All-small-molecule organic solar cells with over 14% efficiency by optimizing hierarchical morphologies

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• High-efficiency organic solar cells (OSCs) rely on optimized morphology in their bulk heterojunction (BHJ) active layers.
• Achieving high performance in all-small-molecule OSCs (all-SM OSCs) requires careful molecular design and morphological control.

Purpose of the Study:

• To design and synthesize a novel small-molecule donor for high-efficiency all-SM OSCs.
• To investigate the relationship between molecular structure, hierarchical morphology, and photovoltaic performance in BHJ active layers.
• To achieve a record power conversion efficiency (PCE) for binary all-SM OSCs.

Main Methods:

• Single-crystal structural analysis to determine molecular planarity and packing.
• Synthesis of a narrow bandgap small-molecule acceptor with an absorption edge >930 nm.
• Optimization of BHJ hierarchical morphologies through careful processing.
• Fabrication and characterization of all-SM OSC devices.

Main Results:

• A novel small-molecule donor with planar structure and compact intermolecular packing was synthesized.
• Binary all-SM OSCs achieved a record power conversion efficiency (PCE) of 14.34%.
• Hierarchical morphologies with coexisting donor/acceptor-rich domains (up to 70 nm) and nanoscale donor crystals were observed.
• The optimized morphology demonstrated a synergistic effect between molecular packing and domain structure.

Conclusions:

• The designed small-molecule donor and optimized hierarchical morphology are crucial for high-performance all-SM OSCs.
• This study provides insights into structure-property relationships in BHJ active layers for organic photovoltaics.
• The developed all-SM photovoltaic system shows significant promise for future high-efficiency OSC applications.