**4. Conclusion**

In this study, we successfully synthesized a series of hybrid dielectric films using polyimide and SiO2-TiO<sup>2</sup> nanoparticles without polymer additives, namely polyimide-TiO2-SiO2, polyimide-TiO2-SiO2:D2000, and polyimide-TiO2-SiO2:PU. Pffbt4t-2OD was used in the semiconductor layer. The addition of Jeffamine D2000 (D2000) and polyurethane (PU) as additives was observed to increase the tensile properties without affecting the original electrical properties. The results suggest that the C30-based OTFT achieves the best tensile effect of 50% train after 150 cycles subject to the 10% mobility reduction because the polyurethane polymers are softer and can provide a denser and more concentrated film structure, which facilitates the stretching of the device. Through the adjustment of the ratios of various TiO2-SiO<sup>2</sup> inorganic nanoparticles, the dielectric constant of the hybrid material can be adjusted, thereby significantly improving the dielectric properties of the dielectric layer. The device properties (mobility and threshold voltage) and film properties (dielectric constant, surface morphology, and hydrophilic hydrophobicity) exhibit a strong correlation to the proportion of TiO2-SiO<sup>2</sup> inorganic nanoparticles. This study shows that the prepared hybrid films can be customized according to the requirements for practical applications. In addition, our PI-hybrid material has the advantage of transparency, high thermal stability, and environmental safety. The addition of Jeffamine D2000 and polyurethane can increase tensile properties without affecting the original electrical properties and widen the applicability of OTFT devices.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4360/12/5/1058/s1, Figure S1: The TEM image of inorganic TiO<sup>2</sup> -SiO<sup>2</sup> nanoparticles; Figure S2: The optical transmittance of A0, A30, B30, and C30 films as the dielectric layer of OTFTs device; Figure S3: The transfer curves of OTFTs prepared by different dielectric layer materials, A0, A30, B30, and C30; Figure S4: The output characteristics of the OTFTs prepared by different dielectric layer materials: (a) A0, (b) A30, (c) B30, and (d) C30.

**Author Contributions:** Conceptualization, Y.-Y.Y.; Data curation, C.-H.Y.; Funding acquisition, Y.-Y.Y.; Investigation, Y.-Y.Y. and C.-H.Y.; Methodology, C.-H.Y.; Project administration, Y.-Y.Y.; Supervision, Y.-Y.Y.; Writing—original draft, Y.-Y.Y.; Writing—review & editing, Y.-Y.Y. All authors have read and agreed to the published version of the manuscript.

**Acknowledgments:** We thank the Ministry of Science and Technology of Taiwan (MOST 108-2221-E-131-003) for providing financial support.

**Conflicts of Interest:** The authors declare no conflict of interest.
