Solution-Processed ReS ₂ /FAPbI ₃ /p-Si Dual Type-II van der Waals Heterojunctions for Ultrahigh Modulation Depth and Humidity-Resistant Terahertz Modulators

Organic-inorganic hybrid perovskites have emerged as promising candidates for terahertz modulators. However, existing devices suffer from low modulation depth and environmental instability, which severely hinder their practical applications. To overcome these limitations, we fabricated a ReS₂/FAPbI₃/p-Si dual type-II van der Waals heterojunction terahertz modulator using a solution-processed method. In this structure, the FAPbI₃ layer not only acts as a light-absorbing layer but also forms a type-II heterojunction with the underlying p-Si. Simultaneously, the ReS₂ capping layer protects the perovskite from moisture while forming the other type-II heterojunction at the ReS₂/FAPbI₃ interface, thus establishing a dual type-II heterojunction. The resulting THz modulator achieves a modulation depth of over 99% in a broadband range of 0.2-1.0 THz under continuous 800 nm laser illumination at 1500 mW/cm². Moreover, the device retains over 95% of its initial modulation depth even after six months of aging under constant 60% relative humidity or cyclic humidity conditions. Therefore, this work provides a cost-effective and versatile strategy for developing new THz devices with high performance, demonstrating promising potential for applications in THz imaging, communication, and signal processing.