Crystal system: triclinic
| Exciton binding energy, eV |
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Starting materials: 200 mg (0.90 mmol) of PbO and 200 μL (1.59 mmol) of phenylethylammonium, fully dissolved in 4 mL of HI and 0.5 mL of H3PO2 solution.
Product: Exfoliated single crystal flakes of (PEA)2PbI4.
Description: 2D perovskite PEPI single crystals are synthesized based on previously reported slow-cooling method in Ref. https://dx.doi.org/10.1021/acsenergylett.8b01315. 200 mg (0.90 mmol) of PbO and 200 μL (1.59 mmol) of phenylethyl- ammonium are fully dissolved in 4 mL of HI and 0.5 mL of H3PO2 solution at 90 °C. The solution is then slowly cooled to room temperature at a rate of 2 °C h−1, giving orange sheet-like crystals. The crystals are then isolated from the parent solution by vacuum filtration, washed by a small amount of diethyl ether, and dried under vacuum. Thin crystals were exfoliated from the parent crystal using stiff heat release tape that serves as a handle. Sequential exfoliation steps with the tape yield successively thinner crystals. Many crystals were surveyed to select the best surface quality, flatness, and area.
Comment: Note that, while an XRD pattern was reported in this work, the XRD analysis and the space group were not reported and the space group listed here was taken from DOI: 10.1021/acs.inorgchem.7b01094.
Method: Reflection mode and transmission mode ellipsometry
Description: Transmittance was collected on a Cary 7000 UV-VIS-NIR spectrophotometer. Reflection ellipsometry was collected on a JA Woollam M2000DI at 45° to 75° using tape to suppress backside reflections. Transmission ellipsometry was collected on a JA Woollam M2000DI from −10° to 70°. The three data sets were processed as a multisample analysis in CompleteEASE. For bulk and cleaved crystals, reflection ellipsometry and reflection Mueller Matrix were collected using focus probes and either a JA Woollam M2000 or RC2, respectively.
Comment: Exciton energies were extracted from a uniaxial model of the ellipsometry data (2.385(5) eV in-plane and 2.419(7) eV out-of-plane). The exciton binding energy of 0.259 eV was calculated using ellipsometry dielectric parameters, an electron-hole image charge model and the experimental effective mass of DOI: 10.1021/acs.jpclett.0c03731.