The crucial role of intermolecular π–π interactions in A–D–A-type electron acceptors and their effective modulation

Here, the crucial role of intermolecular π–π interactions in A–D–A-type acceptors is examined and a simple yet effective modulation method is presented. By side chain manipulation, two small molecule acceptors, IDT-C6 and IDT-PhC6, are designed and synthesized with different crystalline morphologies. Since n-hexyl side chains have less steric hindrance than hexylphenyl side chains, IDT-C6 exhibits enhanced intermolecular π–π interactions relative to IDT-PhC6. Benefiting from the improved charge transport properties of the IDT-C6-based device, a high PCE of 12.5% is recorded, whereas those of the IDT-PhC6-based device delivers a moderate PCE of just 5.6%.