Supplementary information Improving the Working Efficiency of a Triboelectric Nanogenerator by the Semimetallic PEDOT:PSS Hole Transport Layer and its Application in Self- Powered Active Acetylene Gas Sensing A.S.M. Iftekhar Uddin, Usman Yaqoob, Gwiy-Sang Chung* School of Electrical Engineering, University of Ulsan, 93 Daehak-ro, Nam-gu, Ulsan 44610, Republic of Korea * Corresponding author. E-mail address: gschung@ulsan.ac.kr (G.-S. Chung) S-1
Figure S1. FESEM images of the (a) as-fabricated porous Si mold and (b) sputtered ZnO thin film on Si substrate. To synthesis the porous silicon (p-si) mold, silver nanoparticles (Ag NPs) were deposited on a 4 4 cm 2 nativeoxide etched p-type Si (100) wafer using RF magnetron sputtering for 12 sec (Ag NP size ~ 40-60 nm). After metallization, the wafer was etched for 15 min using the HF + H 2 O 2 + H 2 O etchant solution; then rinsed into HNO 3 solution for 5 min to remove the Ag NPs. After cleaning with acetone, isopropanol, and de-ionized water the mold was functionalized using a piranha solution (H 2 SO 4 + H 2 O 2 ) to crosslink a thin epoxy layer on the porous surface. Subsequently, the p-si master was treated with trimethylchlorosilane (TMCS, Sigma Aldrich) by vacuum phase silanization to avoid adhesion between the PDMS and p-si mold. S-2
Figure S2. Experimental setup: (a) schematic illustration and (b) photograph. (a, inset) Photograph of the as-fabricated TENS device; this device is placed in the indicated region of (a) for testing. The gas chamber apparatus is omitted from the schematic for clarity. S-3
Figure S3. I-V characteristics of the bare PEDOT:PSS and the EG-functionalized PEDOT:PSS films (a) in dark and (b) under 110 mw cm -2 light illumination. S-4
Figure S4. Output voltage of TENG devices versus EG concentration in the EG-functionalized PEDOT:PSS film, in both indoor and outdoor (i.e., under sunlight) conditions. S-5
Figure S5. Surface charge distribution at the (a) PDMS-ITO and (b) PDMS-EPP-ITO interfaces in dark (a-i and b-i) and under 110 mw cm -2 light irradiation (a-ii and b-ii). Color legend represents the charge distribution on the surface. (c) Surface charge density of the TENG without and with EPP layer in dark and at different light intensities. S-6
Figure S6. Output voltage variations of the TENG (indoors), under various (a) pressing (contact) forces and (b) external pressing frequencies. S-7
Figure S7. Output voltage profiles of the TENG (indoors), when configured with (a) forward and (b) reverse connections. S-8
Figure S8. Electrical characteristics of the TENG under the peak contact force of 3.2 N and external pressing frequency of 0.5 Hz: (a, c) output voltage and (b, d) current density; (a, b) indoors, (c, d) outdoors. S-9
Figure S9. Schematic illustration of the C 2 H 2 sensing mechanism of Ag@ZnO film in the TENS (a) in dark and (b) under light illumination. S-10
Figure S10. Surface charge distribution at the Ag@ZnO-nylon interface (a) in dark and (b-e) at different light intensities. (b) 25 mw cm -2, (c) 60 mw cm -2, (d) 85 mw cm -2, and (e) 110 mw cm -2. Color legend represents the charge distribution on the surface. S-11
Figure S11. Contact angle measurement of the (a) flat and (b) wrinkle patterned PDMS film. Contact angle measurements of the flat PDMS and wrinkled patterned PDMS are shown in Figure S10a and S10b, which determine the surface properties of the as-fabricated w-pdms film. The contact angle of the flat PDMS and wrinkled-pdms are nearly 102.2 o and 127.9 o, respectively. The surface energy of the wrinkled- PDMS is nearly 0.0076 mn/m, which is much lower than the flat PDMS film (~2.58 mn/m). This phenomenon indicates the higher surface roughness of the wrinkled-pdms in comparison to the flat PDMS film. S-12
Table S1. A comparison of the C 2 H 2 sensing performance of the TENS to that of previous reported works. Sensor type Materials Response, S (Detection range (ppm)) External power requirement Operating temperature Ref. Ni/ZnO 17 a to 2000 ppm (100-2000 ppm) Yes 250 o C [S1] Pt/ZnO 43 a to 1000 ppm (50-10000 ppm) Yes 300 o C [S2] ZnO 52 a to 200 ppm (1-4000 ppm) Yes 420 o C [S3] ZnO/RGO 18.2 a to 100 ppm (30-1000 ppm) Yes 250 o C [S4] Ag/ZnO 92% b to 1000 ppm (5-1000 ppm) Yes 200 o C [S5] Ag/ZnO-RGO 21.2 a to 100 ppm (1-1000 ppm) Yes 150 o C [S6] (flexible) Ag/ZnO 27.2 a to 1000 ppm Yes 200 o C [S7] Au/ZnO NiO/SnO 2 Triboelectric Ag/ZnO 19.4% b to 500 ppm (dark) 46.9% b to 500 ppm (light) (25-500 ppm) 13.8 a to 100 ppm (1-1000 ppm) 39.2% c to 100 ppm (indoor) 46.5% c to 100 ppm (outdoor) (30-1000 ppm) Yes 25 o C [S8] Yes 206 o C [S9] No 25 o C This study a R a/r g b (R a-r g)/r a 100 c (V a-v g)/v a 100 References (S1) Wang, X.; Zhao, M.; Liu, F.; Jia, J.; Li, X.; Cao, L. C 2 H 2 Gas Sensor Based on Ni-Doped ZnO Electrospun Nanofibers. Ceram. Int. 2013, 39, 2883-2887. (S2) Tamaekong, N.; Liewhiran, C.; Wisitsoraat, A.; Phanichphant, S. Acetylene Sensor based on Pt/ZnO Thick Films as Prepared by Flame Spray Pyrolysis. Sens. Actuators B 2011, 152, 155-161. (S3) Zhang, L.; Zhao, J.; Zheng, J.; Li, L.; Zhu, Z. Hydrothermal Synthesis of Hierarchical Nanoparticle- Decorated ZnO Microdisks and the Structure-Enhanced Acetylene Sensing Properties at High Temperatures. Sens. Actuators B 2011, 158, 144-150. (S4) Uddin, A. S. M. I.; Chung, G. -S. Synthesis of Highly Dispersed ZnO Nanoparticles on Graphene Surface and Their Acetylene Sensing Properties. Sens. Actuators B 2014, 205, 338-344. S-13
(S5) Lee, K. -W.; Uddin, A. S. M. I.; Phan, D. -T.; Chung, G. -S. Fabrication of Low Temperature Acetylene Gas Sensor based on Ag Nanoparticles-Loaded Hierarchical ZnO Nanostructures. Electron. Lett. 2015, 51, 572-574. (S6) Uddin, A. S. M. I.; Phan, D. -T.; Chung, G. -S. Low Temperature Acetylene Gas Sensor based on Ag Nanoparticles-Loaded ZnO-Reduced Graphene Oxide Hybrid. Sens. Actuators B 2015, 207, 362-369. (S7) Uddin, A. S. M. I.; Yaqoob, Y.; Phan, D. T.; Chung, G. -S. A Novel Flexible Acetylene Gas Sensor based on PI/PTFE-Supported Ag-Loaded Vertical ZnO Nanorods Array. Sens. Actuators B 2016, 222, 536-543. (S8) Zheng, Z. Q.; Wang, B.; Yao, J. D.; Yang, G. W. Light-Controlled C 2 H 2 Gas Sensing based on Au ZnO Nanowires with Plasmon-Enhanced Sensitivity at Room Temperature. J. Mater. Chem. C 2015, 3, 7067-7074. (S9) Lin, Y.; Li, C.; Wei, W.; Li, Y.; Wen, S.; Sun, D.; Chen, Y.; Ruan, S. A New Type of Acetylene Gas Sensor Based on a Hollow Heterostructure. RSC Adv. 2015, 5, 61521-61527. S-14