Boron-containing electron transport materials based on naphthalene diimide for organic solar cells: a theoretical study.

Electron transport materials (ETMs) are crucial for extracting and transporting electrons from the active layer to the cathode in organic solar cells (OSCs). In this work, we designed a series of ETM candidates (E1-E6) based on the experimentally synthesized (,-dimethylamino)propyl naphthalene diimide (NDIN) molecule by changing the nitrogen (N) atoms with boron (B) atoms at different positions. The electronic properties, electron transfer mobility, and interfacial properties were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT).

Passivation of Perovskite Solar Cells with Natural Flavors: Roles of Hydrogen Bonding in Ion Migration and Moisture Resistance.

The passivation strategy is considered to be an essential approach for enhancing the efficiency and stability of perovskite solar cells (PSCs). Herein, based on density functional theory calculations and ab initio molecular dynamics simulations, we investigated the ion migration and moisture stability for MAPbI passivated with a Lewis base represented by natural molecules: cinnamaldehyde (CA) and anethole (AT). The results reveal that hydrogen bonding in different forms plays a significant role in both ion migration and moisture stability for surface passivation.

Enhanced Performance via End-Group Alteration of Benzodithiophene-Based Donors for Organic Solar Cells: a Theoretical Study.

Donor in organic solar cells (OSCs) is essential for promoting charge transport and enhancing photoelectric conversion efficiency. In this work, five new donors M1-M5 were designed by changing the end group to 3-hexyl-2,4-dithiothiazolidine, dicyano-hexylrhodanine, 1,1-dicyanomethylene-3-indanone, 1,3-indenedione and 1,1-dicyano-5,6-difluoroindanone, respectively. The optoelectronic properties of the six donors and their interfacial properties with the well-known acceptor Y6 were studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT).

Revisiting the Enhanced Chemical Reactivity in Water Microdroplets: The Case of a Diels-Alder Reaction.

Often, chemical reactions are markedly accelerated in microdroplets compared with the corresponding bulk phase. While identifying the precise causative factors remains challenging, the interfacial electric field (IEF) and partial solvation are the two widely proposed factors, accounting for the acceleration or turning on of many reactions in microdroplets. In sharp contrast, this combined computational and experimental study demonstrates that these two critical factors have a negligible effect on promoting a model Diels-Alder (DA) reaction between cyclopentadiene and acrylonitrile in water microdroplets.

Designing Benzodithiophene-Based Small Molecule Donors for Organic Solar Cells by Regulation of Halogenation Effects.

The donors are key components of organic solar cells (OSCs) and play crucial roles in their photovoltaic performance. Herein, we designed two new donors (BTR-γ-Cl and BTR-γ-F) by finely optimizing small molecule donors (BTR-Cl and BTR-F) with a high performance. The optoelectronic properties of the four donors and their interfacial properties with the well-known acceptor Y6 were studied by density functional theory and time-dependent density functional theory.

Theoretical Understanding on the Facilitated Photoisomerization of a Carbonyl Supported Borane System.

Boron compound BOMes containing an internal B-O bond undergoes highly efficient photoisomerization, followed by sequential structural transformations, resulting in a rare eight-membered B, O-heterocycle (S. Wang, et al. Org.

A moderate intensity ligand works best: a theoretical study on passivation effects of pyridine-based molecules for perovskite solar cells.

Improving battery stability while maintaining high photoelectric conversion efficiency remains the bottleneck in the current development of perovskite solar cells (PSCs). Three π-conjugated pyridine-based molecules, pyridine (Py), bipyridine (Bpy), and terpyridine (Tpy), were adopted to passivate the PSCs in recent experiments (J. Chen, S.

Cooperative multiple interactions of donor-π-acceptor dyes enhance the efficiency and stability of perovskite solar cells.

Surface passivation by organic dyes has been an effective strategy for simultaneous enhancement of the efficiency and stability of perovskite solar cells. However, lack of in-depth understanding of how subtle structural changes in dyes leads to distinctly different passivation effects is a challenge for screening effective passivation molecules (PMs). In an experiment done by Han (, 2019, , 1803766), three donor-π-acceptor (D-π-A) dyes (SP1, SP2, and SP3) with distinct electron donors have been applied to passivate the perovskite surface, where the efficiency and stability of PSCs are quite different.

A theoretical study on the photochemical generation of phenylborylene from phenyldiazidoborane.

Organic borylenes are a kind of highly reactive species, which play important roles in a lot of reactions as vigorous intermediates. In this work, we investigated the photochemical generation mechanisms of phenylborylene (PhB) together with the side product -phenylnitrenoiminoborane (PhNBN) from phenyldiazidoborane (PhBN) by extrusion of dinitrogen in the two lowest electronic singlet states (S and S) based on the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combined with time-dependent density functional theory (TD-DFT) calculations. Our results show that the reaction PhBN → PhB + 3N involves stepwise N extrusion three times and the azido region rearrangement.

Incorporation of a Boron-Nitrogen Covalent Bond Improves the Charge-Transport and Charge-Transfer Characteristics of Organoboron Small-Molecule Acceptors for Organic Solar Cells.

An organoboron small-molecular acceptor (OSMA) M containing a boron-nitrogen coordination bond (B←N) exhibits good light absorption in organic solar cells (OSCs). In this work, based on M, OSMA M, with the incorporation of a boron-nitrogen covalent bond (B-N), was designed. We have systematically investigated the charge-transport properties and interfacial charge-transfer characteristics of M, along with M, using the density functional theory (DFT) and the time-dependent density functional theory (TD-DFT).

Atomistic Mechanism of Surface-Defect Passivation: Toward Stable and Efficient Perovskite Solar Cells.

Molecular engineering has been demonstrated to be a predominant strategy for augmenting the long-term stability and passivating adverse defects for perovskite solar cells (PSCs). Here, using density functional theory calculations combined with molecular dynamics (AIMD) simulations, the passivation effects of bidentate passivation molecules, and , on the iodine vacancy MAPbI were comprehensively investigated. We demonstrate that engenders stronger adsorption and localized charges on Pb atoms because the separated binding sites match with the MAPbI lattice.

Understanding of Photo-Induced Reversible Rearrangement from Borepin to Borirane.

The first reversible photoisomerization between a borepin and a borirane was reported in the photo-induced reactions of B(npy)Ar (npy=2-(naphthalen-1-yl) pyridine, Ar=phenyl or electron rich aryl; S. Wang, et al. Angew.

Theoretical insights into photo-induced isomerization mechanisms of phenylsulfinyl radical PhSO˙.

Sulfinyl radicals (R-SO˙) play important roles in lots of reactions, while the isomer oxathiyl radicals (R-OS˙) and the isomerization between them are rarely observed due to the poor stability of R-OS˙. In this work, the complete active space self-consistent field (CASSCF) and its multi-state second order perturbation (MS-CASPT2) methods were employed to study the photo-induced reaction mechanisms of phenylsulfinyl radical PhSO˙ 1 and its isomer phenoxathiyl radical PhOS˙ 2. Our results show that 1 and 2 have similar singly occupied molecular orbitals in the ground state but different properties in the excited state, which determine their diverse behaviors after irradiation.

Theoretical Study of Non-Fullerene Acceptors Using End-Capped Groups with Different Electron-Withdrawing Abilities toward Efficient Organic Solar Cells.

Acceptors in organic solar cells (OSCs) are of paramount importance. On the basis of the well-known non-fullerene acceptor Y6, six acceptors (Y6-COH, Y6-COOH, Y6-CN, Y6-SOH, Y6-CF, and Y6-NO) were designed by end-capped manipulation. The effects of end-capped engineering on electronic properties, optical properties, and interfacial charge-transfer states were systematically studied by density functional theory, time-dependent density functional theory, and molecular dynamics.

Theoretical design of asymmetric A-DA'D-A type non-fullerene acceptors for organic solar cells.

The acceptor in organic solar cells (OSCs) is of paramount importance for achieving a high photovoltaic performance. Based on the well-known non-fullerene acceptor Y6, we designed a set of asymmetric A-D1A'D2-A type new acceptors Y6-C, Y6-N, Y6-O, Y6-Se, and Y6-Si by substituting the two S atoms of one thieno[3,2-b]thiophene unit with C, N, O, Se, and Si atoms, respectively. The electronic, optical, and crystal properties of Y6 and the designed acceptors, as well as the interfacial charge-transfer (CT) mechanisms between the donor PM6 and the investigated acceptors have been systematically studied.

Theoretical study on the photochemistry of furoylazides: Curtius rearrangement and subsequent reactions.

Organic azides are an efficient source of nitrenes, which serve as vigorous intermediates in many useful organic reactions. In this work, the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods were employed to study the photochemistry of 2-furoylazide 1 and 3-furoylazide 5, including the Curtius rearrangement to two furylisocyanates (3 and 7) and subsequent reactions to the final product cyanoacrolein 9. Our calculations show that the photoinduced Curtius rearrangement of the two furoylazides takes place through similar stepwise mechanisms via two bistable furoylnitrenes 2 and 6.

End-capped group manipulation of indacenodithienothiophene-based non-fullerene small molecule acceptors for efficient organic solar cells.

As the key component of organic solar cells (OSCs), the acceptor plays key roles in determining the power conversion efficiency (PCE). Based on the famous non-fullerene acceptor ITIC, a series of acceptors (A1-A5) were designed by introducing fused-ring units (phenanthrene, pyrene, benzopyrazine, dibenzo[a,c]phenazine, and phenanthro[4,5-abc]phenazine) as the end groups. Theoretical calculations showed that A1-A5 display improved solubility and redshifted absorption spectra compared with ITIC.

Molecular Engineering of Hexaazatriphenylene Derivatives toward More Efficient Electron-Transporting Materials for Inverted Perovskite Solar Cells.

The electron-transporting material (ETM) in inverted perovskite solar cells (PSCs) plays important role in reducing hysteresis and realizing simple processing procedures, while the improvement of power conversion efficiency is limited by low electron mobility and weak perovskite/ETM interface interaction. In this work, three new ETMs (HAT-1, HAT-2, and HAT-3) were designed by introducing methoxyphenyl, imide, and naphthalene groups into the hexaazatriphenylene (HAT) skeleton, based on the ETM HATNASOC7 synthesized experimentally [Jen; 2016, 55, 8999]. Theoretical calculations showed that the electron mobilities of HAT-1, HAT-2, and HAT-3 are 2.

Theoretical Study on Photoisomerization Mechanisms of Diphenyl-Substituted N,C-Chelate Organoboron Compounds.

N,C-chelate organoboron compounds are widely employed as photoresponsive and optoelectronic materials due to their efficient photochromic reactivity. It was found in experiments that two diphenyl-substituted organoboron compounds, namely B(ppy)Ph (ppy=2-phenylpyridyl) and B(iba)Ph (iba=N-isopropylbenzylideneamine), show distinct photochemical reactivity. B(ppy)Ph is inert on irradiation, whereas B(iba)Ph undergoes photoinduced transformations, yielding BN-cyclohepta-1,3,5-triene via a borirane intermediate.

Insights into the Photoinduced Isomerization Mechanisms of a N,C-Chelate Organoboron Compound: A Theoretical Study.

As the first discovered organoboron compound with photochromic property, B(ppy)Mes (ppy=2-phenylpyridine, Mes=mesityl) displays rich photochemistry that constitutes a solid foundation for wide applications in optoelectronic fields. In this work, we investigated the B(ppy)Mes to borirane isomerization mechanisms in the three lowest electronic states (S , S , and T ) based on the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combined with time-dependent density functional theory (TD-DFT) calculations. Our results show that the photoisomerization in the S state is dominant, which is initiated by the cleavage of the B-C bond.

A Two-Dimensional Spin-Crossover Coordination Polymer Exhibiting Interlayer Multiple C-H···H-B Dihydrogen Bonds.

The reaction of 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethene (tppe) with [Fe(NCBH)] produced a two-dimensional coordination polymer [Fe(NCBH)(tppe)] (), which was pillared in an ABAB manner through interlayer multiple [C-H···H-B] dihydrogen bonds (DHBs) to form a stable porous three-dimensional (3D) supramolecular structure that showed guest-molecule-dependent spin-crossover behaviors.

Nitrogen substitution improves the mobility and stability of electron transport materials for inverted perovskite solar cells.

A suitable electron transport material (ETM) plays key roles in efficient perovskite solar cells (PSCs), because it is beneficial for exciton dissociation and charge transport at the interface thus increasing the short circuit current density. Based on the experimentally reported efficient electron transport molecule 10,14-bis(5-(2-ethylhexyl)thiophen-2-yl)-dipyrido[3,2-a:2',3'-c][1,2,5]thiadiazolo[3,4-i]phenazine (TDTP), we theoretically design a set of new ETMs (TDTP-1, TDTP-2a, TDTP-2b, TDTP-3a, and TDTP-3b) by introducing a nitrogen atom into the thiophene ring or replacing a hydrogen atom on the methyl with an amino group. Quantum-chemical calculations reveal that the designed molecules behave much better than TDTP in terms of electron mobility, air stability, and solubility, where the electron mobility of TDTP-3b is two orders of magnitude higher than that of TDTP owing to the extra SN interactions in TDTP-3b that lead to the quasi two-dimensional π packing motif which facilitates electron transport evidently.

Effect of π-bridge units on properties of A-π-D-π-A-type nonfullerene acceptors for organic solar cells.

Acceptor-π-donor-π-acceptor (A-π-D-π-A)-types of small molecules are very promising nonfullerene acceptors to overcome the drawbacks of fullerene derivatives such as the weak absorption ability and electronic adjustability. However, only few attempts have been made to develop π-bridge units to construct highly efficient acceptors in OSCs. Herein, taking the reported acceptor P1 as a reference, five small-structured acceptors (P2, P3, P4, P5, and P6) have been designed via the replacement of the π-bridge unit.

Photochemical Generation of Chiral N,B,X-Heterocycles by Heteroaromatic C-X Bond Scission (X=S, O) and Boron Insertion.

Chiral organoboron compounds with a chelate backbone and mesityl/heterocycle substituents (thienyl, furyl, and derivatives thereof) undergo a quantitative phototransformation that yields rare, chiral N,B,X-containing heterocycles, such as base-stabilized 1,2-thiaborinines and 1,2-oxaborinines. Boriranes were observed as intermediates in some of these transformations. The oxaborinines display further reactivity, generating 4a,12b-dihydrobenzo[h][1,2]oxaborinino[4,3-f]quinolines through a sequential conrotatory electrocyclization and a [1,5]-H shift.