to 20 at % by plasma-assisted molecular beam epitaxy (PA-MBE). Contrary to expectations, we find that oxygen does not lead to degenerate conductivity but instead serves as a compensating defect, the control of which can be used to achieve nondegenerate semiconducting thin films with free electron concentrations in the range of 1017 cm-3, while retaining high mobilities in excess of 200 cm2 V-1 s-1. This understanding of the beneficial role of oxygen thus provides a route to controllably synthesize nondegenerate O-doped Zn3N2 for optoelectronic applications.

Semiconducting ternary nitrides are a promising class of materials that have received increasing attention in recent years, but often show high free electron concentrations due to the low defect formation energies of nitrogen vacancies and substitutional oxygen, leading to degenerate n-type doping. To achieve non-degenerate behavior, we now investigate a family of amorphous calcium-zinc nitride (Ca-Zn-N) thin films. By adjusting the metal cation ratios, we demonstrate band gap tunability between 1.4 and 2.0 eV and control over the charge carrier concentration across six orders of magnitude, all while maintaining high mobilities between 5 and 70 cm2 V-1 s-1. The combination of favorable electronic properties, low synthesis temperatures, and earth-abundant elements makes amorphous Ca-Zn-N highly promising for future sustainable electronics. Moreover, the successful synthesis of such materials, as well as their broad optical and electrical tunability, paves the way for a new class of tailored functional materials: amorphous nitride semiconductors - ANSs.

Electro- and photodriven catalysis are emerging as viable alternatives to traditional catalytic methods for producing key global consumer products across various applications. The emergence of this class of catalysis is attributable to increasing need for sustainable and ecofriendly pathways to value-added chemical synthesis. The roadmap for the highly diverse and multifaceted field of catalysis continues to evolve, highlighting the growing need of understanding their physical and chemical reaction mechanism. Among the many available characterization techniques, in situ and operando investigations stand out for their ability to provide detailed insights into fundamental physicochemical processes under realistic working conditions. In this article, a select group of representative energy material is discussed, where the application of different in situ/operando techniques successfully generates improved understanding. The primary goal is to emphasize the significance of these techniques, particularly those, which have been commonly employed in studying materials relevant to energy and environmental applications.

Combining a precise sputter etching method with subsequent AlOx growth within an atomic layer deposition chamber enables the fabrication of atomically flat lateral patterns of SiO2 and AlOx. The transfer of MoSe2 monolayers onto these dielectrically modulated substrates results in the formation of lateral heterojunctions due to the interaction with alternating regions of SiO2 and AlOx, with the flat substrate topography leading to minimal strain across the junction. Kelvin probe force microscopy measurements show significant variations in the contact potential difference (CPD) across the interface, with AlOx regions inducing a 230 mV increase in CPD. Photoluminescence spectroscopy reveals shifts in spectral weight of neutral and charged exciton species across the different dielectric regions. On the AlOx side, the Fermi energy moves closer to the conduction band, leading to a higher trion-to-exciton ratio, indicating a bandgap shift consistent with CPD changes. In addition, transient reflection spectroscopy highlights the influence of the dielectric environment on carrier dynamics, with the SiO2 side exhibiting rapid carrier decay typical of neutral exciton recombination. In contrast, the AlOx side shows slower, mixed decay behavior consistent with conversion of trions back into excitons. These results demonstrate how dielectric substrate engineering can tune 2D materials, allowing scalable fabrication of advanced junctions for novel (opto)electronics applications.

We investigate the interplay between vertical tunneling and lateral transport phenomena in electrically contacted van der Waals heterostructures made from monolayer MoS2, hBN, and graphene. We compare data taken by low-temperature scanning tunneling spectroscopy to results from room-temperature conductive atomic force spectroscopy on monolayer MoS2 with sulfur vacancies and with varying hBN layers. We show that for thick hBN barrier layers, where tunneling currents into the conductive substrate are suppressed, a side-contact still enables addressing the defect states in the scanning tunneling microscopy via the lateral current flow. Few-layer hBN realizes an intermediate regime in which the competition between vertical tunneling and lateral transport needs to be considered. The latter is relevant for device structures with both a thin tunneling barrier and a side-contact to the semiconducting layers.

The photoelectrochemical performance of Ta3N5 photoanodes is strongly impacted by the presence of shallow and deep defects within the bandgap. However, the role of such states in defining stability under operational conditions is not well understood. Here, a highly controllable synthesis approach is used to create homogenous Ta3N5 thin films with tailored defect concentrations to establish the relationship between atomic-scale point defects and macroscale stability. Reduced oxygen contents increase long-range structural order but lead to high concentrations of deep-level states, while higher oxygen contents result in reduced structural order but beneficially passivate deep-level defects. Despite the different defect properties, the synthesized photoelectrodes degrade similarly under water oxidation conditions due to the formation of a surface oxide layer that blocks interfacial hole injection and accelerates charge recombination. In contrast, under ferrocyanide oxidation conditions, it is found that Ta3N5 films with high oxygen concentrations exhibit long-term stability, whereas those possessing lower oxygen contents and higher deep-level defect concentrations rapidly degrade. These results indicate that deep-level defects result in rapid trapping of photocarriers and surface oxidation but that shallow oxygen donors can be introduced into Ta3N5 to enable kinetic stabilization of the interface.

AgBiS2 quantum dots (ABS QDs) have emerged as highly promising candidates for photovoltaic applications due to their strong sunlight absorption, nontoxicity, and elemental availability. Nevertheless, the efficiencies of ABS solar cells currently fall far short of their thermodynamic limits due in large part to sluggish charge transport characteristics in nanocrystal-derived films. In this study, we overcome this limitation by tuning the surfaces of ABS semiconductor QDs via a solvent-induced ligand exchange (SILE) strategy and provide key insights into the role of surface composition on both n- and p-type charge transfer doping, as well as long-range charge transport. Using this approach, the electronic properties of ABS films were systematically modulated, thereby enabling the design of planar p-n heterojunctions featuring favorable band alignment for solar cell applications. Carrier transport and separation are significantly enhanced by the built-in electric fields generated within the ultrathin (30 nm) ABS heterojunction absorber layers, resulting in a notable solar-cell power conversion efficiency of 7.43%. Overall, this study presents a systematic and straightforward strategy to tune not only the surfaces of ABS, but also the electronic properties of solid-state films, thereby enabling junction engineering for the development of advanced semiconductor structures tailored for photovoltaic applications.

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.

Ternary nitrides are rapidly emerging as promising compounds for optoelectronic and energy conversion applications, yet comparatively little of this vast composition space has been explored. Furthermore, the crystal structures of these compounds can exhibit a significant amount of disorder, the consequences of which are not yet well understood. Here, the deposition of bixbyite-type ZrTaN3 thin films is demonstrated by reactive magnetron co-sputtering and observed semiconducting character, with a strong optical absorption onset at 1.8 eV and significant photoactivity, with prospective application as functional photoanodes. It is found that Wyckoff-site occupancy of cations is a critical factor in determining these beneficial optoelectronic properties. First-principles calculations show that cation disorder leads to minor deviations in the total energy but modulates the bandgap by 0.5 eV, changing orbital hybridization of valence and conduction band states. In addition to demonstrating that ZrTaN3 is a promising visible light-absorbing semiconductor and active photoanode material, the findings provide important insights regarding the role of cation ordering on the electronic structure of ternary semiconductors. In particular, it is shown that not only cation order, but also the cationic Wyckoff site occupancy has a substantial impact on key optoelectronic properties, which can guide future design and synthesis of advanced semiconductors.

Transition metal oxynitrides are a promising class of functional materials for photoelectrochemical (PEC) applications. Although these compounds are most commonly synthesized via ammonolysis of oxide precursors, such synthetic routes often lead to poorly controlled oxygen-to-nitrogen anion ratios, and the harsh nitridation conditions are incompatible with many substrates, including transparent conductive oxides. Here, we report direct reactive sputter deposition of a family of zirconium oxynitride thin films and the comprehensive characterization of their tunable structural, optical, and functional PEC properties. Systematic increases of the oxygen content in the reactive sputter gas mixture enable access to different crystalline structures within the zirconium oxynitride family. Increasing oxygen contents lead to a transition from metallic to semiconducting to insulating phases. In particular, crystalline Zr2ON2-like films have band gaps in the UV-visible range and are n-type semiconductors. These properties, together with a valence band maximum position located favorably relative to the water oxidation potential, make them viable photoanode candidates. Using chopped linear sweep voltammetry, we indeed confirm that our Zr2ON2 films are PEC-active for the oxygen evolution reaction in alkaline electrolytes. We further show that high-vacuum annealing boosts their PEC performance characteristics. Although the observed photocurrents are low compared to state-of-the-art photoanodes, these dense and planar thin films can offer a valuable platform for studying oxynitride photoelectrodes, as well as for future nanostructuring, band gap engineering, and defect engineering efforts.