Multi-site Passivation of ZnO Metal Oxides via Biomolecules for Efficient and Highly Stable Organic Solar Cells

ZnO nanoparticles (nps) among metal oxide (MOs) are proven to be essential electron transporting layers (ETLs) applied in organic solar cells (OSCs). However, intrinsic defects, interfacial charge recombination, and catalytic behavior towards the active layer restrict the applications of ZnO nps for efficient and long-term stable OSCs. The commonly available biomolecule cytidine 5'-monophosphate (CMP-OH) with phosphonic acid, its salt cytidine 5'-monophosphate disodium salt (CMP-ONa) with a phosphate group as an anchoring group and conjugated terminal functional in both analogous molecules provide carrier transfer bridge at bottom interface of the active layer. Systematized theoretical investigations and characterizations have discovered the multi-site coordination of CMP-OH towards acceptor molecules and ZnO nps. The dual-side alignment of CMP analogous molecules hinders interfacial charge recombination and enhances charge transfer potential at once. Inevitably, PM6:L8-BO-based OSCs with modified ETL obtain 18.13% efficiency, 12% higher than that of unmodified nps. Besides higher efficiency, CMP-OH-based OSC devices illustrate remarkably improved thermal stability for 500 h at 85 degrees C with 72% of initial PCE and operation stability for 2000 h with 90.1% of initial PCE. This work reveals the passivation mechanism of multi-anchoring groups towards MOs and single-functional groups towards the active layer to optimize the interface for efficient and highly stable OSCs.