Reversible thermochromism, temperature-dependent conductivity and high stability for a laminated bismuth(iii)-silver(i) hybrid double perovskite

Lead-free hybrid perovskite materials have attracted tremendous consideration due to their applications in photovoltaics, optoelectronics, thermal sensors, etc. Herein, we isolated a new stable semiconductive 2D bismuth(iii)-silver(i) iodide hybrid double perovskite formulated as (H₂MPP)₂[BiAgI₈], where H₂MPP = 1-methylpiperidinium-4-amine, with reversible solid-state thermochromism, a narrow bandgap and considerable temperature-dependent conductivity. Upon heating from 150 K to 450 K, (H₂MPP)₂[BiAgI₈] crystals exhibit a reversible colour change between orange and dark red. The associated structural changes were monitored using in situ single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), UV-visible absorption and Raman spectroscopy. Besides, the electrical conductivity of (H₂MPP)₂[BiAgI₈] changes over four orders of magnitude upon thermochromism (up to 1.51 × 10⁻⁶ S cm⁻¹ at 450 K) and showed an efficiently enhanced photocurrent switching on/off ratio. Moreover, the (H₂MPP)₂[BiAgI₈] crystals can be processed into thin films via spin coating and exhibit high stability under heat and moisture, which is indicative of their potential optoelectronic applications based on thermochromism.