Achieving 20.5% Efficiency in Organic Solar Cells via Co-Crystallizable Small Molecule Acceptors

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Ternary strategies in organic solar cells (OSCs) improve efficiency but lack molecular-level understanding of electronic coupling and energetic alignment.
• Developing new materials and strategies is crucial for advancing OSC performance.

Purpose of the Study:

• To investigate the formation of a bimolecular co-crystal (BC) between a known acceptor (L8-BO) and a new guest molecule (Y18-C3).
• To understand the role of intermolecular electronic coupling in tuning energetic alignment and absorption profiles.
• To evaluate the performance and composition tolerance of OSCs utilizing this BC strategy.

Main Methods:

• Single-crystal X-ray diffraction analysis to confirm the bimolecular co-crystal structure.
• Fabrication and characterization of D18:L8-BO:Y18-C3 based organic solar cells.
• Performance evaluation including power conversion efficiency, short-circuit current, fill factor, and open-circuit voltage.

Main Results:

• A well-defined bimolecular co-crystal (BC) was formed between L8-BO and Y18-C3, confirmed by X-ray diffraction.
• Strong intermolecular electronic coupling was achieved, enabling tunable energetic alignment and absorption.
• OSC devices achieved a high power conversion efficiency of 20.50% with enhanced molecular ordering and suppressed charge recombination.
• High performance (>19.6%) was maintained even with 50% Y18-C3 content, demonstrating high composition tolerance.

Conclusions:

• Constructing a BC with a shared conjugated backbone and compatible intermolecular interactions is an effective molecular design principle for high-performance OSCs.
• This strategy leads to enhanced molecular ordering, tunable electronic properties, and suppressed charge recombination.
• The developed BC approach offers a pathway to highly efficient and composition-tolerant organic solar cells.