Effect of PEDOT:PSS–molecule interface on the charge transport characteristics of the large-area molecular electronic junctions Gunuk Wang a , Seok-In Na b , Tae-Wook Kim b , Yonghun Kim a , Sungjun Park a , Takhee Lee c,⇑ a School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712, Republic of Korea b Institute of Advanced Composite Materials, Korea Institute of Science and Technology, Jeollabuk-do 565-902, Republic of Korea c Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Republic of Korea article info Article history: Received 6 December 2011 Received in revised form 27 January 2012 Accepted 2 February 2012 Available online 18 February 2012 Keywords: Molecular electronic devices Molecular interface PEDOT:PSS abstract We have studied the effect of the PEDOT:PSS–molecule contact on the electrical character- istics of molecular junctions consisting of N-alkanedithiol and naphthalenethiol molecules. In this study, we experimentally investigated the properties of PEDOT:PSS-interlayer molecular junctions as they depended on the two kinds of PEDOT:PSS films (the pure PED- OT:PSS film and the dimethyl sulfoxide (DMSO)-modified PEDOT:PSS film) and their ther- mal annealing treatment. We observed that the electrical properties of these molecular junctions are influenced by the morphology and conductivity of the PEDOT:PSS films and by the thermal treatment. In particular, the resistance of the PEDOT:PSS-interlayer molec- ular junctions depended on the kind of PEDOT:PSS film and the temperature, within the range of elevated temperatures (higher than room temperature) tested. These experimen- tal results are explained by the change of the interfacial properties of the PEDOT:PSS–mol- ecule contact, which are influenced by the morphology change of the PEDOT:PSS film and the removal of residual DMSO or water from the interface. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Molecular electronics have attracted attention in both the scientific and industrial communities because they of- fer a promising route to the miniaturization of future elec- tronic devices [1–6]. Over the past decade, considerable progress has been made in experimental methods for the study of the intrinsic charge transport characteristics through molecular layers in metal–molecule–metal junc- tions [7–13], and reproducible molecular electronic de- vices have been realized [8,10–13]. In particular, device fabrication using the conductive polymer PEDOT:PSS (poly-(3,4-ethylenedioxythiophene) stabilized with poly- (4-styrenesulphonic acid)) as a protecting interlayer be- tween the top metal (typically Au) electrode and the self- assembled monolayer (SAM) molecules has been the sub- ject of increased attention as a platform for stable solid- state molecular devices [8,14]. The technique based on these PEDOT:PSS-interlayer molecular junctions has sev- eral advantages. In particular, it produces reliable and reproducible molecular junctions with a very high device yield (>90%). For this reason, PEDOT:PSS-interlayer molec- ular junctions have been used to successfully investigate the electronic transport properties of various molecules, such as alkyl [8,14,15] and conjugated molecules [15,16]. In addition, specific electronic functionalities, such as memory [17] and photo-switching [18] have also been demonstrated with this method. In comparison to these experimental achievements, how- ever, few efforts have been made to understand the interface properties of the PEDOT:PSS–molecule contact in this junc- tion technique. In fact, it is expected that the interface prop- erty of the PEDOT:PSS–molecule contact is one of the most important factors that needs to be studied to understand the charge transport characteristics of these junctions. There are several distinct features in the PEDOT:PSS-interlayer molecular junction. The resistance of the PEDOT:PSS- 1566-1199/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.orgel.2012.02.002 ⇑ Corresponding author. Tel.: +82 2 880 4269; fax: +82 2 884 3002. E-mail address: tlee@snu.ac.kr (T. Lee). Organic Electronics 13 (2012) 771–777 Contents lists available at SciVerse ScienceDirect Organic Electronics journal homepage: www.elsevier.com/locate/orgel