Bulk heterojunction is a research area in the field of organic photovoltaics, which focuses on creating efficient and flexible solar cells using a blend of donor and acceptor materials. In bulk heterojunction solar cells, the donor and acceptor materials are mixed at the nanoscale level to create a continuous network of interconnected domains, allowing for efficient charge separation and collection. This approach has shown promise in improving the power conversion efficiency of organic solar cells and has attracted significant research interest in recent years.