Applied Surface Science 258 (2012) 5259–5264 Contents lists available at SciVerse ScienceDirect Applied Surface Science j our nal ho me p age: www.elsevier.com/loc ate/apsusc A comparative study on TiO 2 doped hybrid solar cells Teoman Özdal ∗ , Yakup Hames ¸ , Erdem Aslan Department of Electrical and Electronics Engineering, Mustafa Kemal University, 31200 Hatay, Turkey a r t i c l e i n f o Article history: Received 20 December 2011 Received in revised form 2 February 2012 Accepted 5 February 2012 Available online 13 February 2012 Keywords: TiO2 P3HT Hybrid Solar cell Morphology a b s t r a c t In this study, n-type titanium (IV) oxide (TiO 2 ) and p-type poly (3-hexylthiophene-2,5-diyl) (P3HT) struc- tured various photovoltaic (PV) devices have been produced onto indium tin oxide (ITO) coated glass substrates. For the economy and simplicity, spin coating and doctor blading deposition methods were used in normal atmospheric conditions. The effect of the device morphology on the efficiency of the solar cells was investigated by applying various morphologies such as classic and optimized p–n junc- tions, bulk heterojunction (BHJ) and sandwich structures, respectively. Electrical characterizations of the devices were obtained under AM 1.5 G (100 mW/cm 2 ) solar illumination. © 2012 Elsevier B.V. All rights reserved. 1. Introduction In recent years, metal-oxide semiconductors which are alter- native to the silicons, have been used in many of the inorganic and hybrid solar cell device structures. In particular, the trans- parent metal-oxide semiconductors and nanoparticles are used in organic photovoltaic (OPV) and opto-electronic applications. However, high efficiency OPV devices were prepared in laboratory conditions, in terms of both material and high-tech manufactur- ing process are still relatively complex and expensive [1]. Without using expensive manufacturing technologies, efficient and large area polymer solar cell production will be a significant improve- ment against silicon alternatives. In a recent study on this subject, the authors showed that the low cost manufacturing processes for polymer solar cells and described how compact polymer solar cell modules can be prepared using full roll-to-roll processing with implementation as a sub-component in a flexible electronic prod- uct [2,3]. In this context, polymer solar cell technology can traverse the learning curve in terms of energy payback time and present shorter energy payback times through development according to directions arrived at through life cycle assessments, even when the efficiency is poorer [4]. Some promising studies on alternative environmentally friendly processes and processing materials were also applied. In these studies, aqueous processing of low-band- gap polymers which lower the embedded energy and the process energy, is used. This is also a necessary method for lowering the ∗ Corresponding author. E-mail address: teomanozdal@hotmail.com (T. Özdal). energy payback time for a OPV device [5,6]. In addition, alterna- tive printed metal back electrode applications which are avoiding slow/cumbersome vacuum step in the manufacturing process, fur- ther reduces the total production time and costs of the devices [7]. As a transparent and n-type semiconductor, TiO 2 is a promis- ing metal-oxide for PV and opto-electronic applications [8,9]. In addition, titanium is the ninth most abundant element in the Earth’s crust and the anatase form of the TiO 2 can be easily produced by using low temperature techniques [10]. Also, TiO 2 thin films can easily be produced by low cost production meth- ods such as spin coating [11], electrochemical deposition (ECD) [12] and doctor blading [13]. Due to all these features, TiO 2 still attracts researcher’s attention as a feasible PV material. After the studies [14,15] on nanocrystal TiO 2 electrodes which were sen- sitized by organic dye, interest in the TiO 2 -based inorganic and hybrid solar cells has increased. In subsequent studies, hole con- ductor liquid electrolyte [16,17] and polymer [18,19] materials have been studied successfully. But despite all these develop- ments, the efficiencies of the TiO 2 -based solar cells are very low compared to other alternatives. Especially, bilayered solar cell structures which are made up of by n-TiO 2 electrodes and p-type active layers, have low power conversion efficiencies com- pared to dye-sensitized and BHJ structured alternatives [20–22]. To overcome the low efficiency problem, researchers have stud- ied different solar cell morphologies. In one of these studies, TiO 2 nanoparticle (TiO 2 -np) doped BHJ structured PV devices were prepared with two different polymers which are poly[2-methoxy- 5-(3 ′ ,7 ′ -dimethyloctyl)-p-phenylene vinylene] (MDMO-PPV) and poly(3-octyl thiophene) (P3OT) [23]. In other studies, to investigate 0169-4332/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2012.02.009