How the Connectivity of Methoxy Substituents Influences the Photovoltaic Properties of Dissymmetric Core Materials: A Theoretical Study on FDT

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 [cydopenta[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 X 10(-2) cm(2) V-1 s(-1); F3: 2.49 X 10(-3) cm(2) 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.