On the study of influence of molecular arrangements and dipole moment on exciton binding energy in solid state

Abstract

AbstractExciton binding energy (Eb) is one of the key factors affecting charge transfer and charge separation in organic solar cells (OSCs). However, most studies on Eb only focus on a single molecule, which is far from the real situation. How molecular arrangements and dipole moment influence Eb in solid state is still an open question. In the present work, a methodology combining the polarizable continuum model with calculated static dielectric constants, optimally tuned long‐range corrected hybrid density functional, and corrected optical gap is proposed for the calculations of Ebs with high accuracy. We have chosen boron subphthalocyanine chloride (subPC) with a strong dipole moment and anthracene without a dipole moment as two representative examples. To simulate solid‐state environmental effects better, different molecular dimers have been built up to simulate molecular arrangements. The most striking finding is that molecular arrangements and dipole moment have evident effects on Ebs. The calculated Ebs of anthracene in dimers are always smaller than that obtained with a single‐molecule model. In contrast, the Ebs of subPC dimers are generally larger (up to 30%) than that of subPC monomer; however, one exception is the convex‐to‐concave dimer configuration with the largest dipole moment, which has a smaller Eb by 5% than the monomer. These findings provide a guideline for the morphology control of thin film to improve the performance of OSC.