Structural, morphological, electrical and electron transport studies in ZnO–rGO (wt% 5 0.01, 0.05 and 0.1) based dye-sensitized solar cell H. Abdullah • Noor Aishah Atiqah • A. Omar • Izamarlina Asshaari • Savisha Mahalingam • Zikri Razali • Sahbudin Shaari • J. S. Mandeep • Halina Misran Received: 27 September 2014 / Accepted: 20 November 2014 Ó Springer Science+Business Media New York 2015 Abstract Zinc oxide–reduced graphene oxide (ZnO–rGO) thin films were fabricated on a fluorine-doped tin oxide glass substrate by a chemical bath deposition method. The thin films were immersed in the Eosin Y dye for 24 and 48 h to be fabricated as a dye-sensitized solar cell. ZnO hexagonal wurtzite structures were analyzed by X-ray diffraction ana- lysis. Field effect scanning electron microscope showed the images of ZnO nanoparticles and nanobranches. The atomic force microscopy analysis estimated the average roughness of ZnO–rGO films doped with 0.01, 0.05 and 0.1 wt% which varied from 178 to 267 nm. The electrical or photo- voltaic performance of ZnO–rGO were measured and compared accordingly by considering their power conver- sion efficiency, g, photocurrent density, J sc , open-circuit voltage, V oc and fill factor, FF. The cell’s efficiency of ZnO with 0.01 wt% rGO, 0.05 wt% rGO and 0.1 wt% rGO reached g = 2.36, 0.78 and 0.38 %, respectively. EIS ana- lysis estimated the effective electron lifetime, s eff , effective electron chemical diffusion coefficient, D eff , effective elec- tron diffusion length of the photoanode, L n , charge transport resistance, R ct and transport resistance, R t . 1 Introduction A combustion product of fossil fuels includes polluted air, acid rain, and harmful gases. An alternative to implement a clean energy sources or renewable energy allows us to improve the quality of life. Solar cell is one of the alternatives to generate energy or power without producing harmful wastes. Dye- sensitized solar cell (DSSC) is a third generation of solar cell that received great attention in the solar cell technology, research and development. DSSCs are cheaper compare to silicon-based solar cells or any conventional p-n junction solar cells [1, 2]. The main structure of DSSC’s cell consists of five important parts including a conductive glass substrate, a semiconductor film (usually TiO 2 ), a dye (or sensitizer), an electrolyte to provide a redox process and a counter electrode to regenerate the redox mediator [3]. In general, photoanode of the DSSCs are developed from a wide-band gap semicon- ductor oxide films such as TiO 2 , ZnO and Nb 2 O 5 with larger surface area [2, 4]. ZnO and TiO 2 have the same band gap and conduction band energies (3.37 eV) but ZnO possess higher electron mobility compare to TiO 2 [2]. Higher electron mobility influence the power conversion efficiency (PCE) of the ZnO based DSSC. Currently, ZnO-based DSSC exhibited PCE of 5.6 % [5], which is still low compared to TiO 2 - based DSSC [6]. In order to increase the efficiency of ZnO-based DSSC, a combination of ZnO and graphene is proposed in the current work. Firstly discovered by Novoselov in 2004, H. Abdullah (&)  N. A. Atiqah  A. Omar  S. Mahalingam  Z. Razali  J. S. Mandeep Department of Electrical, Electronic and System Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia e-mail: huda@eng.ukm.my I. Asshaari Unit Pengajian Asas Kejuruteraan (UPAK), Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia S. Shaari Photonic Technology Laboratory, Department of Electrical, Electronics and System Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia H. Misran Department of Mechanical Engineering, College of Engineering, Universiti Tenaga Nasional, Jalan IKRAM-UNITEN, 43000 Kajang, Selangor, Malaysia 123 J Mater Sci: Mater Electron DOI 10.1007/s10854-015-2679-y