Materials Science and Engineering B 152 (2008) 105–108 Contents lists available at ScienceDirect Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb Soluble substituted phthalocyanines for OFET applications G. Chaidogiannos a , F. Petraki b , N. Glezos a,∗ , S. Kennou b , S. Neˇ sp ˚ urek c a Institute of Microelectronics, NCSR Demokritos, 15310 Aghia Paraskevi, Attiki, Greece b Department of Chemical Engineering, University of Patras and FORTH/ICE-HT, Gr-26504 Rion, Patras, Greece c Institute of Macromolecular Chemistry, AV-CR, v. v. i. 16206, Prague 6, Czech Republic article info Keywords: Organic electronic transistors Phthalocyanines abstract We compare the performance of organic transistors based on sodium salts of sulfonated metal phthalocya- nines (MePCS x s) to those based on their non-sulfonated counterparts (MePCs). The cases of Me Co, Al are discussed. MePCS x s are water soluble, and therefore can be applied by spin coating, compared to MePCs which require vacuum evaporation. Furthermore they present much higher field mobilities and require much lower operating voltages (V SD < 1 V and V G < 10 V). This feature is due to the presence of the Na + counter ions, a situation similar to organic transistors with electrolyte dielectrics. The current–voltage characteristics depend strongly upon the degree of sulfonation, which has to be controlled in order to optimise device performance. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The interest about organic electronics continuously grows, since they present a good perspective for microelectronic applications that are either not covered by conventional silicon semiconductor technology, or may be manufactured at a decreased cost compared to conventional devices. They usually address to sensors, electronic paper, memory devices, organic light-emitting diodes, solar cells and integrated optoelectronic devices [1–4]. In such applications, one of the critical parameters is the field-effect carrier mobility, which remains smaller than that of silicon transistors. Although molecular materials with the field-effect carrier mobility as high as 1 cm 2 /V s have been reported [5], they present processing diffi- culties due to their limited solubility. The same problem remains with metal phthalocyanines (MePCs), which represent another class of materials that has been investigated for the same purpose [6–8]. They have the advantage of chemical and thermal stability, with charge mobilities in transistor structures up to 0.11cm 2 /V s [9]. An alternative solution, overwhelming the obstacle of the evap- oration in order to fabricate a device, is the class of sodium salts of sulfonated metal phthalocyanines (MePCS x s). They present enhanced solubility compared to their non-sulfonated counter- parts and may stand as candidates for p-type channels in organic transistors. MePCS x s were synthesized (Me Co or Al) and were compared to insoluble MePCs. Our final aim is to develop a ∗ Corresponding author. Tel.: +30 2106503236; fax: +30 2106511723. E-mail address: glezos@imel.demokritos.gr (N. Glezos). device that combines an easy film preparation process with opti- mal performance. Some preliminary tests were run on Al(OH)- PC(SO 3 Na) x , x = 1–4, based transistors [10], showing promising behaviour. Whereas MePC based OFETs were fabricated by vacuum evapo- ration in high vacuum, MePCS x based OFETs were prepared by spin coating at room temperature. The charge mobilities arising were much higher. 2. Experimental 2.1. Materials Soluble phthalocyanines were all synthesized from non- substituted ones [11]. They were sulfonated during heating in an oil bath, equipped with reflux cooler, agitator, thermometer and dosing funnel. Fuming sulfuric acid was charged into the flask and subsequently the MePC was gradually charged through the dos- ing funnel into the agitated fuming sulfuric acid. The mixture was agitated until all MePC was fully dissolved. Afterwards, the dosing funnel was replaced by an inlet of nitrogen, to allow the sulfonation process to be carried out under a nitrogen blanket. The reaction mixture was agitated and heated up to high temperature (over 100 ◦ C) and subsequently kept for 30 min at the adjusted tempera- ture. The concentration of fuming sulfuric acid and the temperature of the sulfonation were chosen according to the target level of the sulfonation. The number of substituents depends on the oleum con- centration, temperature and duration of the reaction. An analysis on the sulfonation of the sodium salt of sulfonated hydroxyalu- minium phthalocyanine [Al(OH)PC(SO 3 Na) x ], x = 1–4, synthesized 0921-5107/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2008.06.025