1. (a) Structure of the photodetector device prepared on a glass substrate, (b) schematic diagram of preparation process for the (PEA)₂PbI₄ thin film, and (c) SEM image of the (PEA)₂PbI₄ thin film after being annealed at 80 ℃

2. (a) XRD pattern of a typical (PEA)₂PbI₄ film,(b) crystal structure of two-dimensional layered (PEA)₂PbI₄, and (c) UV-Vis absorption and (d) PL spectra of (PEA)₂PbI₄ film

3. (a) Dark current versus applied voltage, (b) dark current versus time in the dark state, (c) I-V curves, and (d) I-t curves illuminated at different wavelengths with 1 mW/cm² for (PEA)₂PbI₄ photodetector

4. (a) I-V and (b) I-t curves illuminated at 450 nm with different light intensities, (c) fitted line of photocurrent vs. light intensity illuminated at 450 nm, (d) responsivities and detectivities at different light intensities, (e) response time and (f) noise currents tested at different frequencies for (PEA)₂PbI₄ photodetector

5. Stability of the 2D (PEA)₂PbI₄ film and photodetector

S1. (a) Picture of a photodetector based on (PEA)₂PbI₄ film; (b) SEM image of (PEA)₂PbI₄ film after being annealed at high temperature(200 ℃)

S2. EDS mappings of (PEA)₂PbI₄ thin film

S3. XRD patterns of (PEA)₂PbI₄ without and with DMF treatment before spin-coating

S4. Tauc plot of (PEA)₂PbI₄ film with an optical band gap of 2.357 eV

S5. Bias-dependent photoconductivity of (PEA)₂PbI₄

S6. I-V curves of photodetector with up-electrode in the light-dark state