Keithley 2400

The morphology and size distribution of the NRs were observed using field emission scanning electron microscopy (FE-SEM, JEOL, JSM7000F) operated at 15 kV. The crystallographic information was obtained by X-ray diffraction (XRD, Bruker-AXS, D8 Discover) and the chemical bonding structure was analyzed through X-ray photoelectron spectroscopy (XPS, VG Microtech, ECSA2000) using Al Kα. A Shirley function was used to subtract the background and all the spectra were fitted by using a Gaussian–Lorentz function, i.e. Gaussian/Lorentz = 80/20. The optical property was measured using cathode-luminescence (CL) spectroscopy (GATAN, MONO CL³⁺) at room temperature. The current-voltage (I-V) measurement of the n-ZnO NRs/p-GaN heterojunction LEDs was performed with a semiconductor parameter analyzer (Agilent, B1500A) and the EL property of the LEDs was evaluated using voltage/current source meter (Keithley Instruments, Keithley 2400) and UV-visible spectrophotometer (Ocean optics, USB 4000). The EL spectra were smoothed by using Savitzky-Golay algorithm and were finally normalized to the maximum value.

The current density–voltage–luminance characteristics and EL spectra were measured with a custom-built system^{43 (link)} consisting of a digital source meter (Keithley 2400) and an integrating sphere (FOIS, Ocean Optics) coupled to a spectrometer (QE Pro, Ocean Optics). The operational lifetimes of the LEDs were measured using a commercial LED lifetime test system (Guangzhou Crysco Equipment). The temperature-dependent EQEs were measured using a device test box consisting of a silicon photodiode and a semiconductor temperature control system (Guangzhou Crysco Equipment). The angle dependence of the emission intensity of the LED was measured using a photodetector (PDA100A, Thorlabs) at a fixed distance of 200 mm from the LED.

ITO coated glass substrates were treated with detergent overnight and then by TL1 (NH₃: H₂O₂: H₂O = 1:1:5) procedure for 20 min. ZnO nanoparticles were deposited in ambient condition by spin coating at 4000 rpm for 40 s and annealed at 150 °C for 30 mins. PEIE dispersed in IPA solution with a concentration of 0.05 wt% was spin coated on the top of ZnO at 5000 rpm for 40 s. Perovskite based solutions, with and without starch, were spin-coated on ITO/ZnO/PEIE in glovebox at 7000 rpm for 100 s and then the films were annealed at 100 °C for 10 min. TFB solution (8 mg/ml in m-xylene) was spin-coated onto the perovskite film. Finally, 10 nm of MoO₃ film and 100 nm of Ag film were deposited as electrode inside of the thermal evaporator.
The performances of all the Perovskite LED devices were measured in a nitrogen-filled glovebox at room temperature. A Keithley 2400 was used to collect current density and driving voltage data and an integrating sphere together with the Go pro spectrometer (Ocean Optics) were used to collect emission data. The device working area is 0.0725 cm².