Interfaces in perovskite and organic solar cells play a central role in advancing efficiency and prolong device durability. They improve charge transport/transfer from the absorber layer to the collecting electrodes, while also blocking the opposite charge carriers, minimize voltage losses by suppressing charge recombination. and may act as buffer/protective layers and nanomorphology regulators for the absorber layer. One such interface is formed by the hole transport layer (HTL) and the organic/perovskite absorber. These HTLs typically consist of organic semiconductors, which, although are solution processable at low temperatures and allow perfect energy‐level alignment with the absorber layer and therefore efficient charge collection, are prone to degradation in ambient conditions and under continuous light exposure. In a quest for robust alternatives, inorganic materials such as metal oxides, graphene oxide, bronzes, copper thiocyanate, and transition metal dichalcogenides are actively investigated. However, their hole extraction capability is inferior compared with organic semiconductors as they possess specific energetics leading to significant charge extraction barriers and moderate charge collection. To achieve further advancements in their hole transporting capabilities, strongly interconnecting knowledge of their synthesis, electronic properties, and device performance metrics is required.

Understanding how absorbed hydrogen affects properties of metals is important in hydrogen storage and transportation as well as degradation of metal interconnects in devices and other applications. It has been suggested that hydrogen can promote the formation of vacancies and play a significant role in voiding phenomena in Cu. Because it is still challenging to measure the amount of H incorporated into metals, computational modelling has been playing in important role in achieving that. However, thermodynamic limits of hydrogen storage in pure Cu remain controversial. Our computational study employs statistical thermodynamics to determine equilibrium molar fractions of copper vacancies (V_Cu), H interstitials (H_i) and their complexes in bulk Cu in a wide range of temperature and hydrogen pressure values. The results show that the equilibrium molar fractions of both V_Cu and H_i are low in most conditions of interest, in good agreement with available experimental data. Although H_i - V_Cu complexes have significantly lower formation energies than the isolated defects, the low molar fraction of H is predicted to have little impact on the rise in vacancy molar fraction for external hydrogen pressures below 100 bar. Only at relatively high hydrogen pressures exceeding 10 kbar in the presence of Cu vacancies, H molar fraction was found to reach the same order of magnitude as the molar fraction of vacancies. These results put thermodynamic limits on the hydrogen-induced vacancy clustering and void formation in bulk Cu.

The mechanical properties of CuTi alloys have been characterized extensively through experimental studies. However, a detailed understanding of why the strength of Cu increases after a small fraction of Ti atoms are added to the alloy is still missing. In this work, we address this question using density functional theory (DFT) and molecular dynamics (MD) simulations with the modified embedded atom method (MEAM) interatomic potentials. First, we performed calculations of the uniaxial tension deformations of small bicrystalline Cu cells using DFT static simulations. We then carried out uniaxial tension deformations on much larger bicrystalline and polycrystalline Cu cells by using MEAM MD simulations. In bicrystalline Cu, the inclusion of Ti increases the grain boundary separation energy and the maximum tensile stress. The DFT calculations demonstrate that the increase in the tensile stress can be attributed to an increase in the local charge density arising from Ti. MEAM simulations in larger bicrystalline systems have shown that increasing the Ti concentration decreases the density of the stacking faults. This observation is enhanced in polycrystalline Cu, where the addition of Ti atoms, even at concentrations as low as 1.5 atomic (at.) %, increases the yield strength and elastic modulus of the material compared to pure Cu. Under uniaxial tensile loading, the addition of small amounts of Ti hinders the formation of partial Shockley dislocations in the grain boundaries of Cu, leading to a reduced level of local deformation. These results shed light on the role of Ti in determining the mechanical properties of polycrystalline Cu and enable the engineering of grain boundaries and the inclusion of Ti to improve degradation resistance.

Voids in face-centered cubic (fcc) metals are commonly assumed to form via the aggregation of vacancies; however, the mechanisms of vacancy clustering and diffusion are not fully understood. In this study, we use computational modeling to provide a detailed insight into the structures and formation energies of primary vacancy clusters, mechanisms and barriers for their migration in bulk copper, and how these properties are affected at simple grain boundaries. The calculations were carried out using embedded atom method (EAM) potentials and density functional theory (DFT) and employed the site-occupation disorder code (SOD), the activation relaxation technique nouveau (ARTn) and the knowledge led master code (KLMC). We investigate stable structures and migration paths and barriers for clusters of up to six vacancies. The migration of vacancy clusters occurs via hops of individual constituent vacancies with di-vacancies having a significantly smaller migration barrier than mono-vacancies and other clusters. This barrier is further reduced when di-vacancies interact with grain boundaries. This interaction leads to the formation of self-interstitial atoms and introduces significant changes into the boundary structure. Tetra-, penta-, and hexa-vacancy clusters exhibit increasingly complex migration paths and higher barriers than smaller clusters. Finally, a direct comparison with the DFT results shows that EAM can accurately describe the vacancy-induced relaxation effects in the Cu bulk and in grain boundaries. Significant discrepancies between the two methods were found in structures with a higher number of low-coordinated atoms, such as penta-vacancies and di-vacancy absortion by grain boundary. These results will be useful for modeling the mechanisms of diffusion of complex defect structures and provide further insights into the structural evolution of metal films under thermal and mechanical stress.

Two‐dimensional (2D) transition metal dichalcogenides (TMDs) are being explored in electronic and optoelectronic applications, including electrochemical random‐access memories (ECRAMs). ECRAMs are three‐terminal electrochemical neuromorphic devices in which a gate bias inserts or extracts ions (e.g., H ⁺ ) into or from a channel through a solid electrolyte, thereby modulating its conductivity. In thin‐film oxide channels, post‐pulse ion diffusion into the channel depth gives rise to a slow transient in obtaining the stable conductance state. Monolayer 2D TMD channels eliminate channel depth and could remove this contribution to transient, accelerating device programming. However, whether H insertion can modulate conductivity in 2D TMD channels remains to be determined. Here, we assess hydrogen incorporation at monolayer MoS ₂ /SiO ₂ interfaces using atomistic simulations with varying SiO ₂ surface terminations. In the absence of sulfur vacancies, H favors incorporation on the SiO ₂ surface when dangling bonds are present, leaving MoS ₂ electronically decoupled from H. Once the oxide surface is saturated, H adsorbs onto or incorporates into MoS ₂ , acting as an n‐type dopant. With sulfur vacancies, H stably incorporates into the vacancy and produces a similar n‐type effect. We experimentally verified these predictions in protonic ECRAM devices with monolayer MoS ₂ channels: hydrogen insertion increased conductance, while hydrogen extraction decreased it, consistent with electron doping. Our findings confirm that H can modulate the conductivity of 2D monolayer MoS ₂ channel at the interface with oxide electrolytes in ECRAMs and provide the underlying mechanisms.