Mixed-Halide Perovskites with Suppressed Phase Segregation for Large Modulation Depth and High-Stability Terahertz Modulators

Metal-halide perovskites with tunable bandgaps are promising semiconductors in heterojunction engineering for high-performance terahertz modulators. However, most traditional perovskite-based terahertz modulators reported so far are difficult to simultaneously achieve both large modulation depth and high environmental stability in a simple structure. To overcome this bottleneck, herein, the Cs0.25MA0.75PbI2Br/MAPbI3/Si dual-heterojunction terahertz modulator is fabricated using two-step spin-coating method. In this device, the Cs0.25MA0.75PbI2Br film formed by substituting Br- at the X-site and Cs+ at the A-site from MAPbI3 can not only tailor the bandgaps but also suppress the phase segregation, while the MAPbI3 film can promote the accumulation of photon-generated electrons in the Si substrate. Moreover, the maximum modulation depth of the fabricated THz modulator is 71% at 0.42 THz. Compared to the Cs0.25MA0.75PbI2Br/Si or MAPbI3/Si samples, the modulation depth can be increased by almost 100%. After continuous operation in an environment with 70% humidity for 10 h, the device can still operate stably. This study illuminates the potential for high-performance perovskite-based devices, as well as offers new strategies to improve the stability of perovskites.