Dual‐Functional Surface Engineering of ZnO Nanocrystals via Boronic Acid Anchoring for 20.53%‐Efficiency Conventional Organic Solar Cells with Enhanced Stability

Zinc oxide (ZnO) nanocrystals synthesized via alcoholysis are widely employed as electron transport layers (ETLs) in conventional organic solar cells (OSCs) due to their low-temperature processability. However, the high surface-to-volume ratio of colloidal ZnO nanocrystals introduces abundant undercoordinated Zn atoms and polar hydroxyl groups, which act as charge recombination centers and render the device susceptible to moisture ingress, critically limiting efficiency and stability. Herein, we report a dual-functional surface modification strategy using 3,5-di-tert-butylphenylboronic acid (DBA) as a capping ligand for ZnO nanocrystals. The boronic acid moiety chemically displaces reactive surface hydroxyl groups and coordinates with undercoordinated Zn sites, eliminating interfacial trap states. Meanwhile, the hydrophobic tert-butyl termini assemble into a compact shielding layer that suppresses moisture and oxygen permeation from the top electrode side. Consequently, DBA-modified ZnO ETLs deliver a power conversion efficiency of 20.53% in D18:L8-BO:BTP-eC9-based conventional OSCs, significantly outperforming pristine ZnO-based devices (18.88%). More importantly, all the storage-, thermal-, and illumination stabilities of the OSCs are substantially enhanced. This work establishes boronic acid-based ligand exchange as an effective strategy for simultaneously passivating surface defects and imparting hydrophobic shielding to ZnO ETLs in conventional OSCs.