Flexible encapsulation materials based on silica aerogels for organic light-emitting diodes

In this study, we present flexible encapsulation materials using silica aerogels for organic light-emitting diodes (OLEDs). The encapsulation consists of three layers: a superhydrophobic film of silica aerogels and polydimethylsiloxane (PDMS), an organic interlayer of polystyrene (PS), and a dense oxide layer of ZnO. The superhydrophobic film limits the contact with moisture, and the water vapor transmission rate (WVTR) can be further reduced by inserting a PS-covered ZnO layer between the substrate and the silica aerogel/PDMS composite layer. The PS interlayer was used to block the pathway for moisture diffusion through pinholes in ZnO. Trimethylchlorosilane (TMCS) was added to the superhydrophobic film as the silylation agent to remove the residual hydroxyl group on the surface of the aerogel. The chemical modification of aerogel surfaces was confirmed using Fourier transform infrared spectroscopy (FTIR). The superhydrophobicity, WVTR, and pore size of encapsulation materials were analyzed via the contact angle, MOCON test, and BET, respectively. The mechanical flexibility of the encapsulation was evaluated using the cyclic bending test and contact angle measurement. After 2000 bending cycles at a 10 mm bending radius, the contact angle was maintained at 180°. OLEDs were fabricated with and without the encapsulation, and the lifetime was measured and compared. For the encapsulation with a WVTR of 0.022 g/m². day, the OLED showed a consistent performance for 7 hours, which is comparable to that of an OLED with the conventional glass lid encapsulation.