Giant Near-Room-Temperature Pyroelectric Figures-of-Merit Originating from Unusual Dielectric Bistability of Two-Dimensional Perovskite Ferroelectric Crystals

Pyroelectric materials with the capability of converting temperature changes into electrical signals have been widely used as essential elements for assembling integrated smart electronic detectors. Regarding the conversion efficiency of the voltage output, however, it is significant but quite challenging to exploit new candidates with large pyroelectricity figures-of-merit (FOMs) at room temperature. Herein, we have acquired giant near-room-temperature pyroelectric FOMs in the two-dimensional (2D) perovskite-type improper ferroelectric crystals of (BA)2(EA)2Pb3I10 (1, where BA = n-butylammonium and EA = ethylammonium), for which the room-temperature voltage FOM (Fv = 1.06 × 10–2 cm2/μC) is about 10 times as large as that of the state-of-the-art inorganic oxides (often ∼0.1 × 10–2 cm2/μC), while the peak values near the Tc are almost 2–3 orders of magnitude higher than those of the typical oxide counterparts. Such ultrahigh FOMs are mainly due to their large pyroelectric coefficients and unusual bistability of dielectric behavior, that is, an extremely small-amplitude dielectric variation caused by dipole reorientations during the ferroelectric-to-antiferroelectric phase transition at ∼315 K. This achievement of ultrahigh pyroelectric FOMs in improper ferroelectrics is in sharp contrast to the proper counterparts. Moreover, the low-cost and facile integration of crystal-based devices favors their great potential as smart pyroelectric detectors. As far as we know, the findings of giant pyroelectricity FOMs are unprecedented in 2D hybrid perovskites, which probably recall their broader prospects toward high-performance electronic device application.