BN-Embedded Cycloarenes: One-Pot Borylation Synthesis, Photoelectric Properties, and Application in Perovskite Solar Cells

Abstract

Incorporating heteroatoms, such as nitrogen, oxygen, and/or sulfur atoms, into cycloarenes can effectively regulate their molecular geometries and (opto)electronic properties. However, the rarity of cycloarenes and heterocycloarenes limits the further exploitation of their applications. Herein, we designed and synthesized the first examples of boron and nitrogen (BN)doped cycloarenes (BN-C1 and BN-C2) via one-pot intramolecular electrophilic borylation of imine-based macrocycles. BN-C2 adopts a bowl-shaped conformation, while BN-C1 possesses a planar geometry. Accordingly, the solubility of BN-C2 was significantly improved by replacing two hexagons in BN-C1 with two N-pentagons, due to the creation of distortions away from planarity. Various experiments and theoretical calculations were carried out for heterocycloarenes BN-C1 and BN-C2, demonstrating that the incorporated BN bonds diminish the aromaticity of 1,2-azaborine units and their adjacent benzenoid rings but preserve the dominant aromatic properties of pristine kekulene. Importantly, when two additional electron-rich nitrogen atoms were introduced, the highest occupied molecular orbital energy level of BN-C2 was elaborately lifted compared with that of BN-C1. As a result, the energy-level alignment of BN-C2 with the work function of the anode and the perovskite layer was suitable. Therefore, for the first time, heterocycloarene (BN-C2) was explored as a hole-transporting layer in inverted perovskite solar cell devices, in which the power conversion efficiency reached 14.4%.

Boron- and Nitrogen-Embedded Polycyclic Arenes as an Emerging Class of Organic Semiconductors

“…127 The electron-donor effect of nitrogen and electron affinity of boron endowed 68 with an ambipolar charge trapping property, and the device showed large ambipolar memory windows of 52.18 V (ΔV TH+ = 24.13 V, In 2023, Liu and co-workers reported the synthesis of BNembedded cycloarenes 69 and investigated its applications in inverted perovskite solar cell (IPSC) devices (Figure 16c). 128 A suitable HOMO energy level of −5.29 eV was observed in 69 via the incorporation of quadruple B−N units, which was comparable to the reported highly efficient hole transporting material poly[bis(4phenyl)(2,4,6-trimethylphenyl)amine] (PTAA, −5.16 eV). Consequently, the IPSC devices employing 69 as the hole-transporting layer exhibited a high PCE of up to 14.42%.…”

“…In 2023, Liu and co-workers reported the synthesis of BN-embedded cycloarenes 69 and investigated its applications in inverted perovskite solar cell (IPSC) devices (Figure c) . A suitable HOMO energy level of −5.29 eV was observed in 69 via the incorporation of quadruple B–N units, which was comparable to the reported highly efficient hole transporting material poly­[bis­(4phenyl)­(2,4,6-trimethylphenyl)­amine] (PTAA, −5.16 eV).…”

“…(c) Chemical structure of 69 and the photocurrent density–voltage ( J – V ) curves in the perovskite solar cell devices. Adapted with permission from ref . Copyright 2023 American Chemical Society.…”

Flexible Backbone-Assisted Green-Solvent Processable Polymer Hole Transport Material in Perovskite Solar Cells

“…Unfortunately, these highly toxic solutions have serious ecotoxicological effects such as harmful effects on specific organs in animals and humans. − Therefore, it is worth pursuing persistent efforts toward an implementation of green solvents during the industrial processes in conjunction with the improvement of PCEs. − However, attaining p-HTMs with a fine blend morphology by using green solvents is challenging. This is because, to achieve high hole mobility and produce high-performance PSCs, p-HTMs are designed as conjugated molecules with rigid and planar molecular backbones to promote the intermolecular π–π stacking and facilitate efficient interface charge transport. − Inevitably, the strong interlayer interaction of highly conjugated HTMs compromises their solubility in green solvents. ,− Lacking solubility could result in excessive phase separation and heterogeneous thin films for HTMs, which would sacrifice device performance …”

Impact of isoelectronic substitution on the excited state processes in polycyclic aromatic hydrocarbons: a joint experimental and theoretical study of 4a,8a-azaboranaphthalene

“…19 Therefore, recent years saw increasing interest in understanding the spectroscopy and photochemistry of BN-substituted aromatic molecules. 20–26 A few azaborines have been investigated by IR-spectroscopy in rare gas matrices and by photoionization in the gas phase. 27–29 However, no experiments on the dynamics of excited electronic states have yet been reported and BN-doped PAHs have only been investigated in solution.…”