Development of Efficient OLEDs from Solution Deposition

Summary

Presented here is a protocol for the fabrication of efficient, simple, solution-deposited organic light-emitting diodes with low roll-off.

Abstract

The use of highly efficient organic emitters based on the thermally activated delayed fluorescence (TADF) concept is interesting due to their 100% internal quantum efficiency. Presented here is a solution deposition method for the fabrication of efficient organic light-emitting diodes (OLEDs) based on a TADF emitter in a simple device structure. This fast, low-cost, and efficient process can be used for all OLED emissive layers that follow the host-guest concept. The fundamental steps are described along with necessary information for further reproduction. The goal to establish a general protocol that can be easily adapted for principal organic emitters currently under study and development.

Introduction

The increase in organic electronics used in daily life has become an unsurpassed reality. Among several organic electronic applications, OLEDs are perhaps the most attractive. Their image quality, resolution, and color purity have made OLEDs a primary choice for displays. Moreover, the possibility to achieve large area emission in extremely thin, flexible, lightweight, and easy color-tunable OLEDs has applications in lighting. However, some technological issues associated with the fabrication process in large area emitters have postponed further application.

With the first OLED working at low applied voltages¹, new p....

Protocol

CAUTION: The following steps involve the use of different solvents and organic materials, so proper care must be taken when handling. Use the fume hood and protective equipment such as lab glasses, face masks, gloves, and lab coats. Weighing of the materials should be done precisely using a high precision scale machine. To ensure cleanliness of the substrates, solution deposition of thin films, and evaporation, it is recommended that all the procedures be performed in a controlled environment or glovebox. Before the use of a spin-coater, micropipettes, thermal evaporators, organic materials, and solvents, all safety data sheets must be consulted.

Results

Figure 5 shows the main results for the fabricated device. The turn-on voltage was extremely low (~3 V), which is an interesting result for a two organic layer device. The maximum brightness was around 8,000 cd/m² without using an integrating sphere. The maximum values for η_c, η_p, and EQE were around 16 cd/A, 10 lm/W, and 8%, respectively. Although the results are not the best figures of merits for this TADF emitter, they were the best found in such a simple .......

Discussion

The protocol used here to fabricate an efficient OLED in a simple device structure is relatively simple. The electrical mobility is not only modulated by the material composition of a device layer but also critically depends on film morphology. Preparation of the solutions and a suitable choice of solvent and concentration are important. No material aggregation can occur, implying complete solubility at the nanometric scale. It is also important to observe the viscosity of the solution. A high viscosity leads to a high c.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
2PXZ-OXD (2,5-bis(4-(10H-phenoxazin-10-yl)phenyl)-1,3,4-oxadiazole)	Lumtec ltd	1447998-13-1
Aluminum (99.999%)	Alfa Aesar	7429-90-5
Acetone (99.9%)	Sigma Aldrich	67-64-1
Hellmanex	Ossila	7778-53-2
Isopropyl alcohol	Sigma Aldrich	67-63-0
ITO patterned substrates	Ossila	65997-17-3
Lithium Fluoride (99.99%)	Sigma Aldrich	7789-24-4
OXD-7 (1,3-Bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazo-5-yl]benzene)	Ossila	138372-67-5
PEDOT: PSS (Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate)	Ossila	155090-83-8
PVK (Polyvinlycarbazole) (average Mn 25,000-50,000)	Sigma Aldrich	25067-59-8
TmPyPb (1,3,5-Tri(m-pyridin-3-ylphenyl)benzene)	Ossila	138372-67-5