Toward a Robust ZnO Interface via Fullerene‐Based SAMs: Defect Passivation and Compatibility Tuning for High‐Performance Inverted Organic Solar Cells

Why It Matters

By stabilizing the ZnO interface and enhancing charge extraction, these SAMs push inverted organic solar cells toward commercial viability, offering both higher efficiency and longer operational lifetimes.

Key Takeaways

• Fullerene SAMs improve ZnO surface passivation
• 4EG-PA yields denser monolayer than C2-PA
• Devices achieve 19.46% efficiency, 84% after 2000h
• Charge‑transfer states accelerate electron extraction, reduce recombination
• SAM buffer enhances active‑layer compatibility, prevents reaggregation

Pulse Analysis

Inverted organic solar cells rely on zinc oxide as a low‑cost electron‑transport layer, yet ZnO’s polar surface often triggers trap formation and chemical instability. Recent advances in molecular engineering have turned self‑assembled monolayers into a versatile tool for tailoring interfacial chemistry. Fullerene‑based SAMs combine strong electron affinity with customizable linkers, allowing researchers to simultaneously passivate surface defects, tune work function, and create a protective barrier that mitigates photocatalytic degradation. This multifunctional approach addresses two of the most persistent loss mechanisms in organic photovoltaics: charge recombination and interlayer delamination.

The comparative study of C2‑PA and 4EG‑PA highlights how linker chemistry dictates monolayer morphology and electronic coupling. The ethylene‑glycol chain in 4EG‑PA promotes tighter packing, which not only reduces surface roughness but also facilitates the formation of interfacial charge‑transfer (CT) states observed via transient absorption spectroscopy. These CT states act as a bridge for electrons, lowering the energetic barrier for extraction while concurrently improving hole transfer from acceptor to donor molecules. The net effect is a measurable increase in short‑circuit current and a suppression of non‑geminate recombination pathways, translating into record‑high efficiencies for ZnO‑based inverted devices.

Beyond the laboratory, the demonstrated stability—84% performance retention after 2,000 hours—signals a viable route toward scalable production. The dense SAM layer serves as a universal compatibility buffer, allowing diverse active‑layer formulations to be integrated without risking reaggregation or morphological degradation. This strategy can be extended to other emerging thin‑film technologies, such as perovskite and quantum‑dot photovoltaics, where interface engineering remains a bottleneck. As the solar industry seeks cost‑effective, high‑performance solutions, fullerene‑based SAMs offer a pragmatic pathway to reconcile efficiency, durability, and manufacturability.