High charge-carrier mobility and low trap density in a rubrene derivative

TL;DR

This study reports the synthesis and characterization of a rubrene derivative with t-butyl groups, revealing high in-plane hole mobility and low trap density in one crystalline phase, advancing organic semiconductor performance.

Contribution

The paper introduces a new rubrene derivative with t-butyl groups, demonstrating high mobility and low trap density, and identifies two crystalline modifications with distinct electrical properties.

Findings

Phase B exhibits in-plane hole mobility of 12 cm²/Vs, comparable to rubrene.

Deep-level trap density measured as low as 10^15 cm^-3 eV^-1.

Exponential band tail with a characteristic energy of 22 meV observed.

Abstract

We have synthesized, crystallized and studied the structural and electric transport properties of organic molecular crystals based on a rubrene derivative with {\em t}-butyl sidegroups at the 5,11 positions. Two crystalline modifications are observed: one (A) distinct from that of rubrene with larger spacings between the naphtacene backbones, the other (B) with a in-plane structure presumably very similar compared to rubrene. The electric transport properties reflect the different structures: in the latter phase (B) the in-plane hole mobility of 12 cm$^2$/Vs measured on single crystal FETs is just as high as in rubrene crystals, while in the A phase no field-effect could be measured. The high crystal quality, studied in detail for B, reflects itself in the density of gap states: The deep-level trap density as low as $10^{15}$ cm$^{-3}$ eV$^{-1}$ has been measured, and an exponential band tail with a characteristic energy of 22 meV is observed. The bulk mobility perpendicular to the molecular planes is estimated to be of order of $10^{-3}$ -- $10^{-1}$ cm$^2$/Vs.