Fig. 1. (a) Crystal structure diagram of PEA₂PbI₄. (b) X-ray diffraction spectrum of (PEA)₂PbI₄. (c) Optical microscope image (top) and fluorescence image (down) of a representative exfoliated sample. (Green dotted area: (PEA)₂PbI₄; yellow dotted area: BN.) (d) Spectral comparison at 78 K and room temperature.

Fig. 2. (a) Intensity of the four emission peaks varies with the excitation power, and linear fitting is adopted. (b) Experimental setup for polarization-resolved measurements. (c) Polarized PL spectra taken at 78 K at selected detection angles of β = 0° and 90° by fixing the excitation polarization to α = 0°. Inset: the relationship between the PL intensity of the P1 peak and the detection angle β fitted with the sine function. (d) Schematic diagram of the device with the loading of an electric field (E).

Fig. 3. (a),(d) Voltage-dependent PL spectra. (b),(e) The changes in the PL intensity of the four peaks, and the changes in the ratios of P1, P2, and P3 at 78 K at selected detection angles of (a)–(c) β = 90° and (d)–(f) β = 0° at a fixed angle of excitation light (α = 0°).

Fig. 4. (a) Schematic illustration of the detector. (b) Photocurrents under different voltages at different excitation polarizations. Photocurrents at different excitation polarizations at (c) 30 V and (d) −30 V.