# Flexible n‑Channel Organic Transistors with Low Contact Resistance

## TL;DR

This paper presents new organic transistors with low contact resistance, suitable for both rigid and flexible electronics.

## Contribution

The study introduces a novel method to reduce contact resistance in n-channel organic transistors using thiols like MeSTP.

## Key findings

- PhC2-BQQDI transistors with MeSTP-functionalized contacts achieved contact resistances as low as 130 Ω cm on silicon and 210 Ω cm on flexible substrates.
- Transistors on flexible substrates showed excellent bending stability.
- MeSTP functionalization minimized contact resistance due to its low effective work function.

## Abstract

Three promising small-molecule organic semiconductors,
namely,
2,9-bis­(heptafluoropropyl)-4,7,11,14-tetrabromo-1,3,8,10-tetraazaperopyrene
(TAPP-Br4), N,N′-bis­(2,2,3,3,4,4,4-fluorobutyl)-(1,7
and 1,6)-dicyano-perylene-tetracarboxylic diimide (ActivInk N1100),
and diphenylethyl-3,4,9,10-benzo­[de]­isoquinolino­[1,8-gh]­quinolinetetracarboxylic diimide (PhC2-BQQDI),
are employed for the fabrication of n-channel thin-film
transistors (TFTs). The TFTs are fabricated on rigid silicon and flexible
polymeric substrates, in both the inverted staggered (bottom-gate,
top-contact) and the inverted coplanar (bottom-gate, bottom-contact)
device architecture. In the coplanar TFTs, the source and drain contacts
are functionalized with one of four different thiols to minimize contact
resistance. The best performance is obtained for PhC2-BQQDI
TFTs with bottom contacts functionalized using 4-(methylsulfanyl)-thiophenol
(MeSTP). For these TFTs, we measure contact resistances of 130 Ω
cm for TFTs fabricated on silicon substrates and 210 Ω cm for
TFTs on flexible polymeric substrates; these are the smallest contact
resistances reported to date for n-channel organic
TFTs, despite the fact that the measurements are carried out in ambient
air. The observation that functionalizing the contacts with MeSTP
leads to the smallest contact resistance is consistent with the fact
that MeSTP provides the lowest effective work function. The TFTs fabricated
on flexible polymeric substrates showed excellent bending stability.