Title Page
Contents
ABSTRACT 12
Introduction 16
Chapter Ⅰ. Theoretical background 19
1. P3HT 19
2. Metal-Doping 21
3. Self-seeded growth with crystal seed 22
Chapter Ⅱ. Experimental methods 24
1. Materials 24
2. Fabrication of Ag NW/Ecoflex Electrode 24
3. Fabrication of Li-P3HT/SBS arrays 27
4. Characterization of strain sensor 27
5. Finite Element Analysis of sensing layer on Ag NW/Ecoflex electrode 28
Chapter Ⅲ. Results and discussion 29
1. Characterization of Li-P3HT/SBS film 29
1.1. Complexation of Li-Thiophene backbones 29
1.2. Improvement of crystallinity 33
1.3. Electronic structure 39
1.4. Percolation theory 43
1.5. Effect of difference in molecular weight of P3HT 46
1.6. Investigation for other dopants 48
2. Improvement in mechanical properties 53
2.1. Stress-Strain curve 53
2.2. Finite element analysis 56
2.3. Viscosity 59
2.4. Gauge Factor 61
2.5. Cycling performances 63
2.6. Stability tests 63
3. Applications 67
3.1. Gesture monitoring 67
3.2. Pulse sensor 67
Chapter Ⅳ. Conclusion 70
Chapter Ⅴ. Reference 71
ABSTRACT IN KOREAN 82
Figure 2.1. The stacking structure of P3HT nanofibrils. The hole mobility is highest along the Thiophene backbone (P3HT) and lower in the 𝜋-𝜋 stacking direction. 20
Figure 2.2. (A) Scheme of the transition of P3HT from the dissolved polymer to the nanorods and to the nanofibrils as the temperature of the solubility decreased. The... 23
Figure 3.1. (A) Schematic illustrating the overall fabrication process of Ag nanowire/Ecoflex flexible electrodes (B) SEM image for the surface of the free-... 26
Figure 4.1. (A) Schematic illustrating the doping process of P3HT backbones with Li-TFSI. (B) Schematic showing the growth of Li- P3HT nanofibrils along to the... 31
Figure 4.2. (A) Photograph of Li-P3HT/SBS solution after dissolved at 70 ℃ for 5 min (left) and cooled solution (right) (B) Photograph of the P3HT/SBS solutions for... 32
Figure 4.3. A-C) AFM topographic images of the pristine P3HT, Li-P3HT, and Li- P3HT/SBS thin films, respectively. The ratio of Li-TFSI was fixed at 4.5 μM. (D)... 35
Figure 4.4. (A) AFM phase image of Li-P3HT/SBS film. (B) Height profile of the Li-P3HT/SBS film on Si wafer. All samples in AFM images were prepared for... 36
Figure 4.5. AFM image of the Li-P3HT/SBS thin film (Li-TFSI=6.0 μM). The precipitate is separated Li-TFSI. 37
Figure 4.6. UV-Vis spectra of Li-P3HT/SBS thin films coated onto a slide glass for α=0.67 and ratio of Li-TFSI=0 - 6.0 μM. 38
Figure 4.7. (A and B) UPS spectra of Li-P3HT/SBS thin films (α=0.67, concentration of Li-TFSI=0-6.0μM) measured at high-and low-binding energy... 41
Figure 4.8. Electrical resistance-channel length plots of the pristine P3HT/SBS and Li-P3HT/SBS active layers (α=0.67, concentration of Li-TFSI=4.5 μM) obtained... 42
Figure 4.9. Fitting curve of the theoretical conductivities of Li-P3HT/SBS thin film (α=0.4, Li-TFSI=4.5 μM) calculated according to the percolation theory 45
Figure 4.10. (A) AFM topographic image of Li-P3HT/SBS (molecular weight of P3HT=20 kDa). (B) Experimentally calculated conductivities of Li-P3HT/SBS... 47
Figure 4.11. Images of the Fe-doped P3HT/SBS solution. (Left) As doped solution. (Right) After mixing with vortex mixer 49
Figure 4.12. (A and B) UPS spectra of Ag-P3HT/SBS thin films (α=0.67, AgCF₃COO=0 - 8 mM) measured at high and low binding energy regime,... 50
Figure 4.13. (A and B) Hole concentrations and conductivities of Ag-P3HT/SBS, respectively. 51
Figure 4.14. TEM image of Ag-P3HT/SBS stored at room temperature for 24h. 52
Figure 4.15. (A-C) OM images of the Li-P3HT/SBS sensing layers (α=0.67, Li- TFSI=4.5 μM) at strains of 0%, 30%, and 50%. (D and E) OM images of the Li-... 55
Figure 4.16. Maximum strain distributions on (A) pure P3HT array and (B-D) Li- P3HT/SBS arrays (α=1.0, 0.67, and 0.4). von Mises stress distributions on (E) pure... 57
Figure 4.17. Probability distributions of Li-P3HT/SBS arrays for (A-D) maximum strain (pure P3HT, α=1.0, 0.67, and 0.4) and (E-H) von Mises stress (pure P3HT, α... 58
Figure 4.18. (A) Shear viscosity-temperature curve of the Li-P3HT/SBS solution. The shear viscosity was measured at a shear rate of 60 s⁻¹. (B)OM images of the Li-... 60
Figure 4.19. Gauge factors (GFs) of the strain sensors (α=0.67, Li-TFSI=1.5 and 3.0 μM) at strains of 0 - 50% 62
Figure 4.20. Sensitivity of the strain sensors according to the applied strains (0 - 50%). 64
Figure 4.21. Relative conductivities of the Li-P3HT/SBS active layer (α=0.67, Li- TFSI=4.5 μM) for the stretching cycles (0 - 1000). 65
Figure 4.22. Relative conductivities of the Li-P3HT/SBS active layer measured in air at 25℃ and 25% relative humidity for 800 h. The device was not encapsulated. 66
Figure 4.23. Photographs of the strain sensor-attached artificial finger for the different bending angles (0°, 30°, 60°, and 90°) 68
Figure 4.24. Applications of the Li-P3HT/SBS nanocomposites (α=0.67, Li-TFSI=4.5 μM). (A) Gauge factors of the strain sensor at strains of 0 - 50%. (B) Resistance... 69