The Root Causes of the Limited Electroluminescence Stability of Solution-Coated Versus Vacuum-Deposited Small-Molecule OLEDs: A Mini-Review

Abstract

Using solution-coating methods for the fabrication of organic light-emitting devices (OLEDs) offers a tremendous opportunity for enabling low-cost products and new applications. The electroluminescence (EL) stability of solution-coated (SOL) OLEDs, however, is significantly lower than that of vacuum-deposited (VAC) OLEDs, causing their operational lifetimes to be much shorter—an issue that continues to hamper their commercialization. The root causes of the lower EL stability of these devices remain unclear. This article briefly reviews and summarizes some of the work that has been done to-date for elucidating the root cause of the lower EL stability of SOL OLEDs, giving special attention to studies where side-by-side comparisons of SOL and VAC devices of the same materials have been conducted. Such comparisons allow for more-reliable conclusions about the specific effects of the solution-coating process on device stability to be made. The mini-review is intended to introduce the work done to-date on the causes of lower stability in SOL OLEDs and to stimulate further work for the purpose of closing the existing knowledge gap in this area and surmounting this long-standing challenge in the SOL OLED technology.

Recent endeavors and perspectives in developing solution-processable host materials for thermally activated delayed fluorescence organic light-emitting diodes

“…72,77 On the other hand, the electron transporters include triazine, phosphine oxide (PQO), borane derivatives, carbonyl, sulfonyl, pyridine, and cyano groups. Due to the lack of electron-acceptors, Godumala et al introduced two new acceptors, namely, benzo [4,5] 21 and chromenopyrazole (CP), 22 which showed prominent features such as a high E T and excellent solubility in common organic solvents.…”

“…Therefore, it is essential to introduce novel potential acceptor moieties that will be useful to the materials science community. Godumala et al introduced a new electronacceptor core, benzo [4,5]imidazo[2,1-b][1,3]thiazine (BBIT), and developed two new solution-processable host materials (CzBBIT and CzBBIT) (Scheme 2). 21a Before understanding the ability of BBIT to function as an electron acceptor, density functional theory (DFT) and time-dependent DFT (TD-DFT) studies were carried out (Fig.…”

“…1 OLEDs offer significant advantages over previous liquid crystal display (LCD) technologies like enhanced picture quality due to the improved color contrast ratio and the possibility of fabricating flexible devices. [2][3][4][5] Thermally activated delayed fluorescence (TADF) materials have attracted tremendous attention in the field of OLEDs. Compared to conventional fluorescent and phosphorescent materials, [6][7][8][9] TADF emitters have the ability to harness both singlet and triplet excitons through reverse intersystem crossing (RISC) facilitated by their intrinsically small singlet-triplet energy gap (DE ST ), resulting in 100% internal quantum efficiency (ISC).…”

Molecularly engineered host materials for high performance inkjet-printed thermally activated delayed fluorescence organic light-emitting diodes

“…7 However, to date, TADFbased OLEDs have been mainly fabricated by vacuum deposition processes. 11,12 Compared to vacuum-processing techniques, which are limited by poor material yield and insufficient thickness homogeneity on large substrates, [13][14][15] solution-processing techniques are more competitive in low-cost and large-scale OLED fabrication. 14,[16][17][18][19] Among various solution-processing techniques, inkjet printing (IJP) is of great interest, especially in the display industry, for its high material utilization, accurate deposition, and direct patternability.…”

Pyridine-Annulated Functional Fused Indole as a Hole Transport Material for Solution-Processed OLEDs

“…7,8 The vacuumdeposited fabrication of OLEDs has been established as a highly effective technique to obtain high-performing devices. 9 However, low material utilization, high manufacturing costs, and limited deposited space often limit the advancement of vacuum-deposited techniques and increase the cost of the final products. 8,10 Therefore, the development of solution-processed OLEDs has been greatly enhanced over the past few years.…”