binding energies of electron-hole pairs, [1] and long carrier diffusion lengths. [2] Most state-of-the-art perovskite solar cells typically consist of either mesoporous [3] or planar heterojunction device architectures. [4] The mesoporous perovskite solar cells consist of a device structure that is based on a mesoporous (or mesosuperstructured) metal oxide scaffold (for example, TiO 2 or Al 2 O 3 ) and the organometal halide perovskites are then infiltrated into the mesoporous metal oxides as light harvesting materials. [3,5] In parallel to the mesoporous architecture, the planar heterojunction perovskite solar cells have a simple device structure with the perovskite films sandwiched between electron and hole transporting layers. [5b] For high-performance perovskite solar cells consisting of either mesoporous or planar heterojunction device architectures, electron transporting layers (ETLs) and hole transporting layers (HTLs) are usually used to extract both photogenerated electrons and holes in the perovskite light absorber layers toward two opposite electrodes. In addition, the appropriate design of the interfacial ETLs and HTLs with well-matched energy levels between electrodes and perovskite light absorbers is known to be responsible to maximize the built-in potential and the open circuit voltage of devices. [6] A novel atomic stacking transporting layer (ASTL) based on 2D atomic sheets of titania (Ti 1−δ O 2 ) is demonstrated in organic-inorganic lead halide perovskite solar cells. The atomically thin ASTL of 2D titania, which is fabricated using a solution-processed self-assembly atomic layer-by-layer deposition technique, exhibits the unique features of high UV transparency and negligible (or very low) oxygen vacancies, making it a promising electron transporting material in the development of stable and high-performance perovskite solar cells. In particular, the solution-processable atomically thin ASTL of 2D titania atomic sheets shows superior inhibition of UV degradation of perovskite solar cell devices, compared to the conventional high-temperature sintered TiO 2 counterpart, which usually causes the notorious instability of devices under UV irradiation. The discovery opens up a new dimension to utilize the 2D layered materials with a great variety of homostructrual or heterostructural atomic stacking architectures to be integrated with the fabrication of large-area photovoltaic or optoelectronic devices based on the solution processes.

Ionic liquids (ILs) show a promising future as electrolytes in electrochemical devices. In particular, IL-based electrolytes bring operations at extreme temperatures to realization that conventional electrolytes fail to accomplish. Although IL electrolytes demonstrate considerable progress in high-temperature applications, their breakthroughs in devices operating at low temperatures are still very limited due to undesirable phase transitions and unsatisfying transport properties. In this study, we present an approach where, by tuning molecular interactions in the system, the designed electrolyte of an IL-based mixture can reach a lower operating temperature with improved transport properties. We have discovered that the incorporation of the IL, ethylammonium nitrate ([EA]­[N]), can contribute to reforming the molecular interactions within the system, which effectively resolve the crystallization accompanied with the excess of water and retain a low glass transition temperature. The reported liquid electrolyte systems based on a mixture of 1-butyl-3-methylimidazolium iodide ([BMIM]­[I]), [EA]­[N], water, and lithium iodide exhibit a glass transition temperature below −105 °C. Furthermore, the optimized electrolyte system shows significant viscosity reduction and ionic conductivity enhancement from 25 to −75 °C. The influence is also noticeable on the increased ionicity, which made the developed electrolyte comparable with other good ILs under the Walden rule. The electrochemical stability of the electrolyte system is revealed by a steady and reproducible profile of iodide/triiodide redox reactions at room temperature over a proper potential window via cyclic voltammetry. The results from this work not only provide a potential solution to applications of the iodide/triiodide redox couple-based electrochemical devices at low temperatures but also show a practical approach to obtain tailored properties of a mixture system via modifying molecular interactions.

Optimized intermolecular interactions by incorporating the organic solvents GBL and PC with an IL lead to enhancements in thermal and transport properties.

Imidazolium-based ionic liquids are well known for their versatility as solvents for various applications such as dyesensitized solar cells, fuel cells, and lithium-ion batteries; however, their complex interactions continue to be investigated to further improve upon their design. Ionic liquids (ILs) are commonly mixed with co-solvents such as water, organic solvents, or other ionic liquids to tailor their physiochemical properties. To better predict these properties and fundamentally understand the molecular interactions within the electrolyte mixtures, molecular dynamics (MD) simulations are often employed. In this study, MD simulations are performed on ternary solutions containing ionic liquids of 1-butyl-3-methylimidazolium iodide ([BMIM][I]) and ethylammonium nitrate ([EA][NO 3 ]) with increasing concentration of water. As previously reported, these ternary solutions displayed a wide temperature window of thermal stability and electrochemical conductivity. Utilizing MD simulations, the complex intermolecular interactions are identified, and the role of water as a co-solvent is disclosed to correlate with changes in their bulk properties. The MD results, including simulation box snapshots, radial distribution functions, and self-diffusion coefficients, reveal the formation of heterogeneous regimes with increasing water concentration, hydrogen bonding between iodide−water, iodide−[EA] + , and a change in IL ordering when in mixtures containing water. The simulations also display the formation of water aggregates and networks at high water concentrations, which can contribute to the thermal behavior of the respective mixtures. As the design of IL-based electrolytes grows in demand with increasing complexity, this work demonstrates the capability of MD simulations containing multiple constituents and their necessity in material development through identification of microscopic structure−property relationships.

Debonding and delamination in fiber reinforced polymer composites has been a prevailing challenge in modern composite applications, as this form of precursor damage can be crucial to understanding failure in these types of composites. Mechanochemistry may offer a unique solution to monitor these failure modes through the use of mechanophores: molecular units which undergo a specific chemical reaction through mechanical deformation of highly strained bonds present in the molecule. In this work, the fluorescent cinnamoyl mechanophore is grafted to the surface of a glass fiber and incorporated into a glass fiber reinforced polymer (GFRP) composite to monitor the mechanophore activation during loading. Additionally, a thermal and mechanical study is performed to understand the effect of mechanophore surface functionalization on property changes of the resulting composite. This work is indeed successful at producing a composite capable of detecting interphase stresses and damage through monitoring of the fluorescent cinnamoyl mechanophore, allowing for an understanding of how this damage initiates in the material.