Designing Host Materials for the Emissive Layer of Single‐Layer Phosphorescent Organic Light‐Emitting Diodes: Toward Simplified Organic Devices

Abstract

Thanks to the tremendous effort over the last 20 years, phosphorescent organic light‐emitting diodes (PhOLEDs) represent a prevalent technology. In this technology, all the high‐efficiency PhOLEDs are multi‐layer devices constituting, in addition to the emissive layer (EML), of a stack of functional organic layers. These layers play a crucial role in the device performance as they improve the injection, transport, and recombination of charges within the EML. Single‐layer PhOLEDs (SL‐PhOLEDs) represent ideal OLEDs, consisting only of the electrodes and the EML. However, reaching high‐performance SL‐PhOLED is far from easy, as removing the functional layers of an OLED stack dramatically decreases the performance. To achieve high SL‐PhOLED efficiency, the efficient injection, transport, and recombination of charges should be insured by the EML, and particularly, by the host material. In the present exhaustive review, the different molecular design strategies are analyzed, which have been used to construct high‐efficiency hosts for SL‐PhOLED. The impact of the electronic properties (triplet energy, HOMO/LUMO energy, mobility etc.) on the device characteristics (threshold voltage, electroluminescent spectrum, external quantum efficiency, etc.) are discussed. This allows to draw a structure/properties/device performance relationship map of interest for the future design of functional materials for SL‐PhOLEDs.

Quinolinophenothiazine as an electron rich fragment for high efficiency RGB single-layer phosphorescent organic light-emitting diodes

“…One of the key feature in the new generations of simplified SL-PhOLEDs is the capability of the host matrix to efficiently transport both type of charges, hole and electron. 23 As PhOLEDs are vertical stacks, space charge limited current (SCLC) devices are the most appropriate to probe the charge carrier mobilities. Herein, hole-only and electron-only devices have been fabricated and characterized providing the out-of-plane hole and electron mobilities respectively (Figure 6, see SI for technical details).…”

“…17 However, this molecular fragment, described more than 40 years ago, 21 has never been used in the new generation of simplified PhOLEDs so-called single-layer. For the last twenty years, simplifying fluorescent 22 and phosphorescent OLEDs 23 has indeed attracted the attention of many research groups worldwide. The goal is to bridge the gap between multi-layer PhOLEDs, which are highly efficient and widely described nowadays in literature 11,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] and the new generation of single-layer PhOLEDs (SL-PhOLEDs), which still presents low performance except for a few examples.…”

“…The goal is to bridge the gap between multi-layer PhOLEDs, which are highly efficient and widely described nowadays in literature 11,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] and the new generation of single-layer PhOLEDs (SL-PhOLEDs), which still presents low performance except for a few examples. 7,23,[41][42][43] Simplifying PhOLEDs will notably reduce the inherent complexity of the stack and its cost. More importantly, for the future ecological transition, simplifying electronic devices will help to reduce its environmental footprint.…”

Journal of Materials Chemistry C Editor's choice web collection: ‘Spiro compounds for electronics’

“…For the last ten years, the spiro architecture has been particularly used to design host materials for phosphorescent OLEDs 5 and for thermally activated delayed fluorescence (TADF) OLEDs. 6,7 Indeed, in these two technologies, the host material usually gathers an electron-rich and electron-poor fragment and these two fragments should be spatially separated.…”

meta-Terphenyl linked donor–π–acceptor dyads: intramolecular charge transfer controlled by electron acceptor group tuning

“…[1][2][3][4][5][6][7][8][9] In particular, donor-p-acceptor (D-p-A) dyad molecules are widely used molecular systems because of the easy tailoring of the photophysical property by changing the sub-units such as donor, acceptor, and p-linker. Thus, an adequate combination of sub-units in the D-p-A dyad system is the key to achieving the desired electrochemical and photophysical properties for a wide range of applications, such as organic light-emitting diodes (OLEDs), [10][11][12][13][14][15][16][17] dye-sensitized solar cells (DSSCs), [18][19][20][21] organic photovoltaics (OPVs), [22][23][24] photoelectrochemical cells (PECs), [25][26][27][28] uorescence sensors, [29][30][31] mechanochromic materials, [32][33][34] nonlinear optical materials, 35,36 and nanostructured materials. [37][38][39] The notable features of D-p-A dyads are intramolecular charge transfer (ICT) and photoinduced electron transfer (PET) in the ground and excited states because of the large electronic dipoles.…”