Supporting information Spontaneous Passivation of Hybrid Perovskite by Sodium Ions from Glass Substrates - Mysterious Enhancement of Device Efficiency Overtime Discovered Cheng Bi, Xiaopeng Zheng, Bo Chen, Haotong Wei, and Jinsong Huang* Department of Mechanical and Materials Engineering and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0656, USA * To whom correspondence should be addressed-mail: jhuang2@unl.edu Experimental method Perovskite film and device fabrication: Formamidinium iodide (FAI) was synthesized by the method reported elsewhere. 6 In a typical perovskite film fabrication, the substrates (ITO glass, Si, flexible PET/ITO) were treated by UV-ozone (UVO) for 15 min. Then a layer of poly(bis(4-phenyl)(2,4,6- trimethylphenyl)amine) (PTAA) was spun at the rate of 6000 rpm from a 2 mg ml -1 PTAA toluene solution on top of these substrates. For thicker PTAA layers, the concentration increased to 20 mg ml -1 to yield an 80 nm thickness. The as-prepared PTAA films were annealed at 100 C for 10 mins. Thermal annealinginduced interdiffusion method was used to prepare mixed-cation perovskite films. The PbI 2 (99.999% trace metals basis) was dissolved in anhydrous dimethylformamide (DMF) to prepare 680 mg ml -1 precursor solution, respectively. FAI and methylammonium bromide (MABr) was mixed together to form 85:8 mg ml -1 precursor solution in 2-propanol. The FAI: MABr weight ratio was around 10 : 1. The PbI 2 solution was preheated at 90 C and then was spin coated on top of PTAA at 6000 rpm for 30 s. After the as-prepared PbI 2 film dried at 90 C for 5 min, the FAI: MABr mixed precursor solution preheated at 70 C, was spin
coated on top of the PbI 2 layer at a rate of 6000 rpm for 30 s. The stacked precursor layers were dried at 70 C for 15 min. After that, the films were annealed at 100 C for 60 min. The PTAA and perovskite film fabrication and the followed-up annealing were carried out in a glove box filled with nitrogen. To finish the device fabrication, 20 mg ml -1 phenyl-c71-butyric acid methyl ester (PCBM) solution in dichlorobenzene (DCB) was used to spin coat a PCBM layer on top of perovskite film by a rate of 6000 rpm for 30 s. A thermal annealing at 100 C was performed on the as-fabricated films for 60 min. Finally, 20 nm C 60, 8 nm 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) layer and 80 nm copper electrode was sequentially deposited by thermal evaporation. The working area of the device was 8.0 mm 2. Film and device characterization: Quanta 200 FEG environmental scanning electron microscope (SEM) was used to take the images of films surface morphology. Rigaku D/Max-B X-ray diffractometer with Bragg-Brentano parafocusing geometry was used to obtain the perovskite films XRD patterns. A Co-Kα tube was employed with emitted X-ray wavelength of 1.79 Å. Time-resolved photoluminescence (TRPL) was performed on the perovskite films grown on varied substrates by a Horiba DeltaPro fluorescence lifetime system, which equipped with a DeltaDiode (DD-405) pulse laser diode with wavelength of 404 nm. The laser excitation energy in the measurement was 20 pj pulse -1. The lifetime of the perovskite films was obtained by fitting the PL curve with a bi-exponential decay: (1) The lifetime discussed in the report is the slow decay component ꞇ 2. For device J-V curve measurement, the AM 1.5G irradiation (100 mw/cm 2 ) was provided by a Xenon-lamp-based solar simulator (Oriel 67005, 150 W Solar Simulator). Before photocurrent measurement, the light intensity was calibrated by a Si diode (Hamamatsu S1133) equipped with a Schott visible-color glass filter (KG5 color filter). The device photocurrent was recorded by Keithley Model 2400, and the scanning rate was 0.07 V/s for the device J-V curve measurement.
Current density (ma/cm 2 ) The devices tdos was derived from the frequency-dependent capacitance (C~f) and voltagedependent capacitance (C~V), which were obtained from the thermal admittance spectroscopy (TAS) measurement performed by a LCR (inductance (L), capacitance (C), and resistance (R)) meter (Agilent E4980A). The derivation procedure was reported elsewhere. 10,44 The devices were kept under 1 sun illumination at room temperature during the C~f and C~V measurement. For transient photovoltage (TPV) measurement, the device was connected to a digital oscilloscope (DOS-X 3104A) with an input impedance of 1MΩ to form an open-circuit condition. The TPV measurement was performed under one sun illumination and a small perturbation that induced a photovoltage variation smaller than 5% of device s V OC was generated by an attenuated UV laser pulse (SRS NL 100 Nitrogen Laser) with 337 nm wavelength. 0-5 -10-15 -20-25 0.0 0.2 0.4 0.6 0.8 1.0 Voltage (V) Figure S1 Device s J-V curve with different scanning direction; no obvious photocurrent hysteresis. Figure S1 shows the minimized photocurrent hysteresis with change of the photocurrent scanning direction. Minimized photocurrent hysteresis results from high quality and uniform perovskite films formed on nonwetting poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA) surface and passivation by the double fullerene layers.
Current Density (ma cm -2 ) Voc (V) Fill Factor (%) Current Density (ma cm -2 ) 25 24 23 22 Voc (V) 1.10 1.08 1.06 1.04 Fill Factor (%) 0.78 0.75 0.72 0.69 0.66 Time(days) 25 24 23 1.08 1.06 1.04 1.02 0.80 0.76 0.72 0.68 0.64 Figure S2 The evolution of device s J SC, V OC and FF during the storage in inert (upper row) and ambient (lower row) condition. Each curve represents parameter evolution of individual device. Figure S2 summarizes the evolution of device performance during storage. The spontaneous enhancement mainly comes from the increased J SC and FF. This observation is correlated to the passivation of other monovalent metal cations in organic-inorganic hybrid perovskite (OIHP) solar cell where increased J SC and FF were observed after the passivation 3.
a Fresh Day 7 b Day 1 Day 7 Intensity (a.u) 2 um 2 um 10 20 30 40 50 60 2 ( ) Figure S3 X-ray diffraction (XRD) pattern (a) and topography scanning electron microscopy (SEM) image (b) of the as-prepared mix-cation (organic-inorganic hybrid perovskite) OIHP films at day 1 and day 7; The films were stored in inert condition. Figure S3 shows the evolution of perovskite films crystalline and morphology during 1 week storage. Both showed no significant change, which excludes the possible reason of spontaneous enhancement from improved film s crystalline and morphology.
Voltage (V) 1.10 1.09 1.08 1.07 1.06 1.05 TPV Fited curve Under 1 sun illumination 945 ns 0 1 2 3 4 5 6 Time ( s) Figure S4 Photovoltage decay of a device stored in N 2 for 48 hours; The transient photovoltage (TPV) was measured under 1 Sun illumination; The fitted curve derived a lifetime of 945 ns. References 1. Shao, Y.; Xiao, Z.; Bi, C.; Yuan, Y.; Huang, J. Origin and elimination of photocurrent hysteresis by fullerene passivation in CH 3NH 3PbI 3 planar heterojunction solar cells. Nat. Commun. 2014, 5, 5784. 2. Bi, C.; Yuan, Y.; Fang, Y.; Huang, J. Low-Temperature Fabrication of Efficient Wide-Bandgap Organolead Trihalide Perovskite Solar Cells. Adv. Energy Mater., 2015, 5, 1401616. 3. Abdi-Jalebi, M.; Dar, M. I.; Sadhanala, A.; Senanayak, S. P.; Franckevičius, M.; Arora, N.; Hu, Y.; Nazeeruddin, M. K.; Zakeeruddin, S. M.; Grätzel, M.; Friend, R. H., Impact of Monovalent Cation Halide Additives on the Structural and Optoelectronic Properties of CH 3NH 3PbI 3 Perovskite. Adv. Energy Mater., 2016, 6, 1502472.