Giant Pyroelectric Figure of Merits in Strain-Engineered Ferroelectric 2D-SnSe Layered Nanosheets: An Efficient Transient Thermal Energy Harvester

Two-dimensional (2D) layered semiconductors reveal boundless potential in next-generation ferro-, piezo-, and pyroelectric property-based self-powered devices. In this scenario, we report the experimental observations, which are consistent with the first-principles calculations of the out-of-plane ferro- and piezoelectricity in 2D tin selenide (SnSe) of van der Waals-bonded monolayers. It has a strain-engineered, synergetic trigonal crystal structure. Thin 2D-SnSe nanosheets of a few monolayers are exfoliated from bulk orthorhombic SnSe, which facilitates enormous potential of out-of-plane pyroelectric-aided transient thermal energy harvesting. In particular, phase and amplitude hysteresis of piezoresponse force microscopy affirms that the van der Waals-bonded trilayer SnSe nanosheets exhibit profound ferro- and piezoelectric (d₃₃ ∼ 3.45 pm/V) responses. A robust pyroelectric response persists with a figure of merit (F_v ∼ 8 m² C^–1 and F_D ∼ 132 × 10^–6 Pa^–1/2), an order higher than the commercially benchmark bulk pyroelectrics. Hence, 2D-SnSe layers could be promising materials for pyroelectric-based waste heat scavenging, infrared imaging, and detectors for various applications.