Polymer Solar Cells: Solubility Controls Fiber Network Formation

Area of Science:

• Materials Science
• Polymer Chemistry
• Renewable Energy

Background:

• Polymer solar cells rely on nanoscale morphology for performance.
• Controlling polymer-fullerene domain size during drying is crucial but poorly understood.

Purpose of the Study:

• Investigate morphology formation in polymer solar cells.
• Understand factors governing polymer fiber width and its effect on performance.

Main Methods:

• Studied an alternating copolymer (PDPPTPT) with [6,6]-phenyl-C71-butyric acid methyl ester.
• Analyzed fiber width using transmission electron microscopy.
• Developed a ternary solvent system to tune fiber width.

Main Results:

• Polymer fiber width is mainly determined by polymer solubility and molecular weight.
• Higher molecular weight leads to lower solubility and smaller fiber width.
• Fiber width inversely correlates with photocurrent; smaller fibers yield higher photocurrent.

Conclusions:

• Polymer fiber width is governed by nucleation, driven by polymer solubility, not a frozen dynamical state.
• Ternary solvent systems can tune fiber width for improved solar cell performance.
• Results provide a model for morphology control in polymer solar cells.