Morphology-dependent trap formation in bulk heterojunction photodiodes

Area of Science:

• Materials Science
• Photovoltaics
• Polymer Chemistry

Background:

• Nanostructured polymer solar cells offer a promising renewable energy avenue.
• Understanding degradation mechanisms is crucial for improving device longevity.
• Local structural variations can significantly influence material properties and performance.

Purpose of the Study:

• To investigate the effect of local structural variation on the aging rate of nanostructured polymer solar cells.
• To compare time-resolved electrostatic force microscopy (trEFM) and conventional device measurements.
• To elucidate the degradation pathways in polymer blends under photooxidation.

Main Methods:

• Fabrication and characterization of photovoltaic devices using 1:1 blends of PFB and F8BT.
• In situ photooxidation of polymer films using 365, 405, and 455 nm illumination.
• Time-resolved electrostatic force microscopy (trEFM) and conventional device measurements to monitor changes.

Main Results:

• Faster loss of photocurrent generation observed in F8BT-rich domains during photooxidation.
• PFB-rich phases exhibited higher photoresponse even at wavelengths predominantly absorbed by F8BT.
• Evidence of more rapid degradation of PFB hole-transport pathways in F8BT-rich regions.

Conclusions:

• Local structural variations significantly affect the aging rate of polymer solar cells.
• Degradation kinetics are domain-dependent, influencing overall device performance.
• Loss of percolation pathways for hole transport in F8BT-rich phases contributes to device aging.