There are a few reports that the optoelectronic properties of the methoxyaniline-based hole-transporting materials are intimately correlated with the positions of −OMe substituents. To dig into this phenomenon deeply, we theoretically design five new hole-transporting materials (HTMs) based on 2′,7′-bis(bis(4-methoxyphenyl)amino)spiro[cyclopenta[2,1-b:3,4-b′]dithiophene-4,9′-fluorene] (FDT) through altering the positions of −OMe substituents. Then, the electronic structures, optical properties, and hole-transporting properties are investigated at the molecular level via density functional theory and Marcus theory coupled to Einstein relation. The calculated results reveal that the derivatives with o-OMe or m-OMe substituent exhibit lower HOMO levels, favoring higher open-circuit voltages. Most importantly, benefitting from greater order and compact intermolecular stacking, the derivatives with o-OMe substituents (F1, F3) as HTMs exhibit relatively decent hole mobilities (F1: 6.29 × 10–2 cm2 V–1 s–1; F3: 2.49 × 10–3 cm2 V–1 s–1), which are two or three orders of magnitude higher than that of FDT. Quantum chemistry calculation and crystal packing arrangement simulation indicate that −OMe substituents at different positions show disparate orientations and thus affect the molecular stacking. Our work reiterates the importance of molecular configuration for the materials properties and provides those who are engaged in upgrading the performances of hole-transporting materials a new train of thought and tactics with ease and economy.
Thiophene-bridged and thiazole-bridged diketopyrrolopyrrole (DPP) polymers for near-infrared (near-IR) photovoltaic applications have been investigated via density functional theory (DFT) and Marcus charge transfer theory. Compared with thiophene-bridged DPP polymers, thiazole-bridged polymers have higher ionization potentials (IPs) but poorer optical absorption and worse charge transport capability. Different beneficial substituents replaced the hydrogen atoms (H) on the thiazole rings for the sake of reversing the disadvantages of thiazole-bridged DPP polymers and making these compounds better near-infrared absorbing materials. In order to gain deep insight into the impact of π-bridge modification on the photoelectronic properties of DPP polymers, their electronic structures, absorption capabilities, intramolecular charge transfer properties and charge transport performances have been analyzed. The calculated results reveal that π-bridge modification is a feasible way to improve the light-absorbing capability, electron excitation properties and charge transport performance of thiazole-bridged DPP polymers. It is expected that π-bridge modification can also work for other polymers containing π-bridge units. We hope that our research efforts will be helpful in the designing of new near-IR absorbing materials and could motivate further improvement of organic solar cells.
The construction of state‐of‐the‐art charge transporting materials (CTMs) is challenging in modulating molecular configurations for simultaneously achieving high thermal stability and appreciable solution processability. Herein, N,N′‐bis(1‐indanyl)naphthalene‐1,4,5,8‐tetracarboxylic diimide (NDI‐ID) is served as a theoretical model to investigate the influence of molecular structure on the tradeoff between thermal stability and solubility. Compared with the alkyl substituted analog, the thermal stability of NDI‐ID is enhanced by the intramolecular and intermolecular short contacts, indicating the conformational rigidity dictates the morphological stability of the film phase. On the other hand, the dynamic topological transformation of material molecules occurs during the solvation process and, where the intramolecular hydrogen bonds are attenuated by the interactions with the surrounding solvent, leads to the increased solubility. The meta‐stable molecular configuration endows NDI‐ID a favorable union of superior solution processability and higher thermal stability, and this insight is also perfectly exemplified by the newly designed CTMs. Therefore, these results reveal the significant role of structural dynamics on material properties, which can provide a new train of thought to develop CTMs for highly efficient and stable perovskite solar cells.
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