Materials: CsI, PbI2, LiF, dimethyl sulfoxide (DMSO), ethyl acetate (EA), chlorobenzene and poly (sodium 4-styrenesulfonate) (PSS-Na, average Mw ~ 70000) were purchased from Sigma-Aldrich. TPBi, PEAI, m-F-PEA, NMAI and PVK (average Mw >100000) were purchased from Xi’an Polymer Technology Corp. Poly-TPD was purchased from 1-Material. And the m-PEDOT: PSS solution was a mixture of normal PEDOT: PSS (AI 4083) aqueous solution with 100 mg∙ml-1 PSS-Na aqueous solution by a volume ratio of 6: 5.
Perovskite Precursor Synthesized: The quasi-2D perovskite (PEA)2CsPb2I7 precursor was prepared by dissolving PEAI, CsI, and PbI2 in a molar ratio of 1:0.75:1 in DMSO under continuous stirring overnight at 40 °C, keeping the molar concentration Pb2+ at 0.5 M. And ((PEA/m-F-PEA)xNMA1-x)2CsPb2I7 precursor was prepared by mixing PEA/m-F-PEA and NMA in a molar ratio of x: 1-x on the basis of single-cation perovskite (x = 0, 0.2, 0.4, 0.6, 0.8 and 1).
Device Fabrication: Indium tin oxide (ITO)-coated glass substrates were sequentially cleaned in detergent, deionized water, acetone, isopropyl alcohol. Then dry it with nitrogen and treat it with ultraviolet ozone for 20 minutes. The m-PEDOT: PSS aqueous solution was spin-coated at 7000 rpm for 40 s, followed by drying at 160 °C for 15 min in ambient air. Then, the samples were transferred into a nitrogen-filled glovebox, spin-coating poly-TPD (10 mg/ml in chlorobenzene) and PVK (2.5 mg/ml in chlorobenzene) on the m-PEDOT: PSS substrate at 2000 rpm for 40 s in turn, and annealing at 150 °C for 30 min. The RPP films were fabricated by spin-coating the precursor solutions at 9000 rpm for 60 s, and after spin-coating for 15 s, 120 μL of EA was poured onto the film as an anti-solvent, followed by annealing at 80 °C for 15 min. Finally, the TBPi layer (30 nm) and LiF/ Al electrodes (1 nm/100 nm) were deposited through a shadow mask in a high vacuum of ~ 1×10–4 Pa thermal evaporator. The device active area was 0.1 cm2 as defined by the overlapping area of the ITO and Al electrode.
Film and Device Characterization Measurement: Absorption spectra were measured using a UV–vis spectrometer (Cary 5000). PL spectra and TRPL were acquired at room temperature in the ambient air using a FLS1000 spectrometer with excitation at 375 nm from a 450 W Xenon lamp and the estimated light power density incident on the samples was about 3.5 mW∙cm−2. PLQYs of the perovskite thin films were recorded by a commercialized PLQY measurement system (LQE-50-PL) from Enlitech with excitation from a 368 nm LED. The XRD patterns of the perovskite thin films were performed with a Rigaku D/max 2500H equipment with a conventional Cu target X-ray tube (Cu K-alpha, λ = 1.5405 Å), with X-ray generator settings at 40 kV and 30 mA. The GIWAXS was performed at BL17B1 beamline of SSRF using the X-ray energy of 10KeV. Two-dimensional patterns were acquired by a PLATUS 2M detector mounted vertically at a distance ~240 mm from the sample with a grazing incidence angle of 0.2º or 0.4 º and an exposure time of 20 sec. The TA measurement was carried out by a homebuilt spectroscopy setup, with the laser source of a commercial femtosecond amplifier laser system (70 fs, 2 kHz, 800 nm, Solstice, Spectra Physics) and the collection device of a laser frequency synchronized fiber optical spectrometer (AvaSpec-ULS2048CL-EVO, Avantes). The output pulse was split into two beams. The first beam was used to pump a commercial optical parametric amplifier (TOPAS prime, Spectra Physics) and frequency converter to provide a frequency tunable femtosecond laser source. The second beam with weaker energy was focused into a CaF2 plate (4 mm thickness) to generate a white light continuum as the probe. During the experiment, UV femtosecond laser pulses centered at 340nm was used and the pump intensity was set to be 12 uJ∙cm-2. XPS was performed on ESCALab 250Xi of Thermo Scientific using 200 W monochromated al Kα (1486.6 eV) radiation and adopting 500 μm X-ray spot to analyze XPS while the analysis chamber bottom pressure ~ 3 ×10−10 mbar. Typically, the hydrocarbon C 1s line is formed from amorphous carbon at 284.8 eV for reference energy. AFM measurements were carried out by a Bruker FASTSCANBIO in non-contact mode. The SEM images were carried out by a field-emission SEM (FEI NanoSEM650), which used an electron beam accelerated at 500 V to 30 kV. TEM was carried out with a JEOL JEM-2100F, operated at 200 kV.
The EQE, I-V-L curve, EL spectrum, CIE, and operating lifetime of the perovskite LED were carried out simultaneously by a commercialized system (LQE-50-EL, Enlitech) with an integrated sphere and photomultiplier tubes (PTM), which is used to measure the low luminance, and all electrical tests are conducted at room temperature in the ambient air for the un-encapsulated devices.