Inclusion of Piperidine Side‐Chain in Cathode Interlayer Materials Toward Improved Stability in Organic Solar Cells

Lab-scale Organic solar cells (OSCs) have achieved remarkable progress with state-of-the-art power conversion efficiencies (PCE) exceeding 20%. However, they are still confronted with inadequate device lifetime resulting from instabilities in either material structures or film morphologies of the active layer and interfacial layers. Here, we designed and synthesized a cathode interlayer (CIL) material, NDI-N-P. By replacing the commonly used linear amine side-chain with a cyclic amine, piperidine. The negative effects of the linear amine side-chain on the acceptor in the active layer are largely mitigated via the improved steric hindrance of piperidine. OSC devices based on NDI-N-P achieve a PCE of 19.8% and demonstrate improved long-term stability, showcasing the potential of tailoring the local structure of CILs toward highly efficient and stable OSCs. Furthermore, we tailored the aryl terminal groups to obtain an extra CIL molecule, NDI-I-P, with isoquinolyl side-groups to investigate the influence of electron-withdrawing ability of terminal groups on the self-doping effects within the molecules and the performance of resulting devices. This provides insights for further regulating the photoelectric and aggregate properties of CILs toward enhanced electron extraction in OSCs.