Efficient modification of transparent graphene electrodes by electron beam irradiation for organic solar cells Su-Hyeon Kim a , Yong-Jin Noh a , Sung-Nam Kwon a , Byung-Nam Kim b , Byung-Cheol Lee b , Si-Young Yang a , Chan-Hee Jung c , Seok-In Na a, * a Professional Graduate School of Flexible and Printable Electronics, Polymer Materials Fusion Research Center, Chonbuk National University, 664-14, Deokjin-dong, Deokjin-gu, Jeonju-si 561-756, Jeollabuk-do, Republic of Korea b Radiation Equipment Research Division, Korea Atomic Energy Research Institute, Daedeok-daero 989-111, Yuseong-gu, Daejeon 305-353, Republic of Korea c Research Division for Industry and Environment, Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, Jeongeup-si 580-185, Jeollabuk-do, Republic of Korea Introduction Graphene that is a two dimensional and sp 2 -bonded carbon- atomic monolayer with honeycomb lattice has drawn a signifi- cant attention owing to its outstanding optical transmittance, electrical and thermal conductivity, and mechanical properties, which are highly beneficial for various applications such as transparent electrodes, transistors, nanosensors, and photovol- taics [1–5]. In general, for graphene analyses and graphene-device fabrica- tion, the use of the scanning microscopy, transmission electron microscopy, and electron beam lithography was usually required [6–8]. This electron beam irradiation on graphene can have influence on graphene structure and properties, resulting from lattice defects or oxidation by breaking the carbon bond in graphene [6–10]. However, no detailed studies of the electron- beam effects on graphene under a wide range of electron-beam irradiation have been investigated so far, which could be highly needed for fully understanding the overall structural and electrical properties of graphene. More importantly, it was recently known that the functionalization of graphene by controlling the graphene- surface structure could be highly beneficial for its practical device application as transparent electrodes and charge transporting layers [11,12]. Thus, controlling intrinsic properties of the graphene through irradiation with UV, electron beam, and ion beam has been explored, and its feasibility has been reported [13,14]. However, approaches on the electron-beam based graphene functionalization have hardly been studied, and no researches on practical applications of electron-beam-treated graphene as a transparent electrode in organic solar cells have been studied so far. In this study, the simple, solvent-free, and ambient temperature electron beam (EB)-based modification of graphene for its use as a transparent electrode in organic solar cells (OSCs) was described. The graphene was irradiated under various EB-exposure times to modify its properties. Furthermore, the modified graphene was practically applied as a transparent electrode of OSCs to investigate the effectiveness of the electron-beam-based modification. Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx * Corresponding author. Tel.: +82 63 270 4465; fax: +82 63 270 2341. E-mail addresses: nsi12@jbnu.ac.kr, seokinna@gmail.com (S.-I. Na). A R T I C L E I N F O Article history: Received 17 September 2014 Received in revised form 21 November 2014 Accepted 26 November 2014 Available online xxx Keywords: Organic solar cells Electron beam irradiation Graphene Carbon electrodes Transparent electrodes A B S T R A C T A simple, solvent-free, and efficient electron beam (EB)-irradiation based modification of graphene and its use as a transparent electrode in organic solar cells (OSCs) were described in this research. A chemical vapor deposition (CVD)-prepared graphene was irradiated by an energetic EB for various irradiation times to modify its chemical and electrical properties. The analytical results revealed that the graphene was successfully modified by EB irradiation-induced oxidation and amorphization, and thereby resulting in the increase in its sheet resistance and work function. Moreover, on the basis of the results of the OSC- performance test, the OSCs with the graphene electrode modified at the irradiation time of 5 s exhibited the highest power conversion efficiency of 2.76%, which is much better than that with a non-irradiated graphene electrode. Therefore, it can be confirmed that the EB irradiation could be used in effectively tuning the graphene’s properties and the resulting EB-treated graphene can be directly applicable as a transparent electrode and beneficial for high-performance organic electronics. ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. G Model JIEC-2318; No. of Pages 4 Please cite this article in press as: S.-H. Kim, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.11.031 Contents lists available at ScienceDirect Journal of Industrial and Engineering Chemistry jou r n al h o mep ag e: w ww .elsevier .co m /loc ate/jiec http://dx.doi.org/10.1016/j.jiec.2014.11.031 1226-086X/ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.