N‐Type Small Molecule Electron Transport Layers with Excellent Surface Energy and Moisture Resistance Siloxane for Non‐Fullerene Organic Solar Cells

Abstract Electron transport layers (ETLs) generally contain polar groups for enhancing performance and reducing the work function. Nevertheless, the polar group with high surface energy may cause inferior interfacial compatibility, which challenges the ETLs to balance stability and performance. Here, two conjugated small molecules of ETLs with low surface energy siloxane, namely PDI‐Si and PDIN‐Si, are synthesized. The siloxane with low surface energy not only enhances the interfacial compatibility between ETLs and active layers but also improves the moisture‐proof stability of the device. Impressively, the amine‐functionalized PDIN‐Si can simultaneously exhibit conspicuous n‐type self‐doping properties and outstanding moisture‐proof stability. The optimization of interfacial contact and morphology enables the PM6:Y6‐based OSC with PDIN‐Si to achieve a power conversion efficiency (PCE) of 15.87%, which is slightly superior to that of classical ETL PDINO devices (15.27%), and when the PDIN‐Si film thickness reaches 28 nm, the PCE remains at 13.19% (≈83%), which indicates that PDIN‐Si has satisfactory thickness insensitivity to facilitate roll‐to‐roll processing. Excitingly, after 120 h of storage in an environment with humidity above 45%, the unencapsulated device with PDIN‐Si as ETL remains at 75% of the initial PCE value, while the device with PDINO as ETL is only 50%.