Simultaneously Achieving Highly Efficient and Stable Polymer:Non-Fullerene Solar Cells Enabled By Molecular Structure...

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Developing stable non-fullerene acceptors (NFAs) is crucial for advancing polymer solar cells (PSCs).
• Existing research on NFA molecular structure's impact on PSC stability and efficiency is limited.
• Long-term stable PSCs often exhibit lower efficiencies.

Purpose of the Study:

• To investigate the relationship between NFA molecular structure and the stability of inverted PM6:NFA solar cells.
• To identify molecular design strategies for enhancing NFA stability in PSCs.
• To achieve high efficiency and long operational lifetime in PSCs.

Main Methods:

• Comparative stability analysis of PSCs with different NFAs (ITIC, IT-4F, Y6, N3).
• Quantum chemical calculations to understand degradation mechanisms.
• Device fabrication incorporating ZnO surface passivation with phenylethanethiol (PET).
• Performance and stability testing of modified NFA-based PSCs.

Main Results:

• A decay rate order of IT-4F > Y6 ≈ N3 > ITIC was determined for the tested NFAs.
• Fluorine substitution was found to weaken C═C bonds and increase NFA-ZnO interaction.
• Bulky β-alkyl side chains on thiophene units were shown to inhibit radical attack on C═C bonds.
• A novel NFA (L8-BO) with bulky side chains exhibited reduced photodegradation and performance decay.
• PSCs with L8-BO, ZnO passivation, and PET achieved 17% efficiency and projected T80/Ts80 of 5140/6170 hours.

Conclusions:

• Functionalizing the β-position of the thiophene unit in NFAs is an effective strategy for improving PSC device stability.
• Molecular design of NFAs plays a critical role in achieving both high efficiency and long-term operational stability in PSCs.
• Surface passivation techniques further enhance the stability and performance of NFA-based PSCs.