Discriminating between bilayer and bulk heterojunction polymer:fullerene solar cells using the external quantum...

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• The morphology of the active layer is critical for polymer:fullerene solar cell performance.
• Understanding morphology control is key to optimizing power conversion efficiency.

Purpose of the Study:

• To compare the morphology and performance of bilayer P3HT/PCBM solar cells with bulk heterojunction (BHJ) P3HT:PCBM solar cells.
• To investigate the effect of orthogonal solvent processing and thermal annealing on bilayer morphology.

Main Methods:

• Fabrication of bilayer and BHJ solar cells using poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM).
• Solution processing using orthogonal solvents for bilayers and single solvent for BHJs.
• Analysis of morphology and performance via external quantum efficiency (EQE) measurements and theoretical modeling.

Main Results:

• P3HT/PCBM bilayers from orthogonal solvents exhibit partial intermixing, not sharp interfaces.
• Thermal annealing increases mixing in bilayers but does not yield BHJ morphology.
• Annealed bilayers outperform BHJ devices for thicker active layers.

Conclusions:

• Orthogonal solvent processing for P3HT/PCBM bilayers leads to intermixing rather than distinct layers.
• Morphology control through processing significantly impacts solar cell performance.
• Bilayer structures, when annealed, can offer advantages over BHJs in specific thickness regimes for polymer:fullerene solar cells.