Light Out-Coupling for OLED Devices
The display sector is synchronously concerned with improving the functionalities of devices while reducing their size and weight profiles. Since liquid crystal display (LCD) technologies outstripped the functional and production capabilities of cathode ray tube (CRT) technology, the display markets have been focussed on engineering increasingly thin and lightweight displays for domestic use. Printed electronics have supported this innovative trajectory, providing specialty materials and novel deposition methods for producing high functionality organic light emitting diode (OLED) devices.
OLEDs generate light via the recombination process where excited electrons transition through an organic semiconductor sandwiched between an anode and a cathode. These electrons lose energy as they fall out of the conduction band by emitting photons of light. When electrically-charged between the anode and the cathode, the organic semiconductor spontaneously emits light in any direction. It can propagate both internally and externally.
Total internal reflection refers to the amount of light that propagates inwards and is lost, causing low levels of light to reach the screens of OLED devices. Up to 80% of the light generated in an OLED device can be lost due to internal reflection.
This blog post will explore the development of a specialty technique known as light out-coupling for improving the development of OLED devices.
Explaining Light Out-Coupling for OLED Devices
Light out-coupling techniques through nanoparticle printing can provide superior efficiency levels for and improve the direction of light propagation within OLED devices. These methods include nanocontact printing and nanoimprinting.
Installing two-dimensional nanopatterned photonic crystal structures in glass substrates has proven successful in enhancing light out-coupling in OLED devices and providing various control of photon propagation. This method can provide an enhancement factor of 1.5 across a viewing angle of ±40°, through periodic modulation of internally reflected waves of light. This supports the conversion of guided waves in the high refractive-index layers into externally directed waves of light.
High functionality optical coatings for light out-coupling can radically improve light extraction in OLED devices. Coating materials with high refractive-indices of up to 1.85 can be used to planarize micropatterns or minimize the refractive indices at interfaces and improve the propagation of photons out through the glass substrate screen of the device. Certain specialty materials can be incrementally adjusted up to the highest refractive-index of 1.95 if necessary.
Light Out-Coupling with Avantama
With significant experience in the fields of nanotechnology and printed electronics, Avantama is uniquely placed to support improvements for OLED devices at every stage of development. Our materials are engineered to improve the manufacturing processes and enhance the end-product functionalities of thin film electronics.
If you would like more information about developing light out-coupling optical coatings with Avantama, please do not hesitate to contact us.