Visualizing a homogeneous blend in bulk heterojunction polymer solar cells by analytical electron microscopy

Area of Science:

• Materials Science
• Nanotechnology
• Renewable Energy

Background:

• Bulk heterojunctions are crucial for efficient photovoltaic devices.
• Understanding the nanoscale morphology of active layers is essential for optimizing solar cell performance.
• Discriminating between materials with similar characteristics within these layers presents a significant challenge.

Purpose of the Study:

• To develop and apply a method for visualizing and classifying materials in bulk heterojunctions.
• To correlate nanoscale morphology with solar cell efficiency.
• To identify specific morphological features that impact device performance.

Main Methods:

• High-resolution spectroscopic imaging using an analytical transmission electron microscope.
• Nonlinear multivariate statistical analysis for classifying multispectral image data.
• Correlation of nanoscale morphology with measured solar cell efficiency.

Main Results:

• Visual representation of homogeneous donor and acceptor phases, connected by a composite phase.
• Demonstration that the extent of the composite phase depends on fabrication methods.
• First-time correlation of nanoscale morphology variations with solar cell efficiency.
• Visualization of a homogeneously blended phase previously hypothesized to hinder charge separation.

Conclusions:

• The combined technique allows for detailed visualization and classification of bulk heterojunction materials.
• Nanoscale morphology, particularly the presence of a homogeneously blended phase, directly impacts solar cell efficiency.
• This approach provides critical insights for the rational design and fabrication of high-performance photovoltaic devices.