Research On High-quality Perovskite Films And Light-Emitting Devices Based On Surface Passivation

In recent years,the perovskite light-emitting diode(PeLED)has shown great application potential due to its defect tolerance characteristics,high color purity,and solution processing.Its efficiency has rapidly increased from the initial 0.1%to 21.6%in just a few years.Generally,the perovskite luminescent layer is prepared by solution spin coating method.Although this method is simple and low in cost,the prepared film tends to have poor morphological quality and high density of defect states,which not only affects the stability of the PeLED device.It also limits the further improvement of its efficiency.Based on the preparation of uniform,dense and low defect state density perovskite luminescent layer,the surface post-treatment process is used to improve the quality of the perovskite film morphology and reduce the defect state density.Two kinds of surface passivating agents were selected,namely,a CsBr passivation layer was deposited on the surface of quasi-2D blue perovskite BA2Csn-1(Cl/Br)3n+1,and a BABr passivation layer was spin-coated on the surface of 3D perovskite CsPbBr3.Both perovskite films and PeLED devices with good performance were prepared.The specific research progress is as follows:(1)Select the all-inorganic perovskite CsPbClxBr3-x with good thermal stability and adjust the Cl content to shift the wavelength of the emitted light from the green range to the blue range.The final composition of the perovskite is CsPbCl1.0Br2.0 to the solubility limitation.Then BABr was added to the CsPbCl1.0Br2.0 precursor solution to prepare quasi-2D perovskite,then the CsBr was deposited on the surface of the prepared quasi-2D perovskite film.The crystal structure,surface morphology and spectral characteristics of the perovskite luminescent layer shows that CsBr deposited on the surface of the perovskite will not affect its crystal structure,but CsBr can fill the pinholes of the quasi-2D perovskite,passivate the defects at the grain boundaries,thus effectively increased the proportion of radiation recombination.Compared with the initial perovskite,the performance of the blue PeLED device was the best after vapor deposition of 1 nm CsBr on the surface,and the EQE increased from 0.91%to 1.73%.(2)A simple two-step solution spin coating method was used to prepare CsPbBr3 perovskite,followed by spin coating of the isopropyl alcohol solution of BABr.The BABr-CsPbBr3 perovskite luminescent layer was prepared by precisely controlling the infiltration time and concentration of the BABr solution on the thin surface of the perovskite.The CsPbBr3 perovskite thin films post-treated with different concentrations of BABr were characterized for structural morphology and performance of luminescence.The BABr post-treatment process will induce perovskite recrystallization,which will reduce the number of pinholes on the film surface and increase the coverage.In addition,the combination of BABr and perovskite can passivate the defects on the film surface and the perovskite grain boundaries,reduce the defect state density of the film,and thus effectively inhibit non-radiative recombination.Compared with the original device,the performance of the device after 7 mg/mL BABr passivation is the best,it’s EQE reaches 3.90%,and has good repeatability.At the same time,due to the reduced density of defect states and the hydrophobic effect of long-chain organic groups in BABr,the stability of the device has been significantly improved,and the half-life in the air environment reaches 68 s.