Structural optimization of slot-die heads with T-shaped cavity for fabrication of large-area OLEDs

With an attempt to achieve highly uniform large-area organic thin films for potential applications in solutionprocessable organic light-emitting diodes (OLEDs), we have optimized the structure of slot-die heads with Tshaped cavity (manifold) by computational fluid dynamics (CFD) simulation. Depending on the viscosity of coating solutions, the pressure distribution inside the cavity and the velocity distribution at the outlet are analyzed by varying the structure parameters such as the shim thickness, cavity volume (cavity depth, cavity height, cavity width), and land length. From CFD simulation results, we have derived the maximum shim thickness at which the pressure non-uniformity becomes less than 5 %, which can provide a simple and intuitive design guideline. It is addressed that the maximum shim thickness is most affected by the cavity width, followed by the cross-sectional area of the cavity and then the land length. Using the structurally optimized slot-die head, we have carried out slot-die coating of low-viscosity (80 cPs) poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) and high-viscosity (4,800 cPs) polydimethylsiloxane (PDMS) and achieved thin films with the thickness non-uniformity less than 10 %. Furthermore, we have successfully fabricated 120 mm x 20 mm OLED devices with the slot-coated conductive PEDOT:PSS layer, exhibiting the luminance of 801 cd/m2 at 6 V.