Effective hole transport layer structure for top-emitting organic light emitting devices based on laser transfer patterning

The design and preparation of top-emitting organic light emitting devices with thick hole transport layers that effectively smooth the substrate were performed. Bilayer transfer with laser thermal patterning method was used to simplify the fabrication of hole transport layers with various thicknesses, with the aim of optimizing the cavity effect in the top-emitting devices. By carrying out optical simulations and experiments, the optimal thicknesses of the hole transport layers for our structure of blue, green and red devices were found to be 140 nm, 160 nm and 230 nm, respectively. We have briefly illustrated the underlying device physics of top-emission in terms of the resonance and microcavity effect. The resulting top-emitting devices with thick hole transport layers exhibit better colour purity than bottom-emitting devices and satisfactory luminous efficiency. The relatively high operating voltages can be further improved by the use of transport materials with enhanced charge mobility.