The Institute

Title: Two-Dimensional Dion−Jacobson Ferroelectric Semiconductors with an Out-of-Plane Polarization and Ultraviolet Photoluminescence

Authors: M. Mączka*, D. Drozdowski, K. Fedoruk-Piskorska, J. Kudrawiec, B. Popanda, J. K. Zaręba, R. Bartoszewicz, A. Sieradzki

Journal: Chemistry of Materials

DOI: 10.1021/acs.chemmater.6c01732

The miniaturization of ferroelectric and solar-cell devices requires out-of-plane polarization in 2D materials. Unfortunately, only four lead halide ferroelectrics with out-of-plane polarization have been reported to date. In this article, Prof. Mączka with co-workers and collaborators report the discovery of two new hybrid lead chloride perovskites with out-of-plane polarization: the single-layered (MPDA)PbCl₄ and the bilayered (MPDA)(MA)Pb₂Cl₇ (MPDA = N-methyl-1,3-propanediamine). Both compounds exhibit efficient second-harmonic generation (SHG) at room temperature together with a broad optical transparency window extending into the ultraviolet region. Structural studies revealed that both materials undergo a phase transition from a high-temperature phase (C2/c and C222 for (MPDA)PbCl₄ and (MPDA)(MA)Pb₂Cl₇, respectively) to a room-temperature ferroelectric Pn phase with out-of-plane spontaneous polarization. The ferroelectric nature of (MPDA)PbCl₄ was further confirmed by the observation of ferroelectric hysteresis loops. Optical measurements showed that (MPDA)PbCl₄ and (MPDA)(MA)Pb₂Cl₇ display distinct photoluminescence with narrow and broad emission bands centered at approximately 354 and 410 nm, respectively.

In summary, Prof. Mączka’s work demonstrates that the incorporation of the MPDA²⁺ cation and a mixed-cation design strategy provide an effective route toward hybrid lead chloride perovskites combining out-of-plane ferroelectricity, nonlinear optical activity, and tunable photoluminescence, making them promising candidates for advanced photonic and optoelectronic applications.

• Synthesis of two new hybrid lead chloride perovskites, (MPDA)PbCl₄ and (MPDA)(MA)Pb₂Cl₇, exhibiting out-of-plane spontaneous polarization and efficient room-temperature second-harmonic generation (SHG).
• Identification of structural phase transitions leading to ferroelectric room-temperature phases with polar Pn symmetry.
• Experimental confirmation of ferroelectricity in (MPDA)PbCl₄ through the observation of ferroelectric hysteresis loops.
• Demonstration of broad optical transparency extending into the ultraviolet region, combined with distinct narrow and broad photoluminescence emissions centered at approximately 354 and 410 nm.