Step-by-Step Guide for Harnessing Organic Light Emitting Diodes by Solution Processed Device Fabrication of a TADF Emitter

Summary

Organic Light Emitting Diode (OLED) devices offer superior display quality with better contrast while propounding environmental benefits by lower energy consumption. Here, a simple strategy for the solution-processed OLED device fabrication is presented in a sequential manner.

Abstract

The demand for energy-efficient light sources has witnessed a significant surge in the recent era, due to the increasing awareness towards environmental concerns and climate change. Organic Light Emitting Diodes (OLEDs) offer superior display quality, energy efficiency, and sustainability, which makes them an ideal choice for eco-conscious consumers and reduced carbon footprint-based industries. The thinner and more flexible OLEDs have revolutionized the field of smartphones, televisions, automotive displays, and wearable gadgets. Here, in this paper, an efficient OLED device is fabricated starting from the synthesis of a donor-acceptor-based emitter, followed by its purification. The organic synthesis process is explained briefly. For purification, firstly, the product mixture is purified by column chromatography, and then it is sublimed using a temperature gradient vacuum sublimation set-up to obtain a high-purity compound. The ultimate goal is to make a multi-layered OLED device that needs ultra-high-purity emitters. Making an efficient OLED needs precision and expertise; thus, showcasing a detailed step-by-step protocol is important to the science community. Here, the details about the solution-processed OLED device fabrication is unfolded in four steps (substrate cleaning, spin coating of layers, thermal evaporation of layers, and device performance measurement). First, the substrates need to be cleaned using a well-established protocol. Next, the layered architecture is obtained by spin coating and thermal deposition of desired materials to the required thickness. The thermal evaporation is done using a high vacuum thermal evaporator with an integrated glove box setup. Finally, to obtain the device's performance, measurements are to be carried out in a dark environment. This comprehensive work will provide in-depth knowledge of device fabrication and inspire more researchers towards decorating this world with OLEDs.

Introduction

With the increasing modernization, the rate of energy consumption has brimmed over, which has compelled the emergence of several energy-efficient sources. Although it is often unrealized, lighting is one of the major power-consuming fields. According to a report published by the United Nations Environment Program (UNEP) in 2017¹. Lighting consumes 15-19% of global electricity^1,2 and emits around 5% of greenhouse gases in the world^1,3. If this issue is left unattended, then electricity consumption for lighting will increase manyf....

Protocol

NOTE: Devices are very sensitive to dust and foreign particles; any kind of impurity can alter the actual performance of the emitter and can potentially lead to non-functioning or short circuits in the device. So, these need to be made in a clean place with utmost precautions. It is advised to prepare the devices inside the glove box with a controlled moisture and oxygen environment (oxygen and moisture level 0.1 ppm).

1. Emitter synthetic strategy

1. Find a suitable design for a donor-acceptor-based TADF molecule with the help of a literature survey. Scrutinize the proposed structure through theoretical calculatio....

Results

Figure 3A shows the arrangement of all the crucibles (or boats) inside the thermal evaporator and the materials used in their respective positions. The setup contains 10 boats, which means at most 10 different materials can be loaded. Figure 3B shows the position of all six sensors. These Quartz Crystal Microbalance (QCM) sensors help to determine the real thickness values of evaporated layers.

Discussion

The above procedure serves as a comprehensive guide for the synthetic strategy of a TADF molecule, purification, solution-processed device fabrication, and characterization of OLEDs. The OLED device was fabricated by facile solution-processing⁴⁰ of the emissive layer. This results in low cost and easy control of the weight percentage of the host in the emissive layer. This method also allows easy scalability of the device and facile integration to flexible substrates, along with better control ove.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
13 mm X 0.22 μm  PVDF syringe filter	BSB Pharma	BSBPTF1345
13 mm X 0.45 μm  PTFE syringe filter	BSB Pharma	BSBPV1345
2,2′,2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1H-benzimidazole) (TPBi)	BLD Pharma	BD234896	Sublimed
8-Hydroxyquinolinolato-lithium (Liq)	BLD Pharma	BD446731	Sublimed
Acetone	Purechem		used as such
Aluminum pellet	Kurt J. Lesker	EVMAL50EXQD	99.999% pure
Chlorobenzene	Spectrochem	10342	>99% puriss AR
Hellmanex III soap solution	Sigma -Aldrich	Z805939	used 1% (v/v) soap solution
Isopropyl alcohol	Purechem		used as such
ITO patterned Glass Substrate	Zhuhai Kaivo Optoelectronic Technology Co.,Ltd.	Item no. 004-1520-SK	Sheet resistance<17ohm/sq, size=15*20*1.1mm, Transmittance>82%
N,N′-Dicarbazolyl-4,4′-biphenyl (CBP)	BLD Pharma	BD21599	Sublimed
PEDOT:PSS	Ossila (bought)	Clevios P VP AI 4083
Poly(9-vinylcarbazole) (PVK)	Sigma -Aldrich	182605	average Mw ~1,100,000, used as such
Toluene	Spectrochem	52035	Spectroscopy Grade