Synergistic Interplay between Asymmetric Backbone Conformation, Molecular Aggregation, and Charge-Carrier Dynamics in Fused-Ring Electron Acceptor-Based Bulk Heterojunction Solar Cells
Xin Song, Licheng Hou, Renjun Guo, Qi Wei, Linqiang Yang, Xinyu Jiang, Suo Tu, Ao Zhang, Zhipeng Kan, Weihua Tang, Guichuan Xing, Peter Müller‐Buschbaum
Abstract
Asymmetric fused-ring electron acceptors (a-FREAs) have proved to be a promising type of electron acceptor for high-performance organic solar cells (OSCs). However, the relationship among molecular structures of a-FREAs and their nanoscale morphology, charge-carrier dynamics, and device performance remains unclear. In this contribution, two FREAs differing in conjugated backbone geometry with an asymmetric conformation (IPT-2F) or symmetric one (INPIC-2F) are selected to systematically explore the superiorities of the asymmetric conformation. Despite the frailer extinction coefficient and weaker crystallinity, IPT-2F shows stronger dipole interactions in the asymmetrical backbone, which would induce a closer lamellar packing than that of the symmetrical counterpart. Using PBDB-T as the electron donor, the IPT-2F-based OSCs achieve the best power conversion efficiency of 14.0%, which is ca. 67% improvement compared to the INPIC-2F-based ones (8.37%), resulting from a simultaneously increased short-circuited current density (Jsc) and fill factor. Systematical investigations on optoelectronic and morphological properties show that the asymmetric conformation-structured IPT-2F exhibits better miscibility with the polymer donor to induce a favorable blend ordering with small domain sizes and suitable phase separation compared to the INPIC-2F symmetric molecule. This facilitates an efficient charge generation and transport, inhibits charge-carrier recombination, and promotes valid charge extraction in IPT-2F-based devices.