Differently Linked Perylene Bisimide Dimers with Various Twisting and Phase Structures for Nonfullerene All-Small-Molecule Organic Solar Cells

Nonfullerene all-small-molecule organic solar cells (NF all-SMSCs) are an important classification in the organic solar cell system. However, the application and research of NF all-SMSCs are limited due to the easy aggregation of small molecules to form large-phase domains. Perylene bisimides (PBIs) have been widely used as nonfullerene acceptors. Simply changing the link position of the PBI dimer can control the accumulation of molecules to regulate the size of the phase domain. Herein, the bay-linked, ortho-linked, and hydrazine-linked PBI dimers as nonfullerene acceptors, named as B-SdiPBI, O-SdiPBI, and H-SdiPBI, respectively, were chosen. The link position of the PBI dimer can lead to diverse molecular torsion and planarity, which affects the film-forming ability, phase separation, and thus optoelectronic properties. NF all-SMSCs based on B-SdiPBI, O-SdiPBI, and H-SdiPBI as nonfullerene acceptors and a small molecule DR3TBDTT as the donor achieve the best power conversion efficiencies of 1.93, 3.30, and 4.05%, respectively. The result is consistent with the sequence of inter-PBI twist and phase domain size of the corresponding blend films in the device. The DR3TBDTT:H-SdiPBI system has the best efficiency with the largest dihedral angle of H-SdiPBI (psi = 90 degrees) and an appropriate phase size (10-40 nm), whereas the smaller dihedral angle of O-SdiPBI (psi = 86 degrees) produces a larger phase size (20-50 nm) and the smallest dihedral angle of B-SdiPBI (psi = 71 degrees) gives the largest phase size (30-80 nm). This illustrates that the twist angle can effectively increase the phase separation between the acceptor and donor to obtain an effective phase size in this system. The work provides a guide for designing the acceptors and controlling phase domains of high-performance NF all-SMSCs.