Adjustable white-light emission from a photo-structured micro-OLED array

White organic light-emitting diodes(OLEDs)are promising candidates for future solid-state lighting applications and backplane illumination in large-area displays.One very specific feature of OLEDs,which is currently gaining momentum,is that they can enable tunable white light emission.This feature is conventionally realized either through the vertical stacking of independent OLEDs emitting different colors or in lateral arrangement of OLEDs.The vertical design is optically difficult to optimize and often results in efficiency compromises between the units.In contrast,the lateral concept introduces severe area losses to dark regions between the subunits,which requires a significantly larger overall device area to achieve equal brightness.Here we demonstrate a color-tunable,two-color OLED device realized by side-by-side alignment of yellow and blue p-i-n OLEDs structured down to 20μm by a simple and up-scalable orthogonal photolithography technique.This layout eliminates the problems of conventional lateral approaches by utilizing all area for light emission.The corresponding emission of the photo-patterned two-unit OLED can be tuned over a wide range from yellow to white to blue colors.The independent control of the different units allows the desired overall spectrum to be set at any given brightness level.Operated as a white light source,the microstructured OLED reaches a luminous efficacy of 13 lm W^(−1) at 1000 cd m^(−2) without an additional light outcoupling enhancement and reaches a color rendering index of 68 when operated near the color point E.Finally,we demonstrate an improved device lifetime by means of size variation of the subunits.

Real-time beam shaping without additional optical elements

Providing artificial light and enhancing the quality of the respective light sources is of continued interest in the fields of solid state,condensed matter,and semiconductor physics.Much research has been carried out to increase the luminous efficiency,lifetime and colour stability of such devices.However,the emission characteristics of a given light source do not necessarily comply with today’s often sophisticated applications.Here,beam shaping addresses the transformation of a given light distribution into a customized form.This is typically achieved by secondary optical elements often sporting elaborate designs,where the actual light source takes up only a small fraction of the system’s volume.Such designs limit the final light source to a single permanent operation mode,which can only be overcome by employing mechanically adjustable optical elements.Here we show that organic light-emitting diodes(OLEDs)can enable real-time regulation of a beam shape without relying on secondary optical elements and without using any mechanical adjustment.For a red light-emitting two-unit OLED architecture,we demonstrate the ability to continuously tune between strongly forward and strongly sideward emission,where the device efficiency is maintained at an application-relevant level ranging between 6 and 8%of external quantum efficiency for any chosen setting.In combination with additional optical elements,customizable and tuneable systems are possible,whereby the tuning stems from the light source itself rather than from the use of secondary optics.