Transient phases during fast crystallization of organic thin films from solution

TL;DR

This study investigates the transient phases during rapid solution-based crystallization of an organic semiconductor, revealing a sequence of phases that enable high-speed processing and high mobility in thin films.

Contribution

It uncovers the transient crystallization phases of C8-BTBT during fast solution deposition and demonstrates a method to achieve large grains and high mobility at high speeds.

Findings

Transient phases include layered smectic liquid-crystalline and transient crystalline phases.

High-speed writing (25 mm/s) yields mobilities up to 3.0 cm²/V-s.

Method enables large grain size and high mobility in organic thin films.

Abstract

We report an in-situ microbeam grazing incidence X-ray scattering study of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C$_8$-BTBT) organic semiconductor thin film deposition by hollow pen writing. Multiple transient phases are observed during the crystallization for substrate temperatures up to $\approx$93$^\circ$C. The layered smectic liquid-crystalline phase of C$_8$-BTBT initially forms and preceedes inter-layer ordering, followed by a transient crystalline phase for temperature $>$60$^\circ$C, and ultimately the stable phase. Based on these results, we demonstrate a method to produce extremely large grain size and high carrier mobility during high-speed processing. For high writing speed (25 mm/s) mobility up to 3.0 cm$^2$/V-s has been observed.