Site-specific chemical doping reveals electron atmospheres at the surfaces of organic semiconductor crystals.

Yan Wang,P Paul Ruden,Frank Würthner,Matthias Stolte,C Daniel Frisbie,Rebecca Renner,Tao He

doi:10.1038/s41563-021-01079-z

Abstract

Chemical doping controls the electronic properties of organic semiconductors, but so far, doping protocols and mechanisms are less developed than in conventional semiconductors. Here we describe a unique, site-specific, n-type surface doping mechanism for single crystals of two benchmark organic semiconductors that produces dramatic improvement in electron transport and provides unprecedented evidence for doping-induced space charge. The surface doping chemistry specifically targets crystallographic step edges, which are known electron traps, simultaneously passivating the traps and releasing itinerant electrons. The effect on electron transport is profound: field-effect electron mobility increases by as much as a factor of ten, and its temperature-dependent behaviour switches from thermally activated to band-like. Our findings suggest new site-specific strategies to dope organic semiconductors that differ from the conventional redox chemistry of randomly distributed substitutional impurities. Critically, they also verify the presence of doping-induced electron atmospheres, confirming long-standing expectations for organic systems from conventional solid-state theory.

Highlights

Chemical doping plays a central role in the science and applications of organic semiconductor materials[1,2,3,4,5,6]
We have discovered that doping-induced electron atmospheres along the step edges can be visualised by scanning Kelvin probe microscopy (SKPM)
The striking SKPM images represent the first direct detection of space charge associated with chemical doping in an organic semiconductor and provide critical verification of doping effects in organic systems that match expectations from classical inorganic semiconductor physics

Summary

Introduction

Chemical doping plays a central role in the science and applications of organic semiconductor materials[1,2,3,4,5,6]. We describe a unique, site-specific, n-type surface doping mechanism for single crystals of two benchmark organic semiconductors that produces dramatic improvement in electron transport and concurrently provides unprecedented evidence for doping-induced space charge.

Results

Conclusion