Structural Transition‐Mediated Tuning of Liquid Crystal Excitonic Coupling for Enhanced Photodetection in Organic–Inorganic Heterostructures

ABSTRACT Van der Waals heterostructures (HSs) composed of 2D materials and organic semiconductors (OSCs) exhibit a range of compelling optoelectronic properties. However, the correlation between the morphology of solution‐processed OSCs on top of 2D materials and the corresponding optoelectronic device performance of such HSs remains largely unexplored. Herein, we fabricated a heterojunction photodetector (PD) by simply spin‐coating a liquid crystalline swallow tail containing perylene bisimide (PBI ^ST ) solution on top of an amorphous In ₂ Se ₃ ( a ‐In ₂ Se ₃ ). We demonstrate the impact of liquid crystalline PBI ^ST morphology on the photodetection performance of PBI ^ST / a ‐In ₂ Se ₃ HS. The as‐deposited HS exhibits 3D random in‐plane arrangement of PBI ^ST , whereas annealing at 80°C induces a uniform, short‐range, 2D‐like morphology of PBI ^ST molecules. This structural transition enhances the responsivity (R) and external quantum efficiency (EQE) by 166% for annealed HS w.r.t . pristine HS. The enhanced performance for annealed HS stems from the 2D‐like morphology of PBI ^ST , which ensures better in‐plane coverage and uniform interface with a ‐In ₂ Se ₃ , increases exciton bandwidth, and minimizes energetic disorder, collectively boosting charge transfer and Förster resonance energy transfer. The annealed HS exhibits impressive performance metrics: R ∼ 0.8 A/W, detectivity (D) ∼4.5 × 10 ¹¹ Jones, and EQE ∼ 247%, which are impressive in the context of organic–inorganic HS‐based PDs.