GoKawiilMaterials
Cesium bromide (CsBr, 99.999%), lead bromide (PbBr 2 , 99.999%), lead chloride (PbCl 2 , 99.999%), PVP (Mw 60,000), 4,7,10-trioxa-1,13-tridecanediamine (TTDDA, 97%), PVK (Mn 25,000–50,000), lithium fluoride (LiF, 99.99%), dimethyl sulfoxide (DMSO, 99.9%), N,N-dimethylformamide (DMF, 99.8%), chlorobenzene (CB, 99.8%), 2-propanol (IPA, 99.5%) were purchased from Sigma Aldrich. Formamidinium bromide (FABr) was purchased from Greatcell Solar Materials. 2,2′,2′′-(1,3,5-Benzinetriyl)-tris(1-phenyl-1H-benzimidazole) (TPBi) and PTAA were purchased from Ossila.
Preparation of the perovskite solution
Perovskite precursors (CsBr:FABr:PbBr 2 :PbCl 2 :TTDDA ratio of 1.2:0.3:0.3875:0.6125:0.1) were dissolved in DMSO with a Pb concentration of 0.1 M. Precursor solutions were stirred at 65 °C before spin-coating.
PeLED fabrication
ITO substrates were cleaned with deionized water, acetone and isopropanol for 15 min, followed by an ultraviolet ozone treatment for 20 min and then were transferred into a nitrogen-filled glovebox. PTAA and PVK were deposited in sequence on the ITO substrates and annealed at 120 °C and 100 °C for 10 min, respectively. Then, a thin layer of PVP was deposited and annealed at 80 °C for 10 min. All the above-mentioned HTLs were spin-coated at a speed of 4,000 rpm for 30 s. Finally, the perovskite precursor was spin-coated at 4,000 rpm for 40 s. Immediately after spin-coating, the films were transferred into an enclosed petri dish with 20 μl DMF. After DMF treatment for a certain time, the perovskite films were annealed at 80 °C for 8 min. Then, all the substrates were loaded into an evaporator with a pressure of 10−6 mbar for evaporation. Then, 50 nm TPBi, 1.5 nm LiF and 100 nm Al were deposited with shadow masks via thermal evaporation. The active area of the LEDs is 4.5 mm2.
PeLED characterization
PeLED device current density–voltage–luminance measurements were carried out in atmosphere with encapsulation. The current density–voltage–luminance characteristics were measured using a Keithley 2400 source meter and a calibrated silicon photodetector for luminance calibration. The LED metrics were calculated considering the responsivity of the silicon photodetector. The electroluminescence spectra were obtained using an Ocean Optics Flame spectrometer.
Steady-state photoluminescence
Photoluminescence was measured using an Edinburgh FLS1000 spectrometer with an excitation wavelength at 405 nm. The spectrum was captured with a step of 1 nm and an exposure time of 0.2 s at each wavelength.
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