Materials: Tin chloride dehydrate (SnCl2.2H2O), cesium iodide (CsI), BCP (Bathocuproine), ethanol (99.8%), 4-tert-butylpyridine (TBP), Li-bis (trifluoromethanesulfonyl) imide (Li-TFSI), chlorobenzene, DMSO (Dimethyl sulfoxide anhydrous, ≥99.9% ), and DMF (N,N-Dimethylformamide anhydrous, 99.8%), were purchased from Sigma-Aldrich. Lead (II) Iodide (99.99%, trace metals basis), were purchased from Tokyo Chemical Industry (TCI) Deutschland GmbH. Formamidinium iodide (FAI) and Methylammonium bromide (MABr) and cobalt(III) complex and were purchased from Dyenamo. 2,2’,7,7’-tetrakis--(N,N-di-p-methoxyphenylamine)-9,9’-spirobifluorene (spiro-OMeTAD) (≥99.8%) was purchased from Merk.
Device Fabrication:
Substrate cleaning: Glass/ITO substrates (area of 25 x 25mm, 15 Ω sq-1, 150 nm) were cleaned sequentially by ultra-sonication in mucous solution, deionized water, acetone and isopropanol for 15 minutes each and then lead to UV-O3 treatment for 15 minutes. We fabricated ITO/SnO2/ Cs0.05FA0.79MA0.16PbBr0.51I2.49 /Spiro-OMeTAD/Au hybrid perovskite solar cells. At first, SnO2 ETL was deposited via spin coating technique on cleaned glass/ITO substrate following the same procedure described in our previous reports [34-37]. The SnO2 layer thickness was obtained ~ 25nm confirmed by cross section SEM measurements.
Perovskite inks preparation: Triple cation (Cs0.05FA0.79MA0.16PbBr0.51I2.49) perovskite ink with the final concentration of 1.24M was prepared according to the following cited references (ref of my paper, saliba, etc). In brief, FAPbI3 and MAPbBr3 solutions were prepared via mixing of PbI2 and PbBr2 solutions in FAI and MABr powders respectively. Next, cesium iodide solution was added together with FAPbI3 and MAPbBr3 solutions in a certain ration to realize the final triple cation solution. To make perovskite ink ready for SDC coating, 1.24 M perovskite solution was further dissolved in GBL solution, resulting in different concentrations of the perovskite inks.
Slot die coated perovskite solar cells: At first, perovskite inks were filled in the syringe which is connected to the slot head via a tube. The flow rate of perovskite ink was controlled by pump, pushing the syringe with applied pressure. The temperature of the SDC chuck is controlled via software. The chuck speed is varied from 100-500 cm/min with the flow rate of 0.1 ml/min and 0.2-0.3 mm gap between slot die head and substrate in inert atmosphere. The SnO2 coated substrates were placed at different temperatures (ranging from 50-200 °C) on the chuck and perovskite inks with different concentrations (ranging from 0.6-1M) were spread over the substrate using the coating blade. The perovskite thin films were annealed at 100 °C for 30 minutes. As HTL, spiro-OMeTAD precursor with 36.2 mg/ml concentration dissolved in chlorobenzene and doped with TBP (14.4µL/mL), LiTFSI (8.8µL/mL), and cobalt(III) complex (14.5µL/mL) was spin coated on the SDC prepared perovskite film by spin coating at 1800 rpm for 30 seconds. At last, 80nm thick gold electrodes were thermally deposited over the spiro-OMETAD through shadow masks with the active areas of 0.16 cm2 at a pressure of ̴ 9x10-6 mbar.
Characterization
Device measurements: The J−V measurements of PSCs devices were performed under continuous stimulated AM1.5G 100 mW/cm2 illumination in inert atmosphere using Oriel LCS-100 class ABB solar simulator, calibrated with silicon reference cell (Fraunhofer ISE). A digital source meter (Keithley model 2400) was used to scan J−V curves and MPPT with the LabVIEW code programmed. We have used metal mask with the active area of 0.09 cm2 to measure the PSCs precisely, nullifying the unwanted contribution of current which may due to the area mismatching. The dark J-V curves were also measurement. The delay time, integration time and voltage step, for data point scans were fixed at 20 ms, 40 ms, and 20 mV respectively in both forward(“F”: V £ 0V – short circuit - towards V ³ VOC) and reverse scan(“R”: V ³ VOC scan directions towards V £ 0V) scan directions.
The EQE: External quantum efficiency measurements were carried out using Oriel Instruments QEPVSI-b system with a Xenon arc lamp (Newport 300 W, 66902) chopped at 35.5 Hz and a monochromatic instrument (Newport Cornerstone 260)[38].
Scanning electron microscopy: SEM images (top view and cross-section) were measured by Hitachi S-4100 at 5 kV.
In-situ GIWAXS: In situ grazing incidence wide-angle X-ray scattering measurements were performed at KMC-2 beamline[39] at the synchrotron source BESSY II at Helmholtz-Zentrum Berlin (HZB) berlin Germany. Incident angle was fixed at 2 deg. The photon energy of the source is 8048 eV.
Small angle X-ray scattering:
The SAXS data were taken using synchrotron radiation at the four crystal monochromator beamline in the laboratory of PTB (Physikalisch-Technische Bundesanstalt) at BESSYII[1]. The two-dimensional scattering images were collected by a windowless Dectris 1M PILATUS2 in-vacuum hybrid-pixel detector. The samples were measured at a distance of 0.8 m at photon energy of 10 keV. To ensure a sample-sensitive measurement the solutions were measured with an exposure time of 600 s with two repetitions. Due to the low transmittance of the lead containing precursor solutions, especially thin (0.1 mm), rectangular borosilicate cuvettes purchased from CM Scientific, UK were used.
For data reduction as well as for the radial averaging to the 1D scattering pattern the BerSAS software was used, programmed by Uwe Keiderling.
Rheology of perovskite ink:
Dynamic viscosity was measured with an Automated Micro Viscometer (AMVn) from Anton Paar. A cleaned capillary (∅ = 1.6 mm) was filled under ambient conditions with a stainless steel ball (𝜌 = 7.62 g/cm³; ∅ = 1.5 mm) and the sample solution. The capillary was set to an angle of 70° with respect to the horizon and each measurement was carried out with four repetitions at 20 °C. Wettability measurements were performed with a KRÜSS Drop Shape Analyzer at ambient conditions. Total surface tension was measured by the pendant drop method. The contact angle on a PTFE surface was measured by the static sessile drop method and dispersive and polar part were calculated from it according to OWRK theory. Contact angles on other substrates were measured by the static sessile drop method as well.