Elucidating the Coordination of Diethyl Sulfide Molecules in Copper(I) Thiocyanate (CuSCN) Thin Films and Improving Hole Transport by Antisolvent Treatment

• Published in: Advanced functional materials Vol. 30; no. 36
• Main Authors: Worakajit, Pimpisut, Hamada, Fumiya, Sahu, Debashis, Kidkhunthod, Pinit, Sudyoadsuk, Taweesak, Promarak, Vinich, Harding, David J., Packwood, Daniel M., Saeki, Akinori, Pattanasattayavong, Pichaya
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.09.2020
• Subjects: Acetone; antisolvents; Bonding strength; Coordination polymers; Copper; copper(I) thiocyanate; Crystal structure; Crystallinity; Crystallites; Density functional theory; diethyl sulfide; Hole mobility; hole transport; Materials science; Microstructure; Morphology; Photovoltaic cells; Solar cells; Tetrahydrofuran; Thin films; Thiocyanates; Transistors
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202002355

Copper(I) thiocyanate (CuSCN) is rising to prominence as a hole‐transporting semiconductor in various opto/electronic applications. Its unique combination of good hole mobility, high optical transparency, and solution‐processability renders it a promising hole‐transport layer for solar cells and p‐type channel in thin‐film transistors. CuSCN is typically deposited from sulfide‐based solutions with diethyl sulfide (DES) being the most widely used. However, little is known regarding the effects of DES on CuSCN films despite the fact that DES can coordinate with Cu(I) and result in a different coordination polymer having a distinct crystal structure when fully coordinated. Herein, the coordination of DES in CuSCN films is thoroughly investigated with a suite of characterization techniques as well as density functional theory. This study reveals that DES directly affects the microstructure of CuSCN by stabilizing the polar crystalline surfaces via the formation of strong coordination bonds. Furthermore, a simple antisolvent treatment is demonstrated to be effective at modifying the microstructure and morphology of CuSCN films. The treatment with tetrahydrofuran or acetone leads to uniform films consisting of CuSCN crystallites with high crystallinity and their surfaces passivated by DES molecules, resulting in an increase in the hole mobility from 0.01 to 0.05 cm2 V−1 s−1. Diethyl sulfide (DES), commonly used as a solvent for the deposition of copper(I) thiocyanate (CuSCN), is found to coordinate strongly to polar Cu‐terminated surfaces of CuSCN. Thin films of CuSCN consist of nanoscale hexagonal prismatic crystallites with their surfaces passivated by DES. A simple antisolvent treatment is demonstrated to improve the crystallinity and enhance the hole mobility fivefold.