Molecular Design for Vertical Phase Distribution Modulation in High-Performance Organic Solar Cells

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Component distribution in organic solar cells (OSCs) significantly impacts morphology, electronic structure, and performance.
• Optimizing the morphology of the photoactive layer is crucial for efficient charge generation and transport in OSCs.

Purpose of the Study:

• To introduce a molecular design strategy for manipulating component and energetics distribution in OSCs by adjusting side-chain polarity.
• To synthesize and evaluate two non-fullerene acceptors (NFAs) with varying side-chain polarities to understand their impact on film morphology and device performance.

Main Methods:

• Synthesis of two NFAs, ITIC-16F and ITIC-E, by introducing different polar functional substituents onto the side chains of ITIC.
• Fabrication and characterization of OSC devices using these NFAs in a bulk heterojunction blend.
• Analysis of component distribution, vertical energetics, exciton kinetics, and charge transport properties.

Main Results:

• ITIC-16F (hydrophobic) predominantly aligns with the top surface, while ITIC-E (hydrophilic) gravitates toward the bottom of the bulk heterojunction film.
• This differential distribution impacts vertical energy levels, exciton dissociation, and charge carrier transport.
• The OSC device incorporating ITIC-E achieved a power conversion efficiency of 19.4% due to favorable energy distribution.

Conclusions:

• Side-chain polarity manipulation is a viable strategy for designing efficient NFA molecules for OSCs.
• The spatial distribution of energetics within the photoactive layer plays a pivotal role in OSC performance.
• Tailoring molecular structure to control component distribution offers a pathway to enhance OSC efficiency.