Ultrafast spectroscopy on water-processable PCBM: rod-coil block copolymer nanoparticles

Area of Science:

• Materials Science
• Photovoltaics
• Polymer Chemistry

Background:

• Organic solar cells (OSCs) offer a promising alternative to silicon-based photovoltaics due to their flexibility and low-cost processing.
• Water-processable organic solar cells are particularly attractive for large-scale, environmentally friendly manufacturing.
• Block copolymers with distinct donor and acceptor components are key to efficient charge generation in OSCs.

Purpose of the Study:

• To investigate the photophysical properties of water-processable nanoparticles for organic solar cells.
• To understand the impact of hydrophilic coil unit length in rod-coil block copolymers on nanoparticle morphology and photovoltaic performance.
• To provide insights for designing advanced amphiphilic block copolymers for enhanced OSC active layers.

Main Methods:

• Ultrafast spectroscopy was employed to study the photophysics of the nanoparticles.
• Transient absorption spectroscopy was used to analyze exciton dynamics and charge separation processes.
• The study compared nanoparticles with block copolymers containing 2 or 100 hydrophilic coil units.

Main Results:

• Photogenerated excitons in blend nanoparticles migrate to donor/acceptor interfaces for charge separation within tens of picoseconds.
• Increasing hydrophilic coil units from 2 to 100 resulted in long-lived charge transfer states.
• This increase in coil length led to reduced charge generation efficiency in the nanoparticles.

Conclusions:

• Rod-coil block copolymer coil length significantly influences blend nanoparticle morphology and photovoltaic performance.
• Longer coil lengths can impede efficient charge generation by forming long-lived charge transfer states.
• The findings are essential for the rational design of amphiphilic rod-coil block copolymers to improve water-processable organic solar cell efficiency.