Organic solar cells (OSCs) have a bright prospect across applications where light weight, flexibility, low costs, and semi-transparent properties are essential. [1-4] Over the years, tremendous efforts have been devoted to the material design, device engineering, theoretical exploration, and large area manufacture of OSCs. [5-9] With Y6 [10] and its derivatives as acceptors, power conversion efficiencies (PCEs) of over 16% have now

Quaternary organic solar cells (q-OSCs) achieve a power conversion efficiency (PCE) of 17.73%, which is by far the highest reported PCE to date for q-OSCs. The quaternary devices significantly outperform the corresponding binary and ternary devices with various material combinations displaying the enormous potential of the quaternary blend system through rational design. We demonstrated a new type of ''rivers and streams'' hierarchical morphology that allows for the achievement of highly efficient quaternary devices that were considered extremely challenging in the past.

Small molecular acceptors (SMAs) have gained extensive research attention as they offer many attractive features and enable highly efficient organic solar cells (OSCs) that cannot be achieved using fullerene acceptors....

Significant development has been achieved in nonfullerene organic solar cells. However, most of the high‐efficiency nonfullerene systems are composed of polymer donors and fused‐ring acceptors, and only a few small molecule donors can work well. Herein, a new A–D–A small molecule donor named NDTSR with naphtho[1,2‐b:5,6‐b′]dithiophene (NDT) as building blocks is synthesized. Two energy levels well‐matched fused‐ring acceptors ITIC and IDIC are chosen to construct all‐small‐molecule solar cells with NDTSR, respectively. When mixed with IDIC, a high power conversion efficiency (PCE) of 8.05% is achieved, which is the highest efficiency for NDT‐based small molecule donor. However, the NDTSR:ITIC system only exhibits a low PCE of 1.77%. The big difference in the performance of these two systems should be attributed to the different morphology and phase separation resulting from the crystallinity and aggregation ability of the acceptors. The results demonstrate that NDT‐based small molecule is a promising candidate donor for all‐small‐molecule systems, while the crystallinity of fused‐ring acceptors is a critical factor for optimizing the phase separation in the active layer.