Photoelectric properties surge driven by molecular-ionic crystal transition in layered antimony triiodide under high pressure

Establishing an effective interconnection between the crystal structure and photoelectric-related properties in layered materials is paramount for fostering efficient energy conversion. Here, we present a systematic demonstration of the adjustable and fascinating photoelectric properties alongside the intriguing molecular-ionic crystal transition in layered SbI ₃ under high pressure. With increasing pressure, the photocurrent response of SbI ₃ exhibits a dramatic enhancement, reaching a maximum of 100 mA/W at 4.4 GPa, which is nearly ten times the value (8 mA/W) at initial pressure, while maintaining an ultra-low dark current simultaneously. The substantial enhancement in photoelectric responses of SbI ₃ is intimately associated with the molecular to ionic isostructural phase transition, which is accompanied by an increase in coordination number and charge delocalization. Conversely, the crystal structure transition from hexagonal to monoclinic with a reduction in coordination number could cause a dramatic attenuation in photoelectric activities under higher pressure. These findings signify that the strong ionic crystal character, high coordination number and high charge delocalization would enormously contribute to photoelectric properties surge in layered metal halides, and this could potentially be extended to other layered functional materials to tune photoelectric-related properties.