Inner Side Chain Modification of Small Molecule Acceptors Enables Lower Energy Loss and High Efficiency of Organic Solar Cells Processed with Non‐halogenated Solvents

Organic solar cells (OSCs) processed with non‐halogenated solvents usually suffer from excessive self‐aggregation of small molecule acceptors (SMAs), severe phase separation and higher energy loss (Eloss), leading to reduced open‐circuit voltage (Voc) and power conversion efficiency (PCE). Here, we designed and synthesized two SMAs L8‐PhF and L8‐PhMe by introducing different substituents (fluorine for L8‐PhF and methyl for L8‐PhMe) on the phenyl end group of inner side chains of L8‐Ph, and investigated the effect of the substituents on the intermolecular interaction of SMAs, Eloss and performance of OSCs processed with non‐halogenated solvents. It is found that compared with L8‐PhF, which possesses strong intermolecular interactions but downgraded molecular packing order, L8‐PhMe exhibits more effective non‐covalent interactions, which improves the tightness and order of molecular packing. When blending the SMAs with PM6, the OSCs based on L8‐PhMe shows reduced non‐radiative energy loss, and enhanced Voc than the devices based on the other two SMAs. Consequently, the L8‐PhMe based device processed with o‐xylene and using 2PACz as the hole transport layer shows an outstanding PCE of 19.27%. This study highlights that the Eloss of OSCs processed with non‐halogenated solvents could be decreased through regulating the intermolecular interactions of SMAs by inner side chain modification.