Resolving Atomic-Scale Interactions in Nonfullerene Acceptor Organic Solar Cells with Solid-State NMR Spectroscopy,...

Area of Science:

• Materials Science
• Organic Electronics
• Solid-State Physics

Background:

• Fused-ring core nonfullerene acceptors (NFAs), particularly the Y-series, have significantly advanced organic solar cell (OSC) power conversion efficiency (PCE) beyond 18%.
• Despite high PCEs, the molecular-level origins of performance variations (5% to 18% PCE) in systems like PM6:Y6 OSCs remain unclear.

Purpose of the Study:

• To elucidate the atomic-scale interactions governing the morphology and performance of Y6-based organic solar cells.
• To understand how molecular packing and sidechain orientation in Y6 influence bulk heterojunction (BHJ) morphology and PCE.

Main Methods:

• Utilized a combined approach of solid-state Nuclear Magnetic Resonance (NMR) spectroscopy, crystallography, and molecular modeling.
• Investigated Y6 in neat crystals, thin films, and PM6:Y6 BHJ blends.

Main Results:

• Y6 morphology in BHJ blends is independent of neat film or single crystal morphology.
• Solvent processing dictates self-assembled structures and morphologies in PM6:Y6 blends.
• Relative orientation of Y6 sidechains and end groups to the fused-ring core critically impacts BHJ morphology and solar cell performance.

Conclusions:

• Molecular-level understanding of BHJ formation is achieved through combined experimental and computational methods.
• Sidechain and end-group engineering in NFAs is crucial for optimizing morphology and enhancing PCE in organic solar cells.
• This approach provides a roadmap for designing more efficient and stable next-generation NFAs for OSCs.