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. © 2024 Wiley-VCH GmbH.