Broadband Light Out‐Coupling Enhancement of Flexible Organic Light‐Emitting Diodes Using Biomimetic Quasirandom Nanostructures

Abstract

Flexible organic light-emitting diodes are gaining increasing importance as a leading technology for high-quality displays and lighting in wearable electronics due to their low power consumption, excellent color gamut, and the desirable mechanical fl exibility with soft materials and curvilinear surfaces. However, further enhancements in effi ciency are still challenging because of the optical confi nement and limited light out-coupling effi ciency. Here, a simple and wavelength-independent light extraction scheme is demonstrated using the biomimetic quasirandom nanostructures that can simultaneously enhance the out-coupling of the waveguided light and allow the minimized ohmic losses without spectral distortion. Compared to periodic grating structures, the nanoimprinted quasirandom nanostructures can broaden the periodicity and randomize the emission directionality, leading to the superiority of color stability over the visible wavelength range for a large variation of viewing angles. The resulting external quantum effi ciency and current effi ciency are 1.51 and 1.43 times that of a conventional fl exible organic lightemitting diode used as a comparison, respectively.

Wetting characteristics of 3-dimensional nanostructured fractal surfaces

“…Similar structures have been used to decrease the drag on a surface, manipulate droplets, control adsorption of biomolecules, and promote cell adhesion [37][38][39][40]. Recently, flexible organic lightemitting diodes were fabricated with a nanoimprinting process to increase the efficiency for wearable electronics [41]. Similar structures to those discussed above could be fabricated to act as a mold for this nanoimprinting procedure and help increase the efficiency of components in the rapidly growing field of electronics integration.…”

Enhanced light extraction efficiency and viewing angle characteristics of microcavity OLEDs by using a diffusion layer

“…Additionally, Devices A and B (MC-OLEDs with the additional diffusion layer) do not exhibit a perfectly flat surface despite the insertion of the ZnO semiplanarization layer. A corrugated OLED reportedly has a higher current density than a planar OLED 32 . This phenomenon is also apparent in our work.…”

Thin-film organic semiconductor devices: from flexibility to ultraflexibility

“…To further enhance the light extraction or light trapping in the devices, nanostructures or nanoparticles are introduced into these TFC electrodes for improving the device performances [47,[130][131][132][133][134][135][136][137][138][139][140]. Besides these thin-film electrodes, fiber-/mesh-shaped electrodes also demonstrated good flexibility [17,51,64,67,68].…”

“…The reported electrodes utilized in flexible OLEDs are mainly based on PEDOT [173], CNT [44,174], Ag NWs/grids [175][176][177][178][179], graphene [45,180], ITO [76], and metal oxide [181]. For achieving higher efficiency, top-emitting architectures [182][183][184][185] and nanostructured/scattered electrodes or substrates [47,[130][131][132][133][134][135] can be adopted, to enhance output coupling or light extraction of the devices. However, to achieve high flexibility, extremely bendable TFC electrodes firstly need to be developed [88,120,124,146,147,177,186].…”