Effects of Chemical Modification of Indium-Tin-Oxide with Benzene Derivates on the Performance of Organic Photovoltaic C
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Effects of Chemical Modification of Indium-Tin-Oxide with Benzene Derivates on the Performance of Organic Photovoltaic Cells of ITO/CuPc/C60/BCP/Al Khayankhyarvaa Sarangerel1, Altantsetseg Delgerjargal2, Byambasuren Delgertsetseg2, and Chimed Ganzorig2 1
Department of Electronics and Computer, School of Power Engineering, Mongolian University of Science and Technology, Ulaanbaatar, Mongolia 2
Center for Nanoscience and Nanotechnology and Department of Chemical Technology, School of Chemistry and Chemical Engineering, National University of Mongolia, Ulaanbaatar, Mongolia ABSTRACT Organic thin film photovoltaic (PV) cells have attracted attention because of their ease of fabrication and potential for low cost production. In this paper, we study the effects of chemical modification of indium-tin-oxide (ITO) on the performance of organic PV cells. The organic PV cells are fabricated, with the cell configuration of ITO/copper phthalocyanine (CuPc) (20 nm)/fullerene (C60) (40 nm)/Al with and without bathocuproine (BCP) (10 nm) between C60 and Al. By the use of para-substituted benzenesulfonyl chlorides with different terminal groups of Hand Cl-, the energy offset at the ITO/CuPc interface is tuned widely depending upon the interface dipoles and thus the correlation between the change in the ITO work function and the performance of the PV cells by chemical modification is examined. INTRODUCTION Formation of monolayers by self-assembly at electrode surfaces has been widely used in recent years. How to bind molecules on electrode surfaces has been studied extensively among electrochemists since mid-1970s and is called chemical modification of electrode surfaces [1,2]. Studies for formation of various organic monolayers on various transparent oxide electrode (TCO) surfaces were reviewed in Ref. [3]. The ITO is the most widely used as a transparent electrode in organic photovoltaic (PV) cells [4] due to its high conductivity, work function, and transparency in the visible spectral range. However, the work function of ITO is generally not sufficiently large for the contact to be ohmic and so there is a barrier to charge injection. Thus, various surface treatments of ITO have been attempted to change the work function of ITO in order to control the charge injection barrier height reviewed in Ref. [5]. Fujihira and coworkers [6] carried out pioneering work on covalently attaching organic molecules with functional groups such as -COOH and -COCl onto SnO2 surface. The latter was more reactive [6]. Wrighton and coworkers [7] took advantage of the selective surface attachment of carboxylic or phosphonic acid to ITO electrode and thiol to Au electrode. By the use of acid chlorides [8,9], ITO surfaces were modified quickly and the fine and wide change in ITO work function was realized. For enhancing device performance of organic PV cells, increase of the work function of ITO surfaces have been attempted by self-assembled monolayers
(SAMs) [8,10-14]. Among them, we have demonstrated tuning the work function by chemical modification
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