Study of P(VDF-co-HFP)-ionic liquid based ionogels for designing flexible displays

In flexible displays, solid electrolytes promote electron-transfer without compromising system integrity. Ionogels (IGs) are now preferred among other solid electrolytes, e.g. inorganic and hydrogel electrolytes, for being easier to produce than the former and showing excellent properties, including high ionic conductivities, broad electrochemical window, transparency, flexibility, and non-solvent volatility than the latter. IG properties widely depend on the composition and concentration of the ionic liquid (IL) in the polymeric matrix, affecting its transparency, integrity and flexibility. Here, we have investigated the loading and composition of the IL to produce P(VDF-co-HFP)-based IGs to be employed as substrates in the development of flexible photo-electrochromic displays. Single IG layers of P(VDF-co-HFP) loaded with 79% wt. of N₁₁₁₄ TFSI were optimal among the IGs formulations, reaching conductivity values up to 1.06 mS·cm⁻¹, showing high transparency (83% transmittance) and a large electrochemical window (3.2 V), while maintaining flexibility and integrity. The doping of the IG with the photo-electrochromic molecule spiropyran resulted in flexible displays with fast and reversible electrochromic and photochromic dynamics, not affecting the conformational changes of the molecule. These flexible photo-electrochromic displays, due to its simplicity, high-performance and low cost, are foreseen to impact in several fields, including smart windows, smart clothing or gas sensors, among others.