Enhanced Fibrillar Network and Molecular Crystallization via Volatile Solid Additives Enable Efficient Near‐Infrared Organic Photodetectors

Abstract Controlling the phase separation and domain purity of organic semiconductors to form well‐developed nanoscale morphology optimization in the bulk‐heterojunction active layer is critical yet challenging for building high‐performance organic photodetectors. Herein, an effective morphology controlling method by applying a small molecule IC‐Br as the solid additive is demonstrated, which can effectively restrict the overmix of the PTzBI‐Si:IEICO‐4F in the process of film formation. The film processed with IC‐Br formed well‐developed nanoscale phase separation with bi‐continuous interpenetrating networks, which exhibited enhanced π–π stacking and the improved domain purity of the IEICO‐4F phase, resulting in a significant decrease in the density of the trap state compared to the pristine film. Consequently, the device processed with IC‐Br additive enabled a high specific detectivity of 3.8 × 10¹³ Jones at 860 nm under −0.1 V associated with the improved linear dynamic range and response speed, indicating the strong visible‐to‐near infrared detecting capability and potential for practical applications. The morphology optimization strategy established in this work may offer unprecedented opportunities to build state‐of‐the‐art OPDs.