Essential Differences of Organic Films at the Molecular Level via Vacuum Deposition and Solution Processes for Organic Light-Emitting Diodes

Abstract

This paper presents an in-depth understanding of the essential differences of organic small-molecule thin films at the molecular level via vacuum deposition and solution processes for organic light-emitting diodes (OLEDs). Synchrotron-based two-dimensional grazing incidence X-ray diffraction has been used to investigate the essential difference. The result reveals that tris(4-carbazoyl-9-ylphenyl)amine (TCTA) molecules show highly oriented arrangements, that is, face-to-face π−π stacking, in vacuum-deposited films, unlike the randomly arranged molecules in spin-coated films. The faceto-face π−π stacking behavior of the molecules in a vacuum-deposited TCTA film leads to higher hole-transport mobility, which is the essential reason for the higher efficiency of a vacuum-deposited OLED compared with that of a solution-processed counterpart, consistent with the calculation results.

Copper(I) thiocyanate (CuSCN) as a hole-transport material for large-area opto/electronics

“…The device architecture of solution-processed, multilayer, bottom-emitting, phosphorescent green OLEDs from the earlier study is illustrated in figure 14 [63]. Meanwhile, figure 15 Despite the much promising achievements, however, solution-processed OLEDs incorporating CuSCN as the HIL/HTL are yet unable to compete with state-of-the-art vacuum-processed OLEDs [160,169]. It is certain however that further optimization of solution-processable interlayer technologies based on CuSCN, as well as other materials systems, is expected to improve the efficiency of solution-processed OLEDs, and potentially enable use of the technology in a range of inexpensive lighting applications.…”

Controllable molecular configuration for significant improvement of blue OLEDs based on novel twisted anthracene derivatives

“…5a, the maximum emission (l max ) of p-PABPI and m-PABPI are located at 456 and 448 nm, and the full width at half-maximum (FWHM) values are located at 59 and 60 nm, respectively. There is a little red-shift for both, relative to photoluminescent (PL) spectra, which can be attributed to face-to-face pep stacking for the vacuum-deposited film [29]. The current density-voltage-luminance characteristics of the devices are given in Fig.…”

Supramolecular Architecture and Electrical Properties of a Perylene Derivative in Physical Vapor Deposited Films

“…In particular, PVD is one of the most common deposition technologies of small organic molecules, displaying high control on the supramolecular architecture of the films 24,25 Indeed, the molecular organization plays an important role and mediates the electrical and optical properties of the films toward optimization of the device performance 26 . The relevance of the technique can be understood from the results found in the manufacture of organic light emitting diodes (OLEDs) 27 and transistors, 28 for instance. Greater efficiency in charge mobility was found for films produced via PVD, which is a direct consequence of the molecular orientation, given by the face-to-face stacking of the deposited molecules 27 .…”

“…The relevance of the technique can be understood from the results found in the manufacture of organic light emitting diodes (OLEDs) 27 and transistors, 28 for instance. Greater efficiency in charge mobility was found for films produced via PVD, which is a direct consequence of the molecular orientation, given by the face-to-face stacking of the deposited molecules 27 . Therefore, the elucidation of the supramolecular architecture of thin films is crucial, prior to technological applications.…”