# POLED displays: Robust printing of pixels

## TL;DR

This paper develops a combined experimental and numerical approach to optimize the printing protocols for uniform fluid deposition in POLED display pixels, accounting for surface wetting properties and substrate imperfections.

## Contribution

It introduces a predictive Cox-Voinov law-based model to guide efficient printing strategies for high-quality POLED display fabrication.

## Key findings

- Model accurately predicts liquid evolution in pixels.
- Provides a cost-effective tool for designing printing protocols.
- Accounts for substrate and printhead uncertainties.

## Abstract

The fabrication of a high-quality POLED (Polymeric Organic Light Emitting Diode) display requires the deposition of identical, uniform fluid films into a large number of shallow recessed regions that form a regular array of pixels on a display backplane. We determine the protocols required to achieve continuous liquid coverage of the entire pixel area for the case where equally-spaced fluid droplets are sequentially printed along a straight line within a stadium-shaped pixel, and explore how these protocols depend on the wetting properties of the pixel surface. Our investigation uses a combination of experiments and numerical modelling, based on the assumption of fluid redistribution via capillary spreading according to a Cox-Voinov law. We show that the model is able to predict quantitatively the evolution of the liquid deposited in a pixel and provides a computationally inexpensive design tool to determine efficient printing strategies that account for uncertainties arising from imperfect substrate preparation or printhead dysfunction.