Supporting information Improvement of Transparent Conducting Performance on Oxygen- Activated Fluorine-Doped Tin Oxide Electrodes Formed by Horizontal Ultrasonic Spray Pyrolysis Deposition Bon-Ryul Koo, Dong-Hyeun Oh, Doh-Hyung Riu,,,, and Hyo-Jin Ahn,, Program of Materials Science & Engineering, Convergence Institute of Biomedical Engineering and Biomaterials, Department of Materials Science and Engineering, Seoul National University of Science and Technology, Seoul 01811, Korea and Research Institute for FTO, ceon Co., Ltd., Suwon-si, Gyeonggi-do, 16642, Korea Corresponding author. E-mail address: dhriu15@seoultech.ac.kr (D.-H. Riu) Corresponding author. E-mail address: hjahn@seoltech.ac.kr (H.-J. Ahn)
EXPERIMENTAL SECTION Highly transparent conducing FTO electrodes were fabricated using the HUSPD. The precursor solution for the HUSPD was prepared by dissolving 0.68 M tin chloride pentahydrate (SnCl 4 5H 2 O, SAMCHUN) and ammonium fluoride (NH 4 F, Aldrich) in deionized (DI) water with 5 vol% ethyl alcohol (C 2 H 5 OH, Duksan). To obtain the optimum performance of the FTO electrode, the mole ratio of F/Sn was fixed at 1.765 15. Furthermore, this solution was sprayed onto the glass substrate (Corning EAGLE XG TM ) maintained at 420 C by using an ultrasonic atomizer (1.6 MHz), in which the rotation speed of substrate was fixed at 5 rpm. The flow rate of the carrier gas and spraying time of solution were applied to 15 L/min and 23 min, respectively. At this time, in order to investigate the effect of oxygen activation in the fabrication of the FTO electrodes (herein designated as FTO-0% O 2, FTO-20% O 2, and FTO-50% O 2 ), the ratio of O 2 to (O 2 +N 2 ) in the carrier gas was controlled to be 0, 20, and 50%. After spraying, all electrodes were naturally cooled down, finally fabricating three types of the FTO electrodes using the HUSPD. The prepared FTO electrodes were used as a TCE of both working and counter electrodes in DSSCs. To fabricate the working electrode, TiO 2 paste was prepared by mixing P25 (DEGUSSA), hydroxypropyl cellulose (HCP, M w = 80,000 g/mol, Aldrich), and acetylacetone (C 5 H 8 O 2, Aldrich) with deionized water. Then, a uniformly mixed TiO 2 past was squeeze-printed on the FTO electrodes. After calcination at 500 C, the TiO 2 paste-coated FTO electrodes were immersed into a dye solution with 0.5 mm N719 (Ru(dcbpy) 2 (NCS) 2, Solaronix) and ethanol (C 2 H 6 O, Aldrich) for 24 hr in a dark room. For the counter electrodes, 5 mm Pt solution dissolved chloroplatinic acid hexahydrate (H 2 PtCl 6 6H 2 O, Aldrich) in 2- propanol ((CH 3 ) 2 CHOH, Aldrich) was spin-coated onto the FTO electrodes and then was calcined at 450 C for 30 min. Finally, DSSCs were assembled by overlapping the working and counter electrodes as sandwich-type cells and then filled with a 0.6 M BMII (1-Butyl-3-
methylimidazolium iodide)-based iodine solution as an electrolyte into the narrow space between two electrodes. Thereafter, the structural properties of electrodes were investigated by X-ray diffraction (XRD, Rigaku D/Max-2500 diffractometer using Cu K radiation). The surface morphology of the FTO electrodes was characterized using field-emission scanning electron microscopy (FESEM, Hitachi S-4800) and atomic force microscopy (AFM, didimension TM 3100). The chemical binding state of the electrodes was recorded using X-ray photoelectron spectroscopy (XPS, ESCALAB 250 equipped with an Al K X-ray source) and Fourier transform infrared (FTIR) spectroscopy (Thermo Flsher Scientific, Nicolet is50). The electrical and optical properties were characterized by a Hall-effect measurement system (Ecopia, HMS-3000) and ultraviolet-visible (UV-vis) spectroscopy (Perkim-Elmer, Lambda- 35), respectively. The photovoltaic performances of the DSSCs were measured using a solar simulator equipped with a 150 W xenon arc lamp (Peccell Technologies, PEC-L01) under the light intensity of 100 ma/cm 2. The measurement of electrochemical impedances on the cells was performed using Potentiostat/Galvanostat (PGST302N, Eco chemie) with an AC signal of 10 mv in the frequency range from 100 khz to 0.1 Hz.
Figure S1 AFM images of (a) FTO-0% O 2, (b) FTO-20% O 2, and (c) FTO-50% O 2.
Figure S2 XPS core-level spectra of (a c) F 1s and (d f) O 1s measured from FTO-0% O 2, FTO-20% O 2, and FTO-50% O 2.
Figure S3 FTIR result of (a) FTO-0% O 2, (b) FTO-20% O 2, and (c) FTO-50% O 2.
In( ) (cm -1 ) 11.0 10.5 FTO-0% O 2 : 423.0 mev FTO-20% O 2 : 390.3 mev FTO-50% O 2 : 378.5 mev 10.0 9.5 4.0 4.1 4.2 4.3 4.4 Photon energy (ev) Figure S4 Calculation of the Urbach energy for all samples.
Figure S5 Plot of (αhν) 2 versus photon energy obtained from FTO-0% O 2, FTO-20% O 2, and FTO-50% O 2.
Figure S6 Absorption spectra of the FTO-TiO 2 -dye working electrode composited of dyeabsorbed TiO 2 and the prepared FTO electrodes.
Table S1 Summary of atomic percentages obtained from O, Sn, and F elements for all the samples. Atomic percentages FTO-0% O 2 FTO-20% O 2 FTO-50% O 2 O (at%) 67.6 67.4 68.6 Sn (at%) 30.4 30.3 28.6 F (at%) 2.0 2.3 2.8
Table S2 List of electrical and optical properties for the FTO electrodes obtained from various processes. Processes ρ 10-4 (Ω cm) μ (cm 2 /V s) N 10 20 (cm - 3 ) T (%) Φ 10-2 Ω -1 Spray pyrolysis 1 23 5.7 30.0 3.70-3.10 Spray pyrolysis 2 53 6.2 18.0 6.21 77 - Spray pyrolysis 3 26 3.0 35.0 6.00 81 - Spray pyrolysis 4 54 6.0 28.0 2.00 92 3.10 Chemical vapor deposition 20 4.0 39.0 4.00 80 - Sputtering 19 3.7 3.8 4.39 80 - Pulsed laser deposition 21 5.0 - - 87 - Horizontal ultrasonic spray pyrolysis (Our work) 2.3 40.7 6.62 85.3 5.09