Printing of Large‐Scale, Flexible, Long‐Term Stable Dielectric Mirrors with Suppressed Side Interferences

Abstract

Dielectric mirrors are wavelength‐selective mirrors which are based on thin film interference effects. Their optical band can precisely be adjusted in width, position, and reflectance by the refractive index of the applied materials, the layers' thicknesses, and the amount of deposited layers. Nowadays, they are a well‐known light management tool for efficiency enhancement in, for example, semitransparent organic solar cells (OSCs) and light guiding in organic light‐emitting diodes (OLEDs). However, most of the dielectric mirrors are still fabricated by lab‐scale techniques such as spin‐coating or physical vapor deposition under vacuum. Large‐scale, fully printed (maximum 20 × 20 cm2) dielectric mirrors with adjustable reflectance characteristics are fabricated, using temperatures of maximum 50 °C and alcohol‐based inks. According to the moderate processing conditions they can be easily deposited not only on rigid glass substrates but also on flexible foils. They show high stability against humidity, light irradiation, and temperature, positioning themselves as good candidates for applications in OLEDs and OSCs. Eventually, by simulations and experiments it is verified that a moderate degree of variations in layer thickness and surface roughness can suppress side interference fringes, while not impacting the main transmittance minimum or the main reflection maximum, respectively.

Fully Solution‐Processed Photonic Structures from Inorganic/Organic Molecular Hybrid Materials and Commodity Polymers

“…Nevertheless, these mirrors often suffered from optical losses (scattering of particles and rough interfaces), poor control of the thicknesses, or the need for long UV or temperature curing steps. [1,10,15,[17][18][19][20][21][22]…”

Fabrication of Bragg Mirrors by Multilayer Inkjet Printing

“…The slight increase in the side interference peaks might result from the detuning of the Bragg mirror and the random thickness variation. [ 20a,29 ] Furthermore, the angle dependence of the fabricated Bragg mirror at 561 nm can be found in Figure S13 (Supporting Information), where a larger angle of incidence leads to a blue shift.…”

“…[ 19 ] Blade coating, on the other hand, can be used for large‐scale production; however, it is very challenging to have good control of the thin film quality. [ 20 ] Using self‐assembly is time‐consuming, and also it is hard to land with high reproducibility. [ 21 ] Moreover, the lateral definition of Bragg mirrors is not possible with any of the abovementioned approaches.…”

Prospects in Broadening the Application of Planar Solution‐Based Distributed Bragg Reflectors

“…In doctor blading, the excess of the coating solution is removed by moving either a blade or roll on the coated surface or moving the substrate below a stationary blade/roll. [17] Control of the film thickness can be achieved by adjusting the concentration of the coating solution, the speed of the moving blade/substrate, or the volume of the deposited solution. Bronnbauer sizes of DBRs on both glass and flexible PET foil substrates.…”