Solid Additive Engineering for Next-generation Organic Photovoltaics.

Solution-processed bulk heterojunction (BHJ) organic solar cells (OSCs) have emerged as a promising next-generation photovoltaic technology. In this emerging field, there is a growing trend of employing solid additives (SAs) to fine-tune the BHJ morphology and unlock the full potential of OSCs. SA engineering offers several significant benefits for commercialization, including the ability to i) control film-forming kinetics to expedite high-throughput fabrication, ii) leverage weak noncovalent interactions between SA and BHJ materials to enhance the efficiency and stability of OSCs, and iii) simplify procedures to facilitate cost-effective production and scaling-up. These features make SA engineering a key catalyst for accelerating the development of OSCs. Recent breakthroughs have shown that SA engineering can achieve an efficiency of 19.67% in single-junction OSCs, demonstrating its effectiveness in promoting the commercialization of organic photovoltaic devices. This review provides a comprehensive overview of significant breakthroughs and pivotal contributions of emerging SAs, focusing on their roles in governing film-forming dynamics, stabilizing phase separation, and addressing other crucial aspects. The rationale and design rules for SAs in highly efficient and stable OSCs are also discussed. Finally, the remaining challenges are summarized, and perspectives on future advances in SA engineering are offered.