Mixed ligands exchange method
Mixed ligands solution was prepared by dissolving 1 mg of X-type ligand and 1 mg of L-type ligand in 1 mL of ethyl acetate.
CsPbI3 perovskite quantum dots (PQDs) solution was deposited on the substrate using spin coating method.
The CsPbI3 PQD solids were soaked with mixed ligands solution during 10 s for solid-state ligand exchange.
Fabrication of perovskite quantum dot light emitting diodes
The PEDOT:PSS solution was deposited on ITO substrate at 4500 rpm for 40 s and annealed at 140 °C for 10 min. Sequentially, poly-TPD layer was deposited on the PEDOT:PSS layer at 4000 rpm for 40 s and annealed at 120 °C for 5 min.
The CsPbI3 PQD solution (30 mg/mL) was deposited on the hole-transporting layer followed by solid-state ligand exchange using mixed ligand solution.
Finally, TPBi (75 nm), LiF (1 nm), and Al (100 nm) were deposited by using a thermal evaporator.
Full device structure : ITO/PEDOT:PSS/poly-TPD/PQDs/TPBi/LiF/Al.
Figure. 1 (a) Schematic illustration of mixed ligand exchange method. (b) PLQY spectra and photograph images of PQD solids. (c) Schematic illustration of full device structure. (d) Luminance and (d) EQE curves of each LED device.
Table 1. Performance of each LED device.
Characterization
The photoluminescence quantum yields (PLQYs) of the film of PQD solids were carried out by using HAMAMATSU, Quantaurus-QY. Luminance and EQE curves of LED devices were measured by using Konica
Minolta spectroradiometer (CS-2000) with a Keithley 2400 sourcemeter.