Supporting Information. Far-UV Annealed Inkjet-Printed In 2 O 3. Semiconductor Layers for Thin-Film Transistors on

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1 Supporting Information Far-UV Annealed Inkjet-Printed In 2 O 3 Semiconductor Layers for Thin-Film Transistors on a Flexible Polyethylene Naphthalate Substrate Jaakko Leppäniemi*, Kim Eiroma, Himadri Majumdar and Ari Alastalo VTT Technical Research Centre of Finland, Ltd. Tietotie 3, FI Espoo, Finland jaakko.leppaniemi@vtt.fi S-1

2 Scheme S1: Possible photodecomposition processes yielding hydroxyl radicals during the far UV (~160 nm) exposure of the In 2 O 3 precursor ink. 1 3 Figure S1: Viscosity measured at 10 k (1/s) shear rate and surface tension measured at ~21 C for the In 2 O 3 inks with varied ethylene glycol (EG) co-solvent ratio with corresponding line fits to the data. Stability metric for inkjet-printing: The stability of the inkjet-printing process was studied using a conventional fluid parameter calculation for the droplet formation and using a printed droplet matrix for the printing result. A host of interrelated, dimensionless parameters based on the physical properties of the printable fluid have been used to estimate stable droplet formation conditions in inkjet-printing. 4 Those include the Weber ( ), Reynolds ( ), and Ohnesorge ( ) numbers. We used so-called value for assessing the droplet formation stability, which is defined as the inverse of the Ohnesorge number = 1 = ( ) = ( ) where,, and are the density, surface tension, and viscosity of the fluid. is the characteristic length, i.e the nozzle diameter (here 21 µm). The and were obtained from the line fits to the data shown in Figure S1. The was calculated based on the co-solvent percentage by mass ( ) and the density of the solvents g/cm 3 and g/cm 3 for 2- methoxyethanol and ethylene glycol, respectively., S-2

3 In order to get a quantitative estimation for the inkjet-printing process stability also in terms of the printing result, a droplet matrix having a drop spacing of 225 µm was printed on Si/SiO 2 - substrate using the inks with different co-solvent ratio. From the optical microscope images containing 10 x 10 droplets shown in Figure S2, software written in Matlab automatically mapped the center points of the droplets and their diameter. The software also calculated the variation in the center-to-center distance of the droplets using the vector shown in Figure S2 (f). As the center-to-center distance of adjacent droplets in -direction inside each row is mainly affected by the speed of the substrate plate during the printing and the droplet firing frequency (1 khz), the vector was selected between the center points of the droplets in adjacent rows. Thus for the center-to-center distance in the -direction, the -projection of = was used, and for the center-to-center distance in the -direction, the -projection of = was used. To obtain a single value stability metric, the average center-to-center distance and its standard deviation was calculated among the set containing all values of and (81 points). For the stability metric, we used the inverse of the standard deviation ( ). Table S1. Ink properties for the inks with varied EG weight-ratio ( ): solid-content for the In(NO 3 ) 3 hydrate ( ), ink molarity ( ), printed film thickness after annealing measured with stylus profilometer ( ), or with AFM ( ), average roughness measured with AFM over 10 µm x 10 µm scan area ( ), number of measured TFTs ( ), calculated saturation mobility ( ), threshold voltage ( ), and hysteresis in transfer curve ( ). (wt%) (wt%) (M) (cm 2 /Vs) (V) (V) ± 2 11 ± ± ± ± ± 3 12 ± ± ± ± ± 3 10 ± ± ± ± ± 3 7 ± ± ± ± ± 3 6 ± ± ± ± ± ± ± ± 0.2 S-3

4 Figure S2. Optical microscope images of the 10 x 10 droplet matrix used to calculate the stability metric for the inkjet printing process for (a) the base solution without EG ( = 0 %) and the inks with (b) = 5 %, (c) = 10 %, (d) = 20 %, and (e) = 30 %. (f) Droplet center-point detection using the software and the center-to-center vector used for the calculation of the deviation in the centerto-center distances. S-4

5 Figure S3. Optical microscope images of TFTs on Si/SiO2 substrate inkjet-printed using the ink with (a) = 5 %, and (b) = 30 %. The red dashed area shows the area of the close-up shown in (c) and (d). Figure S4. AFM scans over 10 µm x 10 µm scan area and the calculated average density ( ) for films inkjet-printed using the ink with (a) = 0 % (0.10 M), (b) = 0 % (0.20 M), (c) = 5 % (0.2 M), (d) = 10 % (0.19 M), (e) = 20 % (0.17 M) and (f) = 30 % (0.15 M). S-5

6 Figure S5. XRR measurements for (a) the Si/SiO 2 substrate, and the In 2 O 3 films annealed at (b) 300 C in air for 30 min, (c) 200 C in air for 30 min, (d) 150 C + FUV for 30 min, (e) 150 C + FUV for 180 min, and (f) 200 C + FUV for 30 min. The gray dotted lines in (b) (f) denote the curve fits (in the = range) using the two layer model shown in Figure S6. S-6

7 Figure S6. Two layer model for XRR curve fitting and parameters used in the data fits. Two layer model for XRR curve fitting: The curve fitting for the XRR data was performed using a software tool following the fitting procedure developed by Tiilikainen et al. 5 A two layer model was used to fit the XRR data, where the annealed In 2 O 3 layer was sectioned in lower bulk and top layers, as shown in Figure S6, and assuming a stoichiometric condition for the both layers. The two layer model gave substantially improved curve fitting compared to a single In 2 O 3 layer model. The two layer model can be understood to represent different electron density at the interface of the SiO 2 substrate ( bulk ) and at the top interface exposed to air ( top ). 6 In reality, the In 2 O 3 film can have a density gradient rather than two films of different density. Notably all films show a higher density at the top ( ) than in the bulk ( ) of the In 2 O 3 film. For the FUV annealed films, a higher density at the top could be expected to arise from the enhanced condensation process by the absorbed FUV quanta. Earlier, also spin-coated and thermally annealed metal oxide films obtained from nitrate-based aqueous solutions have shown to exhibit an inhomogeneous density profile with a high density crust at the top of the metal oxide layer along with an increased concentration of heavy metal atoms. 6 However, to detect such changes in the chemical structures, analysis techniques complementing XRR would be required. To get a single density value we calculated the average value for the density of the In 2 O 3 films using = +, where the and are the thickness of the top and bulk layer, respectively, and =. S-7

8 Table S2. Parameters obtained from the curve fitting of a two layer model to the XRR data. FUV,, ( C) (min) (g/cm 3 ) (g/cm 3 ) (g/cm 3 ) 150 yes yes yes no no S-8

9 Figure S7. Output curves of inkjet-printed In 2 O 3 TFTs on Si/SiO 2 substrate obtained using combined FUV exposure and thermal annealing at (a) 200 C + FUV for 30 min, (b) 150 C + FUV for 180 min, (c) 150 C + FUV for 90 min, and (d) 150 C + FUV for 30 min. S-9

10 Figure S8. (a) Capacitance-frequency plot, and (b) capacitance-bias voltage plot for Al/Al 2 O 3 (50 nm)/al capacitors on PEN substrate where the Al 2 O 3 was grown with atomic layer deposition (ALD) at 150 C. References (1) Welge, K. H.; Stuhl, F. Energy Distribution in the Photodissociation H2O H(12S) +OH(X 2II). J. Chem. Phys. 1967, 46 (6), (2) Goldstein, S.; Rabani, J. Mechanism of Nitrite Formation by Nitrate Photolysis in Aqueous Solutions: Role of Peroxynitrite, Nitrogen Dioxide, and Hydroxyl Radical. J. Am. Chem. Soc. 2007, 129 (34), (3) SenGupta, S.; Upadhyaya, H. P.; Kumar, A.; Naik, P. D. OH Formation Dynamics in 193nm Photolysis of 2-Methoxyethanol: A Laser Induced Fluorescence Study. Chem. Phys. 2014, 443, (4) Derby, B. Inkjet Printing of Functional and Structural Materials: Fluid Property Requirements, Feature Stability, and Resolution. Annu. Rev. Mater. Res. 2010, 40 (1), (5) Tiilikainen, J.; Tilli, J.-M.; Bosund, V.; Mattila, M.; Hakkarainen, T.; Airaksinen, V.-M.; Lipsanen, H. Nonlinear Fitness space structure Adaptation and Principal Component Analysis in Genetic Algorithms: An Application to X-Ray Reflectivity Analysis. J. Phys. D Appl. Phys. 2007, 40 (1), (6) Fairley, K. C.; Merrill, D. R.; Woods, K. N.; Ditto, J.; Xu, C.; Oleksak, R. P.; Gustafsson, T.; Johnson, D. W.; Garfunkel, E. L.; Herman, G. S.; Johnson, D. C.; Page, C. J. Non- Uniform Composition Profiles in Inorganic Thin Films from Aqueous Solutions. ACS Appl. Mater. Interfaces 2016, 8 (1), S-10