Manipulating Alkyl Inner Side Chain of Acceptor for Efficient As-Cast Organic Solar Cells

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• As-cast organic solar cells (OSCs) offer a promising route for low-cost renewable energy generation.
• Optimizing morphology and energy levels in OSCs is crucial for enhancing device efficiency.

Purpose of the Study:

• To design and synthesize novel small-molecule acceptors (A1-A5) with tailored alkyl side chains.
• To investigate the impact of alkyl chain extension on film morphology and device performance in as-cast OSCs.
• To establish a strategy for controlling intermolecular interactions and film formation for high-performance OSCs.

Main Methods:

• Synthesis of five small-molecule acceptors (A1-A5) with varying alkyl side chain lengths.
• Characterization of film properties including absorption spectra and energy levels.
• In situ techniques to study film formation dynamics and molecular assembly.
• Fabrication and performance testing of as-cast OSC devices.

Main Results:

• Alkyl chain extension led to blue-shifted absorption spectra and slightly higher LUMO levels.
• Increased alkyl chain length improved acceptor-donor compatibility, promoting donor phase formation.
• Enhanced film morphology with favorable fibrillar structure, molecular stacking, and vertical phase separation.
• Incremental improvements in fill factor observed from A1 to A5 based devices.
• A3-based as-cast OSCs achieved a record power conversion efficiency of 18.29%.

Conclusions:

• Tailoring alkyl side chains on pyrrole motifs is an effective strategy for optimizing OSC performance.
• Controlling intermolecular interactions and film formation dynamics is key to high-efficiency as-cast devices.
• The developed acceptors and strategy pave the way for commercially viable, low-cost organic solar cells.