Fabrication of wrinkle-patterned polydimethylsiloxane films as light out-coupling structure for white OLEDs

Light out-coupling is an important strategy for the performance enhancement of white organic light-emitting diodes (OLEDs). Polydimethylsiloxane (PDMS), as a famous transparent elastomer, has the potential of using as a light extraction structure for OLED devices. Here, wrinkle-patterned PDMS films were in-situ fabricated via breath figure method together with spin coating process in a highly humid environment onto the glass side of the ITO substrate. The effect of solvent additive on the wrinkle morphology were investigated. The PDMS films were introduced into two different white OLED devices to extract the light of the substrate mode at the substrate-air interface. The maximum luminance improves 30.7% and 50.4%, respectively. While OLEDs also show appreciable enhancement with 31% and 11% in external quantum efficiencies due to luminance increase. Additionally, finite-difference time-domain (FDTD) simulations were performed to get insight into the mechanism of the light extraction enhancement due to the PDMS wrinkle structure. The reduced total internal reflections at the substrate-glass interface seems to increase the light out-coupling. We infer from these results that wrinkle-patterned PDMS films help to extract more light confined to the interior of white OLEDs, thereby improving the device performance. This work provides a relatively simple method to efficiently extract light from white OLEDs.