Co-Cation Engineering via Mixing of Acetamidinium and Rubidium in FASnI3 for Tin Perovskite Solar Cells to Attain 14.5% Efficiency

Tin perovskite solar cells (TPSCs) were developed by adding the co-cations acetamidinium (AC) and rubidium (Rb) in varied proportions based on the FASnI3 structure (E1). We found that adding 10% AC and 3% Rb can optimize the device (E1AC10Rb3) to attain an efficiency of power conversion of 14.5% with great shelf- and light-soaking stability. The films at varied AC and Rb proportions were characterized using XPS, SEM, AFM, GIWAXS, XRD, TOPAS, TOF-SIMS, UV–vis, PL, TCSPC, and femtosecond TAS techniques to show the excellent optoelectronic properties of the E1AC10Rb3 film in comparison to those of the other films. AC was found to have the effect of passivating the vacancy defects on the surface and near the bottom of the film, while Rb plays a pivotal role in passivating the bottom interface between perovskite and PEDOT:PSS. Therefore, the E1AC10Rb3 device with a band gap of 1.43 eV becomes a promising candidate as a narrow band gap device for tandem lead-free perovskite solar cell development.

thickness ~35 nm) and a hole-blocking layer (BCP, thickness ~5 nm) was deposited using a thermal evaporation machine.Finally, a top metal layer composed of silver (Ag) with a thickness of approximately 100 nanometers was deposited onto the structure through thermal evaporation under a vacuum pressure of about 5×10⁻⁶ Torr.

Characterization of films and devices:
The photovoltaic characteristics of the devices were determined using a Keithley 2400 meter under standard solar illumination conditions (AM 1.5G, intensity of 100 mW per square centimeter), provided by a solar simulator (XES-40S1, .This process involved calibrating with a silicon solar cell equipped with a KG-5 filter.All photovoltaic measurements, including reverse scans from open-circuit voltage to 0 volt and forward scans from 0 volt to open-circuit voltage, were performed in normal air conditions.During these tests, a metal mask of 0.1 square centimeter area was used to cover the device.The conversion efficiency of photons to electrons (IPCE) was measured with an apparatus comprising a Xenon lamp (A-1010, PTi, 150 watts) and a monochromator (PTi, 1200 grooves per millimeter, optimized for 500 nanometers wavelength).Calibration of the IPCE spectra was conducted using a standard silicon photodiode (S1337-1012BQ, Hamamatsu brand).X-ray diffraction patterns were obtained using a Bruker D8-Advance diffractometer with copper K-alpha radiation.To examine the morphology and structure of the samples, a high-resolution Scanning Electron Microscope (SEM, Hitachi SU8010 model) and an Atomic Force Microscope (AFM, VT SPM model from SII Nanotechnology Inc.) were utilized.The samples were sealed with a glass cover using UV-sensitive adhesive (NOA 68, Norland Products).
UV-visible absorption spectra for the perovskite samples were recorded using a Jasco V780 UV-visible spectrophotometer.Photoluminescence (PL) spectra were acquired using a Continuous Wave diode laser (450 nm wavelength, MDL-III-450-100 mW model; with PSU-III-FDA power supply) as the excitation source.Emission spectra were collected in the 550-1100 nm range using a Dongwoo DM150i spectrometer with 600 grooves optimized for 750 nm, and detected with a thermoelectrically-cooled silicon photodiode (Sciencetech Inc.S-025-TE2-H; powered by a PS/TC-1 supply).

TCSPC measurements:
Time-Correlated Single Photon Counting (TCSPC) measurements were conducted utilizing a TCSPC setup (Fluotime 200, Picoquant brand), which used a laser with an excitation wavelength of 635 nanometers.These measurements focused on capturing transient decay profiles at the peak wavelengths observed in the PL spectra.Throughout these experiments, the laser operated at a consistent repetition rate of 25 MHz, and its pulse energy was maintained at 4 microjoules per square centimeter.The collected transient PL profiles were then meticulously analyzed and interpreted using a bi-or triexponential function model to understand their decay characteristics.

Grazing-incidence Wide-angle X-ray Scattering (GIWAXS) measurements:
Grazing Incidence Wide Angle X-Ray Scattering (GIWAXS) studies were carried out at the TPS 25A1 beamline station, located at the National Synchrotron Radiation Research Center (NSRRC) in Taiwan.The X-ray beam used in these experiments had a photon energy of 12.37 keV and its dimensions were finely tuned to 5 m by 5 m.By setting the incident angle of the X-ray beam to a minimal 0.05 degree, the area of the beam interacting with the samples was restricted to a span of just a few mm.The experiments were designed with a distance of 85 mm between the sample and the detector, allowing for a measurement range (q-range) extending from 0.1 to 5 Angstroms inverse.This setup, combining a low angle of incidence with a small beam footprint, significantly improved the clarity of the film diffraction patterns.These patterns were then precisely recorded using the Eiger X 1M single-photon counting detector, which features a pixel size of 75 m.

Time-of-flight secondary-ion mass spectroscopy (TOF-SIMS) measurements:
Depth profiles using Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) were acquired with a PHI TRIFT V nanoTOF system (manufactured by ULVAC-PHI, Japan), utilizing a dual beam technique that combines slicing and viewing.The data collection process involved the use of a pulsed C60 + primary ion beam, set at an energy of 20 kV, with a pulse frequency of 8200 Hertz and a pulse duration of 15 ns, which was instrumental in generating secondary-ion signals.This primary ion beam maintained a current of 0.15 nA (DC).The targeted area for analysis was defined as 50 m by 50 m.To accelerate the secondary ions, a 3 kV bias was applied to the sample.
During the data acquisition process, both a 10 V electron flood and a 10 V Ar + flood were used to neutralize any surface charge.In order to compensate for variations in the primary ion signal, all secondary-ion signals within the depth profiles were normalized against the total ion signals.For the sputtering phase, aimed at removing material from the surface, a 1 kV Ar + ion beam with a current of 100 nA (DC) was utilized.The raster area designated for this Ar + sputtering beam was 2 mm by 2 mm.

Femtosecond transient absorption spectral (TAS) measurements:
Femtosecond transient absorption spectra were collected with the Excipro transient absorption spectrometer (manufactured by CDP systems), as detailed in previous reports.The process involved exciting the samples with a 532 nm pump pulse, with a duration of approximately 70 fs, and then probing them in the wavelength range of 570 to 980 nm using a white light supercontinuum probe pulse.The laser fluence at the sample location was estimated to be around 4 J per square centimeter.To protect the samples from atmospheric elements and laser-induced damage, they were encaspsulated and continuously rotated throughout the measurement process.The data gathered was then refined by correcting for the chirp and reducing noise through the

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Figure S1.J-V measurements of TPSC devices made on different ratios of AC.

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Figure S2.J-V measurements of TPSC devices made on different ratios of Rb.

Figure S7 .
Figure S7.TOPAS fitting of the E1 sample.The shadow area indicates the signals from ITO substrate.

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Figure S8.TOPAS fitting of the AC5 sample.

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Figure S9.TOPAS fitting of the AC10 sample.

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Figure S11.TOPAS fitting of the AC20 sample.

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Figure S12.TOPAS fitting of the AC40 sample.

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Figure S14.TOPAS fitting of the Rb2 sample.

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Figure S15.TOPAS fitting of the Rb3 sample.

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Figure S17.TOPAS fitting of the Rb10 sample.

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Figure S21.UPS raw data of the E1AC20-98 samples.

Figure S25 .
Figure S25.Boxplots of photovoltaic parameters for the devices made of E1, E1AC10 and E1AC10Rb3.

Figure S26 .
Figure S26.Device performance of the E1AC10Rb3 device measured under one-sun ambient air condition (relative humidity = 50%) at maximum-power point (MPP) for continuous irradiation up to 7.5 h.

Table S2 .
Lattice parameters of the AC samples obtained from TOPAS simulations.

Table S3 .
Lattice parameters of the Rb samples obtained from TOPAS simulations.

Table S6 .
Raw data of photovoltaic parameters for the E1 devices.

Table S7 .
Raw data of photovoltaic parameters for the E1AC10 devices.