Fabrication of LED devices-
ITO-coated glass substrates were cleaned in an ultrasonic bath with deionized water, acetone, and IPA for 15 min and dried in the oven at 80 ◦C overnight.
They were then treated with plasma for 15 minutes after which they were transferred to the glovebox. PEDOT:PSS (AI4083) was spin-coated at 4500 rpm for the 40s and dried for 10 min at 140 ◦C in air. Poly-tbd (5mg/ ml in chlorobenzene) was spin-coated onto the PEDOT:PSS layer at 4000rpm for 40s followed by annealing at 120 ◦C for 5 minutes.
The perovskite nanocrystals dispersed in octane (5mg/ml) were deposited on the substrate by spin-coating at speed of 2000 rpm for 20 s .
Finally, TPBi (60 nm), LiF (1 nm) and Al (100 nm) were sequentially deposited by thermal evaporation under 5 × 10–7 Torr. The full structure of the device was : ITO/PEDOT:PSS/Poly-tbd /perovskite/TPBi/LiF/Al.
Figure. 1(a) Schematic diagrams of the deposition of colloidal solution onto the ITO- glass substrate. (b) CsPbBr3 films covered with epoxy. (b) Energy levels of the device structure of the Peled. (c) Photograph of the emitting intensity of the Peled. ( e) Electroluminescence spectra of fabricated Peled devices.
Characterization
The UV-vis absorption spectra were obtained by Varian 5E UV/VIS/NIR spectrophotometer. X-ray diffraction (XRD) was conducted using an X’Pert-MPD diffractometer (Philips, Netherlands). Photoluminescence (PL) spectra were measure using Photon Technology International Flourometer (PTI, USA). Fourier Transform Infra-Red Spectroscopy (FTIR) was measured using JASCO(FT-4100). Transmission electron microscopy (TEM) were performed using a Hitachi H-7500. The films for TEM measurement was prepared by diluting colloidal solutions in hexane solution and dropped mesh grid with a pipette and dried in vacuum .
The XPS analysis was performed using KRATOS Analytical system. For measuring XPS, the nanocrystals were spin-coated on glass substrates. Steady-state PL spectra were measured using a F-7000 fluorescence spectrometer (Hitachi, Japan) by photoexciting the samples at 375 nm. The current J− V− L curves of the PeLEDs were measured using a Keithley 2450 source measure unit combined with a UVIS-50 spot photodetector.