Design of Intrinsically Stable Hole-Selective Self-Assembled Monolayers by Introducing Fused-Ring Intramolecular...

Hole-selective self-assembled monolayers (SAMs) incorporating electron-donating conjugated units as head groups have witnessed remarkable success in helping achieve high-performance organic solar cells (OSCs). However, these molecules frequently exhibit a shallow lowest unoccupied molecular orbital (LUMO) level, rendering them prone to photodegradation. To tackle this problem, we introduce fused-ring intramolecular donor-acceptor (D-A) interactions into the design of SAM molecules to downshift the LUMO level. The resultant molecule, JJ32, shows both enhanced photostability and intermolecular interactions. Furthermore, the fused-ring intramolecular D-A interactions also help stabilize the radical cation state of JJ32 to result in significantly improved redox stability. This enables them to be included in polyoxometalate (POM)-based composite hole-selective layers (HSLs), resulting in an impressive efficiency of 19.85% alongside significantly enhanced stability in corresponding OSCs. This study not only validates the concept of using fused-ring D-A-structure SAMs to improve the efficiency and stability of OSCs but also elucidates the relationship between SAM structures and POM doping behaviors to provide an effective strategy in designing intrinsically stable SAM molecules for high-performance OSCs.