Bifunctional Urea–Polyethyleneimine‐Mediated Surface Engineering in SnO2 Electron‐Transport Layer for Efficient and Stable Organic Solar Cells

Abstract

Because of its high conductivity, wide bandgap, and excellent photostability, tin oxide (SnO2) has long been recognized as an electron‐transport layer (ETL) in organic solar cells (OSCs). However, the energy‐level mismatch between the work function (WF) of SnO2 and the lowest unoccupied molecular orbital level of Y‐series nonfullerene acceptors (NFAs), along with the abundance of surface defects on SnO2, have limited its widespread application as ETLs in OSCs. Herein, a novel approach utilizing urea‐functionalized polyethyleneimine (PEI) materials called u‐PEIs for modifying SnO2 is introduced. This modification, which serves dual purposes of WF modulation and surface‐defect passivation, can mitigate the energy barriers of SnO2/Y‐series NFA and increase the conductivity of the SnO2 film. PM6:Y6‐based OSCs with u‐PEI‐modified SnO2 (SnO2:u‐PEI) ETLs exhibit a remarkable efficiency of 16%, which significantly exceeds that (13.5%) achieved with bare SnO2‐based OSCs, along with outstanding photo‐ and thermal stability. This study confirms the efficacy of urea‐functionalized PEI for efficient and stable OCSs, paving the way for SnO2 applications.