**4.1 Challenges of CPI for TaFEs**

Targeting the applications of transparent and flexible electronics, it is of priority that CPI film owns satisfied optical, mechanical, thermal, chemical, optical, and electrical properties. For the key applications, the specifications of such properties are listed in **Table 1**. Like other materials, usually, the physical and chemical properties of CPI film are not independent; it is always the case that we need to adjust the composition and structure of the CPI film to balance the needs of the properties. However, there are major challenges we have to take, with the consideration of balancing the overall performance of the CPI film (**Table 7**).
