1 Graphene controlled organic photodetectors 2 A. Mekki a Q1 , A. Dere b , Kwadwo Mensah-Darkwa c , Ahmed Al-Ghamdi d , R.K. Gupta e, **, 3 K. Harrabi a , W.A. Farooq f , Farid El-Tantawy g,h , F. Yakuphanoglu a,d, * 4 a Department of Physics, King Fahd University of Petroleum & Minerals Dhahran, 31261, Saudi Arabia 5 b Department of Physics, Faculty of Science, Fırat University, Elazig, Turkey 6 c Department of Materials Engineering, College of Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana 7 d Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia 8 e Department of Chemistry, Pittsburg State University, Pittsburg, KS 66762, USA 9 f Department of Physics and Astronomy, College of Science, King Saud University, Riyadh, Saudi Arabia 10 g Nanoscience and Nanotechnology Laboratory, Firat University, Elazı g, Turkey 11 h Department of Physics, Faculty of Science, Suez Canal University, Ismailia, Egypt A R T I C L E I N F O Article history: Received 12 February 2016 Received in revised form 6 March 2016 Accepted 11 March 2016 Available online xxx Keywords: Solar energy materials Photodiode Graphene oxide Methylene blue A B S T R A C T Drop casting deposition technique was used to fabricate graphene oxide doped methylene blue (GO doped MB) photodiode, Al/p-Si/GO doped MB/Au. The effects of illumination on the current–voltage (I–V) characteristics of the Al/p-Si/GO doped MB/Au Schottky diode for optical sensing applications were explored. The reverse current of the diode in the reverse bias increases with the increasing illumination intensities. The obtained trends for both ideality factor and barrier height are in agreement, suggesting that they are both affected by GO doping. The photosensitivity of the photodiodes was investigated. The highest photosensitivity was observed for the diode having 0.03 GO:MB ratio with I photo /I dark ratio of 8.67  10 3 at 100 mW/cm 2 under 10 V. The rectification ratio was of the order of 10 4 . In addition, the capacitance–voltage (C–V) and conductance–voltage (G–V) measurements of the diode were studied in the frequency range of 10 kHz–1 MHz. The measured values of the capacitance decrease with the increasing frequency. The decrease in capacitance was explained on the basis of interface states. The photoelectrical properties of Al/p-Si/GO doped MB/Au devices indicate that the prepared diodes can be used both as a photodiode and a photocapacitor in optoelectronic device applications. ã 2016 Published by Elsevier B.V. 12 1. Introduction 13 The graphite family is well researched material because of its 14 inherent electrical, chemical and mechanical properties, along 15 with its several practical applications [1]. Lots of attention has been 16 given to the exploration of the properties of graphite such as 17 graphene, graphene oxide (GO) and reduced graphene oxide 18 (RGO), for several applications [2–4]. Graphene was discovered by 19 mechanical exfoliation method [5], is a one-atom thick layer of 20 graphite. Many researchers have explored the new world of 21 graphene due to its unique and remarkable electronic properties 22 [6–8], such as high carrier mobility, micron scale mean free path 23 and high saturation velocity [9]. Q4 24 Numerous reports have pointed to extensive applications and 25 proposed applications of graphene [2,10–13]. Other reported 26 literature have shown the use of graphene in the development 27 of solar cells and diodes [14,15]. Li et al. [14] used highly conductive 28 semitransparent graphene sheets combined with an n-type silicon 29 wafer to fabricate solar cells with power conversion efficiencies up 30 to 1.5% at AM 1.5 and an illumination intensity of 100 mW cm 2 . Lv 31 et al. [16] have used soluble graphene oxide to fabricate graphene 32 films to measure their time-resolved photoconductivity, they 33 observed higher photoconductivity with higher photon energy at 34 same incident light intensity. Xia et al. [10] also used graphene to 35 fabricate photodetectors, and suggested that the generation and 36 transport of photo-carriers in graphene differ fundamentally from 37 those in photodetectors made from conventional semiconductors 38 because of the unique photonic and electronic properties of the 39 graphene. They also demonstrated that the photo response of 40 ultrafast transistor-based photodetectors made from single- and 41 few-layer grapheme does not degrade for optical intensity 42 modulations up to 40 GHz. * Corresponding author at: Q2 King Fahd University of Petroleum & Minerals Dhahran, Department of Physics, Elazig 31261, Turkey. ** Corresponding Q3 author. E-mail addresses: ramguptamsu@gmail.com (R.K. Gupta), fyhanoglu@firat.edu.tr (F. Yakuphanoglu). http://dx.doi.org/10.1016/j.synthmet.2016.03.015 0379-6779/ ã 2016 Published by Elsevier B.V. Synthetic Metals xxx (2015) xxx–xxx G Model SYNMET 15264 1–14 Please cite this article in press as: A. Mekki, et al., Graphene controlled organic photodetectors, Synthetic Met. (2016), http://dx.doi.org/ 10.1016/j.synthmet.2016.03.015 Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/sy nmet