Thermally Stable Colorless Copolyimides with a Low Dielectric Constant and Dissipation Factor and Their Organic Field-Effect Transistor Applications

Abstract

We developed highly thermally resistant and colorless polyimides (CPIs) with an ultralow coefficient of thermal expansion (CTE) and sufficient mechanical durability as a flexible substrate for organic field-effect transistors (OFETs). The CPIs were synthesized from trans-1,4-cyclohexyl diamine (t-CHDA) with different ratios of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and pyromellitic dianhydride (PMDA). The effects of the composition of s-BPDA and PMDA on the thermal, mechanical, electrical, and optical properties of CPIs were investigated. The optimized CPI, PI-3 with 90 mol % s-BPDA and 10 mol % PMDA, showed a relatively high elongation at break (8%) with a low CTE of 14 ppm K–1, a high glass transition temperature (T g) of 340 °C, and a large tensile modulus (E) of 4.1 GPa, respectively. Besides, PI-3 possessed a high transparency with a light transmittance at 400 nm (T 400) of 81% and a low cutoff wavelength (λcutoff) of 349 nm. Next, the dimer diamine of DDA (Priamine 1074) was introduced into the PI-3 structure to reduce the dielectric constant and enhance the stretchability. For example, PI-6C, with 85 mol % t-CHDA and 15 mol % DDA, showed a low dielectric constant (D k) of 2.8, a low dissipation factor (D f) of 0.004, and a high T 400 of 86% with maintained thermal and mechanical properties. Finally, a flexible OFET device using PI-3 as the substrate and dielectric was fabricated and characterized and exhibited an outstanding performance preservation after 1000 bending cycles or the high-temperature heating test, suggesting its excellent durability. The experimental results indicate that the CPIs studied have potential applications for transparent organic electronic devices.

Enhancement of Ultraviolet Light Resistance of Colorless and Transparent Semi-Alicyclic Polyimide Nanocomposite Films via the Incorporation of Hindered Amine Light Stabilizers for Potential Applications in Flexible Optoelectronics

“…The composite solutions were first prepared by blending the CPI-0/DMAc solution and the HALS/DMAc solution with the total 1 Full-width at half-maximum. 2 T 5% , T 10% : 5% and 10% weight loss temperature, respectively; T max : the temperature at the maximum decomposition speed; R w500 : residual weight ratio at 500 • C in nitrogen. 3 Not applicable.…”

“…Colorless and transparent polyimide (CPI) films have been well known for the excellent combined thermal and optical properties for many years in advanced optical and optoelectronic applications [ 1 , 2 , 3 ]. In many practical applications, CPI films have to be 1qconfronted with the long-term ultraviolet-visible (UV) light exposure, such as the fluorinated CPI thermal control films for the space aircrafts have to endure the large doses of ultraviolet (UV) and vacuum ultraviolet (VUV) irradiation during the servicing life, and the CPI substrates for flexible photovoltaic solar cells will be irradiated by sunlight in the whole life.…”

“…Optical properties of CPI/HALS nanocomposite films. Cutoff wavelength 2. T 400 , T 450 : Transmittance at 400 nm and 450 nm at a thickness of 25 µm, respectively.…”

Charge recombination suppression in dye-sensitized solar cells by tuning the dielectric constant of triphenylamine dyes with altering π-bridges from naphthalene to anthracene units

“…Moreover, the tangent loss (tan d) of the capacitors was detected using a portable digital LCRmeter (ESCORT ELC-133A model, Taiwan) by setting the instrument at 1.0 V and an alternative ac current voltage across Al electrodes of the capacitors. For this, we used eqn ( 4)-( 6) as follows: [32][33][34][35][36][37][38]…”

“…Moreover, the tangent loss (tan δ ) of the capacitors was detected using a portable digital LCRmeter (ESCORT ELC-133A model, Taiwan) by setting the instrument at 1.0 V and an alternative ac current voltage across Al electrodes of the capacitors. For this, we used eqn (4)–(6) as follows: 32–38 σ ac = 2π fε 0 ε ′tan δ where C , d , A , f , ε ′, ε ′′, ε 0 , σ ac , and δ represent the capacitance (F), thickness (m), area of electrodes (m 2 ), applied frequency ( f , Hz), dielectric constant of dyes, imaginary dielectric constant, permittivity of the free space (8.854 × 10 −12 F m −1 ), ac conductivity (Ω −1 m −1 ), and loss factor of the capacitors, respectively.…”