Asymmetrified Benzothiadiazole-Based Solid Additives Enable All-Polymer Solar Cells with Efficiency Over 19 

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Disordered polymer chain entanglements hinder optimal donor-acceptor phase separation in all-polymer blends.
• Effective methods for regulating morphology evolution are crucial for advancing all-polymer organic solar cells (APSCs).

Purpose of the Study:

• To design and investigate the effect of two isomeric solid additives, SF-1 and SF-2, on the morphology and performance of all-polymer organic solar cells.
• To explore how these additives influence molecular packing, phase separation, and exciton dynamics in polymer blends.

Main Methods:

• Synthesis of two isomeric solid additives (SF-1 and SF-2) based on the benzothiadiazole unit.
• Incorporation of SF-1 or SF-2 into PM6:PY-DT polymer blends.
• Characterization of film morphology, molecular packing, and exciton diffusion lengths.
• Fabrication and performance testing of organic solar cell devices.

Main Results:

• SF-1 and SF-2 incorporation induced stronger molecular packing and continuous interpenetrated networks with optimized phase separation and vertical distribution.
• Exciton diffusion lengths in PY-DT films were extended to over 40 nm, enhancing exciton diffusion and charge transport.
• The asymmetrical SF-2 additive, with its enhanced dipole moment, increased the power conversion efficiency (PCE) of PM6:PY-DT devices to 18.83% due to stronger electrostatic interactions.
• A ternary device strategy further boosted the PCE of SF-2-treated APSCs to over 19%.

Conclusions:

• Rational design of solid additives can effectively manipulate the morphology of all-polymer blends.
• SF-1 and SF-2 are promising additives for enhancing the performance of all-polymer organic solar cells.
• This study presents a highly effective approach for achieving high-performance APSCs, demonstrating PCEs exceeding 19%.