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Contemporary perovskite solar cells (PSCs) have drawn substantial interest due to their high photovoltaic efficiency. However, the instability of perovskite in a humid environment restricts the service time extension and limits the large‐scale application of PSCs. Herein, a series of passivation molecules (PMs), 2‐MEP, 2‐MDEP, 2‐MTEP, and 2‐MQEP, featuring different lengths of alkyl chains have been designed based on 2‐mercaptopyridine (2‐MP) which greatly improve the stability of PSCs in the humid environment. First‐principles calculations demonstrate that the designed molecules offer stronger adsorption on the perovskite surface compared with 2‐MP. The charge density difference and Bader charge analysis show that the newly designed Lewis bases improve the charge transfer ability, leading to effective separation of carriers at PM@MAPbI3 interfaces. Furthermore, molecular dynamics simulations verify that the steady Pb‐N/S interactions in the MAPbI3/PM/H2O system effectively prevent H2O from approaching the perovskite surface. This work not only provides a set of promising surface passivators (especially 2‐MDEP), but also paves a way for the design of PMs that endow PSCs stability and make PSCs highly competitive in the photovoltaic market. [ABSTRACT FROM AUTHOR]

Abstract The properties of three D1-π-D2-A dyes with dithiafulvenyl as donor (D1), phenothiazine as ancillary donor (D2), cyanoacrylic acid as acceptor along with different π groups, diphenyl for 1 , dithienyl for 2 , and thiopheneyl-benzothiadiazole for 3 , are studied. Besides the isolated dyes, the monomeric and dimeric adsorptions are also studied by combination of first principle and molecular dynamic simulations. There is no distinct difference among three dyes on the basis of only isolated dyes. When the dye-TiO 2 adsorption is considered, 3 is excluded because of its inferior items. However, it is still a difficult task to differentiate 1 and 2 even if the aggregation effect is included. The fluctuation of 1 is larger than that of 2 during the dynamic simulation resulting in the larger electronic coupling. The aggregation, especially for the aggregation during the dynamic simulation, is necessary to evaluate the performance of organic dye. Additionally, a new D-π-A dye 4 with the identical donor, π-bridge and acceptor is designed to compare with 2. 2 is totally superior to 4 indicating that suitable groups and appropriate configuration are both important to enhance the performance of organic dye. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Aggregation is inevitable for the organic dyes, and it is difficult to evaluate its effects due to its complexity. Herein, we combine first principles and molecular dynamics (MD) simulations to explore the influence of aggregation on the optical and electronic properties for THI-BTZ-2T-C . If only the static properties are considered, the configuration of dye is not varied greatly when the adsorbed dyes are increased from monomer to hexamer. However, the absorption spectrum varies regularly with the increased aggregation order. In addition, the contribution of different orbitals of various atoms to density of states (DOS) gradually increases with the aggregation order increasing. When dynamics simulation is performed, the torsion between different components of dye is enlarged. Meanwhile, the perpendicular model is altered during the dynamics simulations, the dye would like to bend towards the TiO 2 surface. Moreover, the electronic coupling is greatly improved during the molecular dynamics simulations especially for the H-aggregation. The dye aggregation mainly affects the electrons injection process resulting in the reduction of the photoelectric conversion efficiency for dye sensitized solar cells (DSSCs). Reduction of perfect face to face stacking would be an efficient pathway to weaken the aggregation. [ABSTRACT FROM AUTHOR]

Interfacial properties between passivation molecules and perovskite surface determine passivation effects on the performance and stability of perovskite solar cells. [Display omitted] • Passivation effect is related to binding strength and probability. • Strong polarity of 2-MP enhances charge separation and adsorption capacity. • 2-MP passivation improves carrier transfer capability. • 2-MP passivation leads to large bandgap. • AIMD simulations reveal water blocking effects of 2-MP, Py, and PTT. Chemical passivation implemented by Lewis base has been demonstrated as an effective method to overcome the water vulnerability of perovskite solar cells (PSCs) along with better performance. Comprehensive understanding of the surface passivation effects is crucial to future improve the PSCs efficiency and stability. Herein, we utilized first-principles to simulate the structure and electronic properties of the passivated perovskite, and carried out ab initio molecular dynamics (AIMD) to understand the effectiveness of the experimental passivation molecules, 2-MP , Py , and PTT , on the classical perovskite (Zhu et al., 2019). Calculations show that introducing both -SH and the N atom of 2-MP enhances the electric dipole moment, the binding strength, the adsorption probability and the carrier transfer rate compared to these of Py and PTT. Moreover, the efficient separation of electrons and holes at the interface and the large bandgap can be achieved by the 2-MP treatment, which is beneficial to improve the photovoltaic performance. AIMD simulations indicate that the interactions of N⋯Pb, S⋯Pb, and H⋯I between 2-MP and the MAPbI 3 surface lead to a stronger passivation effect than that of Py and PTT , which is in agreement with the experimental observations. Our results are expected to provide new ideas for developing more distinguished passivation molecules to endow the PSCs stability against water. [ABSTRACT FROM AUTHOR]

Abstract The knowledge of viscosity about ionic liquids is important for their large scale-up application. Although some theoretical models and experimental methods are developed to evaluate the viscosity, there are some common disadvantages for them including complexity, time consuming, and unreliable. It is necessary to develop a simple method to evaluate the viscosity. Even if the accurate value of viscosity could not be obtained, the relative sequence for a series of ionic liquids with similar structures is still beneficial for their applications. The relationship between hydrogen bond and viscosity for TBA pyruvate, TBA L‐lactate, and TBA L‐malate are studied by combination of molecular dynamics simulation and quantum chemistry methods. The strength of hydrogen bond in TBA L‐malate is the larger resulting in the larger viscosity. In contrast, the number of hydrogen bond has a minor influence on the viscosity. It is expected that this study would provide some useful information to build the relationship between hydrogen bond and viscosity for task functionalized ionic liquids. Graphical abstract Unlabelled Image Highlights • Relationship between hydrogen bond and viscosity • The inclusion of hydroxyl group is helpful to improve the strength of hydrogen bonds. • Strength of hydrogen bonds is determined items for viscosity rather than the number. [ABSTRACT FROM AUTHOR]

The excellent catalytic activity of [N 2,2,2,2OH ][SA] is traced to the critical role played by nucleophilic-electrophilic dual activation from [SA]- anions in the cycloaddition reaction of CO 2. [Display omitted] • The catalytic mechanism of carboxylate anion-based ionic liquids is firstly elucidated in this work. • The catalytic role of carboxylate anions is complex and flexible. • The underlying electrophilic activation ability of the carboxylic acid anion plays a critical role in enhancing the catalytic activity. • The electrophilic activation plays a more important role than nucleophilic activation in the ring-opening step. Elucidating the mechanism of carbon dioxide (CO 2) cycloaddition reaction catalyzed by ionic liquid (ILs) facilitates the rational design of efficient IL catalysts at the molecular level. To date, a great deal of research has been devoted to the halogen-containing ILs, however, the catalytic mechanism of halogen-free ILs remains unclear. In this contribution, an exhaustive theoretical study of the coupling reaction of CO 2 with epichlorohydrin (ECH) catalyzed by three halogen-free ILs has been carried out for the first time by combining density functional theory (DFT) calculations with molecular dynamics (MD) simulations. Meanwhile, the effect of carboxylate anion structure on catalytic activity is deeply investigated. The final results provide a comprehensive catalytic mechanism of carboxylate anion-based ILs. The most favorable mechanism involves three steps, i.e., ring-opening of ECH, CO 2 insertion, and ring-closure to form the product. Among them, the ring-opening of ECH is the rate-determining step (RDS). Additionally, the analytical results of the independent gradient model based on Hirshfeld partition (IGMH) and atoms in molecules (AIM) suggest that the electrophilic activation from carboxylate anions plays a critical role in promoting the ECH ring-opening process. The electrophilic activation of anions is investigated for the first time in this work. The results indicate that incorporating electrophilic groups into anions is a promising pathway to develop new robust and efficient halogen-free ILs. [ABSTRACT FROM AUTHOR]