Hole transporting layer plays a crucial role to realize high efficiency and long lifespan by balancing the charge carrier into the desired recombination zone.

A new molecular design featuring a carbazole-derivative as an acceptor and a triphenylamine donor and displaying hybridized local and charge transfer (HLCT) fluorescence is demonstrated.

Wet-process enables organic light-emitting diodes (OLEDs) to be made cost-effectively via a continuous process, such as roll-to-roll manufacturing. Initially, wet-process based OLEDs used to be fabricated with polymer-based emitters and/or host materials. However, small molecules that can be processed using a wet-process are more promising for commercialization due to easier control over their molecular weight, purification, solution viscosity, layer thickness, and uniformity. We have hence reviewed herein (i) what constitutes the essential materials for wet-process feasible OLEDs, (ii) applicable wet-process technologies, and (iii) reported wet-processed mono- and polychromatic OLED devices with sound efficiency performance. And last, but not least, we have pointed out the most critical challenges that wet-processed electronics including OLED must face before gaining sufficient ground for competition and turning into disruptive technology. These include issues such as multiple-layer feasibility, film integrity, film forming capability, and device lifetime.

Six novel non-symmetric discotic liquid crystalline (DLC) dimers composed of pentaalkynylbenzene (PA) and triphenylene (TP) moieties were synthesized by using the CuI–Et₃N catalyzed click reaction between terminal TP alkyne and PA azide. All the compounds exhibit mesomorphic behaviour at room temperature. Pure compounds 8a–b (n = 6, 8 & m = 1) and 9a–b (n = 6, 8 & m = 3) display a columnar centered rectangular (Col_r) phase while 8c (n = 10, m = 1) and 9c (n = 10, m = 3) show a weak smectic (Sm) phase. Remarkably, the mesophase transforms from Col_r and Sm to columnar hexagonal (Col_h) on doping the pure compounds with electron-acceptor 2,4,7-trinitrofluorenone (TNF) molecules in a 2 : 1 TNF/compound ratio. The induction of stable Col_h mesomorphism is driven through charge-transfer interactions of electron-rich PA and TP moieties with electron-acceptor TNF molecules. The thermal behaviour of the compounds was studied through polarised optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) studies. The performed grazing incidence small and wide angle X-ray scattering (GISAXS/GIWAXS) study showed good alignment ability of 9a in the Col_r and complex 9a/TNF in the Col_h phase. Additional information about the arrangement of molecules in the Col_r and the Col_h 2D lattice is deduced by the construction of electron density maps (EDM). The pure non-symmetric dimers 8a–c and 9a–c were blue luminescent in the solution state and shifted to green in the solid state because of aggregation. Hence, the fabrication of doped OLED devices by using 8a and 9a as an emitter with the configuration ITO/PEDOT:PSS/host:emitter/TPBi/LiF/Al illustrates the restoration of the electroluminescence (EL) spectrum to narrow and a blue shifted photoluminescence (PL) spectrum, which indicates the suppression of aggregates. Emitters 8a and 9a are doped with three different hosts: (carbazolyl)-1,1′-biphenyl (CBP), 4′,4′′-tri(N-carbazolyl)triphenylamine (TCTA) and 2,7-bis(carbazol-9-yl)-9,9-spirobifluorene (Spiro-2CBP), by varying the dopant concentration. The best EL performance is observed for the device fabricated with 8a (5 wt% in the CBP host) and 9a (3 wt% in the CBP host) with a maximum external quantum efficiency (EQE) of 2.1% and CIE coordinates of (0.16, 0.10). One of the studied complexes 8b/TNF exhibited an ambipolar charge carrier mobility of 1.78 × 10⁻³ cm² V⁻¹ s⁻¹ and 1.25 × 10⁻³ cm² V⁻¹ s⁻¹ for electrons and holes, respectively, at room temperature. The observed ambipolar mobility of the complex compound reveals its potential application as an organic semiconducting material.