Copolymerized Plasticizer Enables Halogen-Free Processing Toward 20.78% and 17.83% Efficient Organic Solar Cells and...

Area of Science:

• Materials Science
• Organic Electronics
• Polymer Chemistry

Background:

• Nonhalogenated solvents are ideal for scalable organic solar cell (OSC) fabrication.
• High-molecular-weight donor polymers with crystalline backbones exhibit poor solubility in these solvents, hindering OSC performance.
• The pinnacle donor material (D18) exemplifies this challenge, limiting morphology development.

Purpose of the Study:

• To enhance the solubility and processability of high-molecular-weight donor polymers in nonhalogenated solvents.
• To improve the morphology evolution and device performance of organic solar cells (OSCs).
• To develop a strategy that maintains the polymer's intrinsic properties while improving solvation.

Main Methods:

• A copolymerized "plasticizer" strategy was employed, integrating a specific plasticizing comonomer into the D18 polymer backbone, creating D18-O.
• The plasticizing unit (bis(2-(2-methoxyethoxy)ethyl) thieno[3,2-b]thiophene-3,6-dicarboxylate) was designed to enhance dipolar interactions with toluene.
• The effects of this modification on polymer solubility, aggregation, crystallization kinetics, and morphology were investigated.

Main Results:

• D18-O demonstrated significantly enhanced solubility in toluene due to improved solvation via dipolar interactions.
• The plasticizing units effectively suppressed excessive pre-aggregation and slowed down donor crystallization kinetics.
• This led to the formation of well-defined nanocrystals and optimized hierarchical morphologies during nonhalogenated processing.

Conclusions:

• The copolymerized plasticizer strategy successfully overcomes the solubility limitations of high-performance donor polymers in nonhalogenated solvents.
• This approach enables high power conversion efficiencies (PCEs) in organic solar cells (OSCs) and modules processed from toluene.
• Record certified PCEs of 20.40% for OSCs and 17.29% for modules were achieved, alongside exceptional stability.