Crystallization and Polymorphism of Organic Semiconductor in Thin Film Induced by Surface Segregated Monolayers

Seiichiro Izawa,Kyohei Nakano,Kaori Suzuki,Daisuke Hashizume,Yujiao Chen,Thuc-Quyen Nguyen,Keisuke Tajima,Tomoka Kikitsu,Tomoyuki Koganezawa

doi:10.1038/s41598-017-18881-y

Abstract

Preparation of highly crystalline organic semiconductor films is vital to achieving high performance in electronic devices. Here we report that surface segregated monolayers (SSMs) on top of phenyl-C61-butyric acid methyl ester (PCBM) thin films induce crystal growth in the bulk, resulting in a dramatic change in the structure to form a new crystal phase. Highly ordered crystalline films with large domain sizes of several hundreds of nanometers are formed with uniaxial orientation of the crystal structure perpendicular to the substrate. The molecular rearrangements in SSMs trigger the nucleation at a lower temperature than that for the spontaneous nucleation in PCBM. The vertical charge mobility in the SSM-induced crystal domains of PCBM is five times higher than in the ordinary polycrystalline domains. Using surface monolayers may be a new strategy for controlling crystal structures and obtaining high-quality organic thin films by post-deposition crystallization.

Highlights

We have been developing surface segregated monolayers (SSMs) as a facile method for modifying the surface of organic semiconducting films
phenyl-C61butyric acid methyl ester (PCBM) is an n-type organic semiconductor extensively studied for OPVs24 and OFETs25
The results indicated that the oligosiloxane chains of pSi, bSi, and nSi were uniformly dispersed at the surface of the PCBM films

Summary

Introduction

We have been developing surface segregated monolayers (SSMs) as a facile method for modifying the surface of organic semiconducting films. Similar to the organic film/substrate interface, the surface of the films could be another nucleation site for controlling the crystallization in the bulk of the films, but free from the limitation in the choice of substrates. Note that this surface-induced crystallization can be significantly different from the conventional substrate-induced crystallization in term of the nucleation mechanism, since the molecules are much more mobile at the surface than at the substrate interfaces. The role of SSMs in the crystal growth of an organic semiconductor in thin films and their effects on the electronic conduction properties were investigated

Methods

Results

Conclusion