p-Doping of Copper(I) Thiocyanate (CuSCN) Hole-Transport Layers for High-Performance Transistors and Organic Solar Cells

Abstract

The ability to tune the electronic properties of soluble wide bandgap semiconductors is crucial for their successful implementation as carrier-selective interlayers in large area opto/electronics. Herein the simple, economical, and effective p-doping of one of the most promising transparent semiconductors, copper(I) thiocyanate (CuSCN), using C60F48 is reported. Theoretical calculations combined with experimental measurements are used to elucidate the electronic band structure and density of states of the constituent materials and their blends. Obtained results reveal that although the bandgap (3.85 eV) and valence band maximum (−5.4 eV) of CuSCN remain unaffected, its Fermi energy shifts toward the valence band edge upon C60F48 addition—an observation consistent with p-type doping. Transistor measurements confirm the p-doping effect while revealing a tenfold increase in the channel's hole mobility (up to 0.18 cm2 V−1 s−1), accompanied by a dramatic improvement in the transistor's bias-stress stability. Application of CuSCN:C60F48 as the hole-transport layer (HTL) in organic photovoltaics yields devices with higher power conversion efficiency, improved fill factor, higher shunt resistance, and lower series resistance and dark current, as compared to control devices based on pristine CuSCN or commercially available HTLs.