Supporting Information

Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2014.
Supporting Information
for Adv. Funct. Mater., DOI: 10.1002/adfm.201400877
Interface Functionalities in Multilayer Stack Organic Light
Emitting Transistors (OLETs)
Raffaella Capelli,* Franco Dinelli, Massimo Gazzano,
Riccardo D’Alpaos, Andrea Stefani, Gianluca Generali,
Mauro Riva, Monica Montecchi, Angelo Giglia, and Luca
Pasquali
Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2013.
Supporting Information
Interface Functionalities in Multilayer Stack Organic Light Emitting Transistors (OLETs)
R. Capelli1*, F. Dinelli2, M. Gazzano3, R. D’Alpaos4, A. Stefani4, G. Generali4, V. Biondo4 M.
Riva5, M. Montecchi1,6, A. Giglia1, L. Pasquali1,6,7
1
CNR - Istituto Officina dei Materiali, S.S. 14, km 163.5 in Area Science Park, I-34012 Trieste,
Italy. E-mail: [email protected]
2
CNR- Istituto Nazionale di Ottica, Area della ricerca di Pisa - Via G. Moruzzi,1 Località S.
Cataldo - 56124 Pisa, Italy
3 CNR - Istituto per la Sintesi Organica e la Fotoreattività, via P. Gobetti 101, 40129 Bologna, Italy
4
ETC S.r.l. – Via P. Gobetti 101 – 40129 Bologna, Italy 5
SAES Getters S.P.A. – Viale Italia 77 – 20020 Lainate (MI), Italy 6
Dipartimento di Ingegneria ‘Enzo Ferrari’, Università di Modena e Reggio Emilia, Via Vignolese
905, 41125 Modena, Italy
7
Department of Physics, University of Johannesburg, PO Box 524, Auckland Park, 2006, South
Africa
In order to check the generality of the field-effect transport degradation that we observe in DH4T
semiconducting films, when used within a vertical organic heterojunction, we have fabricated and
characterized different small molecule bi-layer structures. Each bi-layer being formed by a first
amorphous polycrystalline film and a second top semiconducting layer made with molecules, in
particular, showing high field-effect transport properties when used as active region of single layer
Organic Thin Film Transistors (OTFTs). In all the studied bi-layer configurations we have observed
a severe degradation of the top semiconducting layer transport properties with respect to the single
layer thin film transistor configuration. Here we report in particular the results relative to the
Alq3/Pentacene bi-layer. Pentacene is one of the most consolidated p-type semiconductor with high
field-effect mobility values when used in single layer OTFT configuration.
In order to exclude an active role of Alq3 on the electrical behaviour of the considered bi-layer
configurations, we have fabricated transistors based on a 30 nm thick Alq3 film only. Specifically,
we report the p-type multiple output characteristics (Figure S1a) and the p-type transfer curve
(Figure S1b). The same device geometry reported in the experimental section of the main
manuscript has been used. No gate modulation can be observed. However a bulk charge transport is
evidenced by the electrical characterization of the device, compatible with the fact that Alq3 is
commonly used as electron transport layer (ETL) in Organic Light Emitting Diodes (OLEDs) with a
bulk mobility of the order of 10-6 cm2/Vs.
The electrical characteristics of single layer OTFTs based on Pentacene are reported in Figure S2.
The mobility extracted from the locus curve of Figure S2a is of about 0.22 cm2/Vs. In Figures S3
are reported the electrical characteristics of Pentacene film grown on top of Alq3. The mobility
value is calculated from the locus curves of Figures S3a. As for the case of the Alq3/DH4T bilayer, Pentacene transport properties result clearly degraded with respect to the single layer OTFT
cases. This represents further evidence of the impact of the bottom amorphous layer on the
field-effect properties of the top layer.
Most trends observed for the DH4T/Alq3 system and discussed in the paper, are recognizable also
in the bi-layer structure of Figure S3. Features indicating bad charge injection are clearly present in
the reported transfer curves (Figures S3c, S3d), and the mobility results degraded by more than two
orders of magnitude with respect to the PMMA/Pentacene configuration shown in Figure S2. We
conclude that DH4T/Alq3 interface can be considered as a prototypical example representing a
larger class of organic/organic interfaces. In particular, all the interfaces are based on a
semiconducting film with crystalline and oriented domains grown on top of a polycrystalline
amorphous film, both the organic films being constituted by conjugated molecular systems.
Figure S1. Electrical characteristic of a thin film transistor based on Alq3 molecules.
Figure S2. Electrical characteristic of a thin film transistor based on Pentacene molecules.
Figure S3. Electrical characteristics and HOMO-LUMO levels distribution of a thin film
transistor based on Alq3/Pentacene bi-layer.