Reduced Nonradiative Voltage Loss in Terpolymer Solar Cells.

Area of Science:

• Materials Science
• Photovoltaics
• Organic Electronics

Background:

• Bulk-heterojunction solar cells rely on efficient exciton dissociation.
• Understanding mechanisms reducing nonradiative photovoltage loss is critical for device efficiency.
• Hybrid local exciton and charge transfer (LE-CT) excitons play a role, but their dissociation is not fully understood.

Purpose of the Study:

• To investigate the energetic and entropic contributions to hybrid LE-CT exciton dissociation.
• To elucidate the mechanism behind reduced nonradiative photovoltage loss in terpolymer-based solar cells.
• To compare terpolymer devices with reference ternary blends.

Main Methods:

• Fabrication and characterization of conjugated terpolymer solar cells.
• Fourier transform photocurrent spectroscopy (FTPS) to identify LE-CT character.
• Temperature-dependent measurements of hole mobility and photovoltage.
• Analysis of energetic disorder.

Main Results:

• Terpolymer devices showed significantly reduced nonradiative photovoltage loss compared to ternary blends, irrespective of the acceptor (fullerene or nonfullerene).
• FTPS confirmed a substantial LE-CT character in terpolymer-based devices.
• Temperature-dependent studies indicated both entropic and energetic contributions to efficient LE-CT dissociation.
• Higher energetic disorder in the terpolymer was identified as the source of the entropic contribution.

Conclusions:

• The study provides fundamental insights into the physics of efficient LE-CT exciton dissociation.
• Terpolymer architecture effectively minimizes nonradiative recombination loss.
• Understanding entropic contributions from polymer disorder is key for designing next-generation efficient organic solar cells.