Hydrophenazine-linked 2D Ladder-type Crystalline Fused Aromatic Network with High Charge Transport

Abstract
Since the advent of graphene, the development of crystalline twodimensional (2D) organic materials with semiconducting features has been extensively explored for their potential optoelectronic applications. Despite extensive progress in this field, it is still challenging to realize laterally extended organic materials with high electrical transport properties. Here, we report a 2D ladder-type fused aromatic network (FAN) in which backbones are composed of hydrophenazine (HP) linkage (designated HP-FAN). Consequently, its 2D extended delocalization of p-molecular orbitals imparts a semiconducting band gap and facilitates fast intra-chain charge transport. The as-prepared HPFAN exhibits semiconducting features with calculated and experimental band gaps of approximately 1.44 and 1.54 eV, respectively, with an unusual flat band. The HP-FAN thin flakes, isolated by polydimethylsiloxane stamping, exhibit remarkable performance in a p-type field-effect transistor (FET) and a Hall effect device. Given its laterally extended ladder-type p-conjugated structure, the HP-FAN has extensive potential for applications in thin-film optoelectronic devices.

A research team, led by Professor Jong-Beom Baek in the School of Energy and Chemical Engineering at UNIST has succeeded in synthesizing a unique ladder-type hydrophenazine (HP)-linked fused aromatic network (HP-FAN), a new breed of 2D polymers (2DPs), whose macromolecular backbones are formed of uninterrupted fused HP rings via aromatization reaction.

Figure 1. Schematic image of the ladder-type hydrophenazine-linked 2D fused aromatic network.

According to the research team, the proposed HP-FAN films are demonstrated to exhibit a semiconducting band gap with a unique flat band, along with high conductivity, facile charge transport properties, and structural rigidity. In addition, they demonstrate remarkable performances as electronic devices with high mobility and on/off current ratio, and thus are expected to provide a significant leap in the design and further advance in semiconducting 2D polymers.

“The present work sheds light on the synthesis of unique ladder-type crystalline 2DPs for future potential optoelectronic devices and explores their charge transport features,” noted the research team.

Figure 2. Images of HP-FAN films, fabricated on a silicon wafer substrate.

This study has been carried out in collaboration with Professor Kilwon Cho and his research team in the Department of Chemical Engineering at POSTECH. Their findings have been published in the August 2022 issue of Chem, a sister journal to Cell. It has been supported by the Creative Research Initiative (CRI), Science Research Center (SRC), and Young Researcher programs through the National Research Foundation (NRF) of Korea. This study has also been supported by the U-K brand project of UNIST.

Journal Reference
Hyuk-Jun Noh, Sein Chung, Mahmut Sait Okyay, et al., “Hydrophenazine-linked two-dimensional ladder-type crystalline fused aromatic network with high charge transport,” Chem, (2022).