Yamada Keitaro, Suzuki Mitsuharu, Suenobu Tomoyoshi, Nakayama Ken-Ichi
Department of Material and Life Science, Graduate School of Engineering , Osaka University , 2-1 Yamadaoka , Suita , Osaka 565-0871 , Japan.
ACS Appl Mater Interfaces. 2020 Feb 26;12(8):9489-9497. doi: 10.1021/acsami.9b18993. Epub 2020 Feb 17.
High vertical carrier mobilities in organic semiconductor films are a challenging issue for fundamentally improving the performance of vertical devices. To achieve improvement in the vertical direction, a reduced graphene oxide (rGO) template is used with pentacene and DNTT having a herringbone structure enabling two-dimensional (2D) transport in comparison with CuPc having a slipped-stack structure. A thin-film structure and the optoelectrical properties of the oriented films are investigated with respect to molecular structures and packing modes. The rGO template induces a "laid-down" herringbone structure for pentacene and DNTT with a face-on orientation. Our results reveal that intermolecular dispersion energy is an additional important factor to form face-on states of molecules and influences face-on ratios in the films on rGO. Vertical charge mobilities of the films are significantly enhanced by the rGO template. Particularly, the DNTT film with a laid-down herringbone structure produces a vertical mobility as high as 0.27 cm V s, one of the highest values for ordinary thin films with several hundred nanometer thickness. These findings suggest that 2D transport is advantageous for vertical carrier transport also.
对于从根本上提高垂直器件的性能而言，有机半导体薄膜中高的垂直载流子迁移率是一个具有挑战性的问题。为了在垂直方向上实现性能提升，使用了还原氧化石墨烯（rGO）模板与具有鱼骨状结构的并五苯和DNTT，与具有滑移堆积结构的CuPc相比，这种结构能够实现二维（2D）传输。针对分子结构和堆积模式，研究了薄膜结构以及取向薄膜的光电特性。rGO模板诱导并五苯和DNTT形成具有面朝上取向的“平躺”鱼骨状结构。我们的结果表明，分子间色散能是形成分子面朝上状态的另一个重要因素，并影响rGO上薄膜的面朝上比例。rGO模板显著提高了薄膜的垂直电荷迁移率。特别是，具有平躺鱼骨状结构的DNTT薄膜产生了高达0.27 cm² V⁻¹ s⁻¹的垂直迁移率，这是几百纳米厚的普通薄膜的最高值之一。这些发现表明，二维传输对于垂直载流子传输也是有利的。
