Coupled pyroelectric-photovoltaic effect in 2D ferroelectric $α$-In$_2$Se$_3$

Abstract: Pyroelectric and photovoltaic effects are vital in cutting-edge thermal imaging, infrared sensors, thermal and solar energy harvesting. Recent advances revealed the great potential of the bulk photovoltaic effect in two-dimensional (2D) semiconductor-ferroelectric materials to enable reconfigurable p-n junction operation with the potential to surpass the Shockley-Queiseer limit. Moreover, the extremely low thickness, high thermal conductivity, dangling bonds free interface, and room-temperature stable ferroelectricity down to a single monolayer endow 2D ferroelectrics with a superior pyroelectric figure of merit. Herein, we performed direct pyroelectric measurements of 2D $\alpha$-In$_2$Se$_3$ under dark and light conditions. The results reveal a gigantic pyroelectric coefficient of 30.7 mC/m$^2$K and a figure of merit of 135.9 m$^2$/C. In addition, we perform temperature-dependent short-circuit photovoltaic response measurements in which the excess photocurrent is modulated in proportion with the temperature variations due to the induced in-plane potential variations. Consequently, the discovered pyroelectric-photovoltaic effect allows the combination of direct temperature (photovoltaic) and temperature-derivative (pyroelectric) sensing. Finally, we utilized the intercoupled ferroelectricity of In$_2$Se$_3$ to realize a non-volatile, self-powered photovoltaic memory operation, demonstrating a stable short-circuit current switching with a decent 103 ON-OFF ratio. The coupled pyroelectric-photovoltaic effect, along with reconfigurable photocurrent, pave the way for a novel monolithic device technology with integrated thermal and optical response, in-memory logic and energy harvesting.