Phase-pure ferroelectric quantum wells with tunable photoluminescence for multi-state optoelectronic applications

Abstract

Quasi-two-dimensional (quasi-2D) metal halide perovskite (MHP) ferroelectrics, characterized by spontaneous polarization and semiconducting properties, hold promise for functional photoferroelectrics in applications such as optical storage and in-memory computing. However, typical quasi-2D perovskite films contain multiple quantum wells with random width distribution, which degrade optoelectronic properties and spontaneous polarization. Here, we introduce phase-pure quantum wells with uniform well width by incorporating the inorganic salt MnBr₂, which effectively controls crystallization kinetics and restricts the nucleation of high n-phases, producing high-quality films. The resulting (BA)₂CsPb₂Br₇ (BA = C₄H₉NH₃) film demonstrates ferroelectric hysteresis behavior, clear in-plane ferroelectric domain switching, and a high photoluminescence quantum efficiency (PLQE) of 88.7%. Significantly, we observed a nonvolatile, reversible in situ photoluminescence (PL) modulation of Mn²⁺ in this ferroelectric MHP film under an applied electric field, attributed to lattice distortion from ferroelectric polarization orientation. These findings enabled the development of a simple system comprising gallium nitride (GaN) light emitting diodes (LEDs) and ferroelectric films to implement multi-state signal encoding and a logic AND gate. This work advances the fabrication of efficient ferroelectric MHP films and highlights their potential for advanced optoelectronic applications.

Fig. 1. Schematic diagram for nucleation and growth processes.

a, b The nucleation and growth processes of (BA)₂CsPb₂Br₇ MHP films without and with MnBr₂ added. a The cyan dotted circle represents colloidal precursor sol-gel Cs⁺/PbBr_x⁻ complexes, which formed spontaneously in the precursor solution. The colloids provided nucleation sites for the subsequent crystallization. b The incorporation of MnBr₂ changed the solvent acidic, dissolving the colloids in the perovskite precursor solution. The cations are evenly distributed in the precursor solutions

Fig. 2. Structural and optical characterizations.

a, b SEM images of pristine film and 6% MnBr₂ added film, respectively. c XRD patterns of the 0–8% MnBr₂ added films. d XPS spectra of pristine and 6% MnBr₂ added films for the binding energy regions corresponding to the Cs 3d, Pb 4f, Br 3d. e, f UV-vis absorption spectra, PL spectra of the 0–8% MnBr₂ added films (inset is the local magnification of the PL spectra). g, h PDOS of pristine film and 6% MnBr₂ added film, respectively

Fig. 3. The phase distribution regulated by MnBr₂.

a, b TAS under different delay times for pristine and 6% MnBr₂ added films, respectively. c, d TA dynamic curves and fitting results of n = 2 and n = 3 phases in pristine and 6% MnBr₂ added films, respectively. e, f Time varying in situ PL spectra of pristine and 6% MnBr₂ added films. g, h The variation of PL intensity of different n-phase over time, which are the integral results of (e, f)

Fig. 4. Ferroelectricity regulates the luminescence.

a Lateral PFM phase image of the after applying a tip voltage V = ± 10 V to the 6% MnBr₂ added film. b Contour plot of voltage-dependent PL spectra. c The PL intensity and PL decay time of Mn²⁺ as a function of applied voltage, respectively. d W-H plots of 6% MnBr₂ added film under 0, ±6 V voltage. e Schematic illustration of the energy transfer mechanism. f Time-dependent PL intensity after the applied pulse voltage was withdrawn. g PL intensity and lattice distortion (ɛ) as a function of applied voltage, respectively

Fig. 5. Voltage-dependent PL intensity.

a–f PL intensity modulation of the 6% MnBr₂ added film by imposing pulse voltage with different pulse widths. The lower curve represents the applied pulse voltage, while the upper curve shows the variation of PL intensity with the applied voltage. g Diagram of electric field modulation of PL intensity, where fig. g2 is the initial ferroelectric polarization state, fig. g1 and fig. g3 show the ferroelectric polarization states with completely and incompletely switched, respectively

Fig. 6. Multi-state signal encoding and logic AND gate functions in proof-of-concept devices.

a–c Optoelectronic communication demonstration of PL intensity modulation devices. From top to bottom, the switch of the GaN LED and the applied voltage are used as input signals, and the monitored PL intensity is used as the output signal. d–f Working principle and demonstrations of logic AND gate. Schematic and operating principle of logic AND gate (d). 3D bar plot of the normalized PL intensity of 6% MnBr₂ added film (e). The normalized PL intensity above and below 0.5 threshold is considered as output codes “1” and “0”, respectively. The dynamic demonstration of logic AND gate (f)