Crystal system: monoclinic
| Exciton binding energy, meV |
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Starting materials: lead iodide (PbI2), hydroiodic acid (HI, 57% w/w aqueous, stabilized with H3PO2), ethanolamine (EOA), diethyl ether
Product: Red single crystals (EOA2PbI4)
Description: PbI2 (0.16 g, 0.35 mmol) is dissolved in HI solution (1 mL). Then, EOA (80 μL, 1.3 mmol) is added. This solution is sonicated at room temperature for five minutes. It is then kept at 3 °C in a fridge. Later, red single crystals can be filtered and washed with diethyl ether. They are vacuum dried overnight.
Method: Diffuse reflectance spectroscopy
Description: Powder samples of EOA2PbI4 were used to measure absorption. Linear absorptions can be determined from measurements of UV-vis reflection, and a 2D Elliot formula was used to create a fit for the data. This formula can be found in the supporting information of the referenced publication and the files attached to this dataset. The formula can extract the exciton binding energy of this material. The analysis yields an exciton binding energy of ≈ 46 meV.
Crystal system: unknown
| Exciton binding energy, eV |
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Starting materials: PbO, HI, H3PO2, ethanolamine
Product: spin-coated thin film, high crystallinity and strong exciton absorption
Description: First step: EOA2PbI4 single crystal flakes synthesized as follows: Slow-cooling in HI method: 2.232g (10 mmol) of PbO dissolved in glass vial containing 10 mL of HI and 1.7 mL of H3PO2. Brought to near-boiling temperature. 10 mmol of the organic amine mixed with 5 mL HI, cooled in an ice bath. Solutions were mixed and heated, then cooled to room temperature, upon which single crystal flakes form. Crystals were then washed thrice with diethyl ether and dried under a vacuum. Second step (thin film formation): Flakes were dissolved in 4:1 DMF:DMSO solvent mixture, stirred for 30 minutes. Substrate: quartz substrate with 120 nm gold layer of interdigitated fingers. Precursor solution (0.05-0.1 molar) pipetted onto substrate and then spun at 4000 rpm for 30 seconds, targeting film thickness of 80-300nm. Film was solvent-annealed, then enclosed with 2mL dH2O.
Method: Electroabsorption
Description: Films were spin-coated onto interdigitated Au electrode array - 45 micron distance between opposing fingers. Samples mounted in cryostat with Cu wires soldered to opposing electrode stripes. Xe lamp light spectrally filtered, focused on sample and subsequently on UV-enhanced Si photodiode detector. Sample transmission, substrate transmission, and sample electrotransmission were collected in independent scans.Absorbance and electroabsorbance were then calculated from the respective transmissions. The exciton binding energy arises as the difference of the 1s exciton peak energy observed in conventional absorption and the fundamental gap as determined by the crossover point of absorption curves measured under different electric fields in the fundamental band gap region.
Comment: Significantly more detail in paper.