High Polymer Molecular Weight Yields Solar Cells with Simultaneously Improved Performance and Thermal Stability

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Organic solar cells (OSCs) require simple synthesis, thick active layers, and stability for large-scale production.
• Donor polymer molecular weight is a critical, yet underexplored, parameter for optimizing OSC performance.

Purpose of the Study:

• Investigate the impact of donor polymer molecular weight on organic solar cell performance and stability.
• Explore the relationship between molecular weight, morphology, charge transport, and device efficiency.
• Assess the thermal stability of organic solar cells with varying donor polymer molecular weights.

Main Methods:

• Synthesized PTQ10 donor polymer with a range of number average molecular weights (2.4–54.4 kDa).
• Fabricated organic solar cells using PTQ10 and three non-fullerene acceptors (Y6, Y12, IDIC).
• Analyzed device performance, spectroscopic properties, grazing-incidence wide-angle X-ray scattering (GIWAXS), and charge carrier mobility.

Main Results:

• A threefold increase in power conversion efficiency was observed with increasing molecular weight.
• Achieved over 10% power conversion efficiency in blade-coated devices with active layer thicknesses of 200–350 nm using high molecular weight PTQ10.
• Photocurrent improvement correlated with enhanced electronic transport and increased polymer contribution to exciton generation.
• Higher molecular weight PTQ10 resulted in improved thermal stability due to a higher glass transition temperature.

Conclusions:

• Donor polymer molecular weight is a key parameter for enhancing organic solar cell efficiency and stability.
• High molecular weight PTQ10 enables efficient and stable thick-film organic solar cells.
• Optimizing molecular weight offers a promising strategy for upscaling organic photovoltaics.