Crystallinity Enhancement and Defect Passivation of All‐Inorganic CsPbI ₂ Br with Phenyltrimethylammonium Tribromide for Stable and Efficient Terahertz Modulation

Compared with organic-inorganic perovskites, cesium-based inorganic perovskites such as CsPbI₂Br have garnered significant interest for terahertz (THz) modulation due to their excellent thermal stability. However, defects present in these inorganic perovskites can serve as charge carrier traps and form recombination centers, which reduce carrier lifetime and modulation depth. To address these issues, phenyltrimethylammonium tribromide (PTABr)-doped CsPbI₂Br films are prepared using a solution spin-coating method. In this doped structure, the PTABr plays a dual function of passivating defects and enhancing structural stability, thereby enabling highly efficient and stable THz modulation. Relative to pristine CsPbI₂Br films, the PTABr-doped films exhibit a uniform, pinhole-free morphology, along with larger grain size, higher crystallinity, and reduced defect density. Moreover, the PTABr incorporation yields a 41% improvement in modulation depth at 0.61 THz. Notably, the doped films retain over 90% of their initial maximum modulation depth after 60 days of storage in an air environment (25 °C, 25% relative humidity (RH)). Thus, this additive engineering strategy offers a promising pathway for developing high-performance and highly stable inorganic perovskite-based THz devices.