Dispersion effect of chlorination induced intermolecular stacking optimization of small-molecule acceptor for high-performance organic solar cells

Abstract

It is recognized that the introduction of chlorine substituent facilitates improving intermolecular interaction, while its intrinsic mechanism is still underexploited. This work demonstrates the significance of polarizable dispersion effect of chlorine substituent in optimizing the intermolecular π-π stacking of small-molecule acceptor. It is demonstrated that chlorination conducted on small molecule can enhance the polarizability along the direction parallel to the conjugated backbone, favoring dispersion-dominated molecular face-to-face packing. As a result, the chlorinated derivatives QX-Cl and QX-2Cl demonstrate more than two times higher electron mobility compared to that of chlorine-free analogue QX. On the other hand, the monochlorination conducted on QX molecule effectively improve the J-aggregation characteristic, resulting in the highest extinction coefficient among the three analogues. Therefore, the D18:QX-Cl-based device yielded a power-conversion efficiency (PCE) of 19.53%, with an exceptional fill factor (FF) of 82.88%, which is higher than that of the device based on D18:QX (PCE = 18.28%, FF = 79.91%). By using QX-Cl as a guest acceptor for D18:N3 system to optimize molecular packing and phase separation morphology, the ternary device demonstrates a notable PCE of 20.41%, which is a significant improvement with regard to the PCE of 19.12% for the D18:N3-based binary device.