A latent pigment strategy for robust active layers in solution-processed, complementary organic field-effect transistors

Isis Maqueira-Albo,Giorgio Dell'Erba,Luca Beverina,Mario Caironi,Giorgio Ernesto Bonacchini,Mauro Sassi,Roland Resel,Myles Rooney,Giuseppina Pace

doi:10.1039/c7tc03938g

Abstract

A latent pigment approach enables solution-processing of small molecule films that are insoluble in aggressive solvents upon thermal cleavage of solubilizing groups.

Highlights

Since an optimized electronic device is typically composed of several functional layers that have to be deposited one on top of the other, an obvious requirement is that the deposition of a new layer must not alter the electronic properties of the underlying layers.[21,22,23] One of the most exploited approaches to comply with such a requirement is to rely on orthogonal solvents, i.e. solvents that solubilize the compound being deposited but cannot solubilize the layers below.[24]
We demonstrate the use of tert-butyloxycarbonyl (t-Boc) functionalized diketopyrrolopyrrole and perylene-diimide small molecules for good hole and electron transporting films. t-Boc thermal cleavage leads to densification of the films, along with a strong structural rearrangement of the deprotected molecules, strongly improving charge mobility in both p- and n-type field-effect transistors (FETs)
The thermal cleavage of both T3DPP-t-Boc and PDI-t-Boc was characterized by means of thermogravimetric analysis (TGA)

Summary

Introduction

Since an optimized electronic device is typically composed of several functional layers that have to be deposited one on top of the other, an obvious requirement is that the deposition of a new layer must not alter the electronic properties of the underlying layers.[21,22,23] One of the most exploited approaches to comply with such a requirement is to rely on orthogonal solvents, i.e. solvents that solubilize the compound being deposited but cannot solubilize the layers below.[24]. Mobilities, achieved for thiophenes with a diketopyrrolopyrrole core or quinacridone after the thermal cleavage of the t-Boc groups, were in the order of 10À6 cm[2] VÀ1 sÀ1.27 The latent pigment approach applied to small molecules has never been employed so far neither for the development of top-gate FETs, nor for n-type FETs in general, with the latter path being further complicated by the typical lower environmental stability of organic semiconductors with high electron affinity.[40,41,42] An example of a high electron affinity, t-Boc functionalized small molecule was only reported for a PDI-based latent pigment used in luminescent solar concentrators.[43] In this contribution, we report the use of thermo-cleavable t-Boc functionalized diketopyrrolopyrrole (DPP) and perylenediimide (PDI) small molecules for the preparation of highly insoluble semiconducting layers in solution-processed top-gate FETs, enabling both p- and n-type staggered transistors and paving the way for the possible future use of this strategy in robust complementary circuits. The top dielectrics can be processed from typically forbidden solvents, yielding good performing FETs

Results and discussion

Â 10À5 — 4 Â 10À5

Conclusions