Broadband All‐Inorganic Perovskite Photodetector Based on Type‐II CsPbI 3 Nanocrystals/CsPbBr 3 Single‐Crystal Heterojunction

All‐inorganic CsPbBr 3 single‐crystals (SCs) are premier candidates for high‐performance photodetection due to low defect densities, long carrier diffusion lengths, and intrinsic thermal stability. Because the intrinsic bandgap of CsPbBr 3 corresponds to the blue‐green spectral range, CsPbBr 3 SC photodetectors exhibit limited direct photoresponse to red and near‐infrared light. Here, we report a broadband photodetector based on a novel Type‐II heterojunction formed by CsPbI 3 nanocrystals (NCs) and CsPbBr 3 SC. To circumvent the charge‐transport bottlenecks of NCs caused by insulating long‐chain ligands, we implement ligand‐exchange using short‐chain conjugated ligand 1‐naphthylamine (NA). NA effectively passivates surface defects and improves charge transport efficiency of CsPbI 3 NCs by 8.7 times. In the proposed Type‐II heterojunction, the CsPbBr 3 SC likely acts as both a synergistic active layer and a hole‐transport medium, enabling efficient vertical carrier extraction across the NC/SC interface. The resulting photodetector achieved a broad response range from 350 to 800 nm. Performance metrics include a responsivity of 2.62 A/W, a specific detectivity of 2.34 × 10 13 Jones, and a wide linear dynamic range of 161 dB at 650 nm. The photodetector also demonstrates exceptional thermal robustness, maintaining stable operation at 190°C, which is one of the highest operating temperatures reported for perovskite‐based photodetectors.