Colorless polyimides (CPIs) have encountered new challenges for higher optical performance including transmittance (T% > 90%) in visible range and yellow index (YI < 2.0), to be utilized as substrates of cover window or touch panel in the foldable displays. With persistent efforts, the highest transmittance of conventional CPIs has barely reached about 88%, while still cannot satisfy the optical requirement. In this work, soluble sulfoxide biphenyl polyimide PI (TFSODA/BPDA) with high optical performance (T% = 88.5%, YI = 3.2) was successfully fabricated by a low-temperature (about 220 °C) process rather than high-temperature process (over 300 °C). Then, a finely designed inorganic anti-reflection coating was pioneering utilized on the sulfoxide polyimide film to further improve its transparency. The combination of chemical modification of molecular structure and physical regulation of incident light energy on the surfaces leads to a transmittance of 91% in the visible range, a YI of 2.9, and an effective enhancement of surface performance. In addition, the resultant sulfoxide biphenyl polyimide also exhibited excellent thermal durability (T_g = 327 °C) and dimension stability (CTE = 24.7 ppm/K in the range of 50–300 °C), which was attractive for applications in foldable displays.

无色聚酰亚胺 (CPI) 面临着更高光学性能的新挑战，包括在可见光范围内的透射率 (T% > 90%) 和黄色指数 (YI < 2.0)，可用作可折叠显示器中的盖窗或触控面板的基板。经过不懈努力，传统CPI的最高透光率勉强达到88%左右，仍不能满足光学要求。在这项工作中，通过低温（约220°C）工艺而不是高温工艺成功制备了具有高光学性能（T% = 88.5%，YI = 3.2）的可溶性亚砜联苯聚酰亚胺PI（TFSODA/BPDA） （超过 300 °C）。然后，在亚砜聚酰亚胺薄膜上率先使用了精心设计的无机减反射涂层，以进一步提高其透明度。分子结构的化学修饰和表面入射光能量的物理调节相结合，使可见光范围内的透射率为91%，YI为2.9，有效提高了表面性能。此外，所得亚砜联苯聚酰亚胺还表现出优异的耐热性（T _g  = 327 °C）和尺寸稳定性（CTE = 24.7 ppm/K，在 50–300 °C 范围内），这对于可折叠显示器的应用很有吸引力。