Versatile Sequential Casting Processing for Highly Efficient and Stable Binary Organic Photovoltaics

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Bulk heterojunction (BHJ) morphology is crucial for efficient photon-to-electron conversion in organic solar cells (OSCs).
• The blend casting (BC) method is widely used, but alternative techniques may offer advantages.

Purpose of the Study:

• To investigate the efficacy of sequential casting (SC) for constructing BHJ morphology in OSCs.
• To compare SC with the traditional BC method across different donor:acceptor (D:A) blends.
• To elucidate the morphology evolution and its impact on device performance.

Main Methods:

• Utilized blend casting (BC) and sequential casting (SC) methods.
• Employed three representative D:A blends: PM6:PC71BM, PM6:IT-4F, and PM6:L8-BO.
• Analyzed phase separation, vertical distribution, and D:A ratio-dependent properties.

Main Results:

• Sequential casting (SC) consistently yielded higher power conversion efficiencies (PCEs) compared to BC across all tested blends.
• A champion PCE of 18.86% (certified 18.44%) was achieved with the PM6:L8-BO blend using SC, a record for binary OSCs.
• SC processing led to improved vertical phase segregation, enhancing charge transport and collection, and demonstrated better photostability and scalability.

Conclusions:

• Sequential casting (SC) is a versatile and effective method for fabricating high-performance organic solar cells (OSCs).
• The proposed swelling-intercalation phase-separation model explains morphology development during SC.
• SC offers advantages in device performance, stability, and fabrication scalability for BHJ-based OSCs.