Control of Molecular Orientation in Organic Semiconductor Films using Weak Hydrogen Bonds

Abstract

Use of the intrinsic optoelectronic functions of organic semiconductor films has not yet reached its full potential, mainly because of the primitive methodology used to control the molecular aggregation state in amorphous films during vapor deposition. Here, a universal molecular engineering methodology is presented to control molecular orientation; this methodology strategically uses noncovalent, intermolecular weak hydrogen bonds in a series of oligopyridine derivatives. A key is to use two bipyridin‐3‐ylphenyl moieties, which form self‐complementary intermolecular weak hydrogen bonds, and which do not induce unfavorable crystallization. Another key is to incorporate a planar anisotropic molecular shape by reducing the steric hindrance of the core structure for inducing π–π interactions. These synergetic effects enhance horizontal orientation in amorphous organic semiconductor films and significantly increasing electron mobility. Through this evaluation process, an oligopyridine derivative is selected as an electron‐transporter, and successfully develops highly efficient and stable deep‐red organic light‐emitting devices as a proof‐of‐concept.

New exciplex systems composed of triazatruxene donors and N-heteroarene-cored acceptors

“…The data are summarized in Table 1. The absorption spectra of 3P-T2P and 3P-Pyr show similar results with the absorption peaks at around 259 and 325 nm, which could be attributed to the p-p* transition and n-p* transition, 34,35 respectively. The absorption edge can be unambiguously assigned to determine the optical energy gap to be 3.58, 3.50 and 3.63 eV for 3P-T2T, 3P-T2P and 3P-Pyr, respectively.…”

H‐Bonds‐Assisted Molecular Order Manipulation of Nonfullerene Acceptors for Efficient Nonannealed Organic Solar Cells

“…Unlike preceding substituents, the hydroxyl group is seldom incorporated into organic semiconductors, likely owing to its high polarity and chemical activity . On the other hand, the hydroxyl is widespread in the nature and in biological system, where it can form hydrogen bonds (H‐bonds) with lone‐pair electron‐containing atoms, triggering self‐assembly processes, and ordered structures, which is also involved in many research areas . Thus, introducing the hydroxyl into the ITIC‐based acceptor is highly potential to improve the molecular packing and crystallinity via forming intermolecular H‐bonds.…”

Molecular Orientations of Delayed Fluorescent Emitters in a Series of Carbazole-Based Host Materials

“…As mentioned above, although a high value of up to 100% at 200 K has been reported, the underlying mechanism to realize horizontal orientation is still under discussion at this stage (Yokoyama, 2011;Mayr and Brütting, 2015;Moon et al, 2015;Shibata et al, 2015;Friederich et al, 2017;Schmidt et al, 2017;Gujral et al, 2018;Kim and Kim, 2018;Lee et al, 2018;Pal et al, 2018;Watanabe et al, 2019b). In order to deepen insights into the underlying mechanism, we wish to report a systematic investigation on the molecular orientations of TADF molecules in a series of carbazole-based host materials.…”

“…To obtain such a high-performance in OLEDs, horizontal orientation of the emission dipole moment (EDM) is absolutely essential. Perfect horizontal orientation of the EDM has been reported to boost OLED efficiency up to 150% compared to random EDM orientation (Frischeisen et al, 2011;Yokoyama, 2011;Schmidt et al, 2017;Kim and Kim, 2018;Watanabe et al, 2019b). However, the horizontal orientation ratio ( ) of most TADF emitters used in OLEDs realizing η ext over 30% is reportedly only around 80%, which is far behind perfect horizontal orientation ( = 100%).…”