Evaluation of encapsulation strategies for solution-processed flexible organic light-emitting diodes

Abstract

Owing to the sensitivity of organic materials to ambient conditions, encapsulation of organic light-emitting diodes (OLEDs) is critical. In this work, Al2O3 film, deposited by atomic layer deposition (ALD) technique, on flexible polyethylene terephthalate (PET) substrate is used as a barrier film. Al2O3 is also deposited directly on OLED as thin-film encapsulation. Electrical Ca tests are used to measure water vapor transfer rate (WVTR) values, and an optimum WVTR value of 9 *10−4 g/m2/day using 43 nm Al2O3 film has been obtained. The related results on five different encapsulation structures for solution-processed OLEDs: (i) glass to glass encapsulation (G2G) as a reference, (ii) glass to barrier film encapsulation (G2B), (iii) glass to direct thin-film encapsulation (G2D), (iv) barrier to barrier film encapsulation (B2B), and (v) barrier to direct thin-film encapsulation (B2D), are evaluated. The operating half-lifetime values of OLEDs with G2B- and G2D-encapsulation are 54% and 82% of the half-lifetime with G2G encapsulation, respectively. The lifetime of flexible OLED devices with B2D encapsulation is also 34% more than that with B2B encapsulation. Based on the bending stress analysis, the estimated critical bending radius for B2B and B2D encapsulation of flexible OLEDs are 16.83 and 7.07 mm, respectively.