Synthetic Metals 162 (2012) 268–275 Contents lists available at SciVerse ScienceDirect Synthetic Metals j o ur nal homep ag e: www.elsevier.com/locate/synmet Effect of self-assembly supramolecules on the electrical properties of polyaniline based hole transport layer Tae Hwan Lim a , Kyung Wha Oh b,∗,1 , Seong Hun Kim a,∗∗,1 a Department of Organic and Nano Engineering, Hanyang University, Sungdong-Gu, Seoul 133-791, Republic of Korea b Department of Home Economics Education, Chung-Ang University, Dongjak-Gu, Seoul 156-756, Republic of Korea a r t i c l e i n f o Article history: Received 27 September 2011 Received in revised form 30 November 2011 Accepted 1 December 2011 Available online 11 January 2012 Keywords: Organic solar cells Polyaniline Self assembly Conductivity Water solubility a b s t r a c t To increase the power conversion efficiency of organic solar cells (OSCs), polyaniline (PANI) based film was introduced to the hole transport layer (HTL) of OSCs in this study. Two steps were applied to obtain high conductivity and water solubility of PANI. First, self-assembly supramolecules (SAS) were blended with PANI to improve crystallinity. Second, poly(styrenesulfonic acid) (PSSA), hydrophilic polymer, was grafted on the PANI surface to improve dispersion in aqueous solutions and to increase the conductivity of PANI through a self-doping system. As a result, the conductivity of PANI based film (PANI/SAS16-gr-PSSA) could be improved and reached to 0.81 S/cm in a nano layer state, since this innovative method prevents the polymer chains from the recoiling of PANI. The conductivity of PANI/SAS16-gr-PSSA is higher than that of poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (0.01 S/cm) and PANI-gr-PSSA (0.17 S/cm). The energy level of the prepared PANI/SAS16-gr-PSSA nano layer is approximately 4.83 eV, indicating that it is suitable for a hole transport layer between the ITO electrode and photoactive layer. The OSCs device made of PANI based HTL prepared in this study shows a high power conversion efficiency of approximately 3.4%, which is higher than that of OSCs with PEDOT:PSS (2.8%) and PANI-gr-PSSA (3.0%) layer. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Although the efficiency of OSCs is lower than those of sili- con based solar cells and dye sensitized solar cells (DSSCs), it has various advantages such as cost efficiency, easy fabrication process, and a variety of photovoltaic applications [1–3]. The pho- toactive layer of OSCs is an organized bulk heterojunction (BHJ) structure with its layer composed of a combination of poly(3- hexylthiophene) (P3HT) and [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM) as an electron donor and acceptor. The efficien- cies of OSCs has been remarkably boosted up to approximately 4–5% with the thermal annealing, solvent evaporation control, and insertion of hole injection layer [4–6]. Recently, the efficiency of OSCs has increased to 7.9% under the standard Air Mass (AM) 1.5 Global filter solar condition (1.5G) by controlling HOMO–LUMO energy levels of a photoactive layer. Most OSCs devices utilize indium tin oxide (ITO) as an anode material that has high con- ductivity and transmittance on a rigid substrate. Poly(3,4-ethylene ∗ Corresponding author. Tel.: +82 2 820 5381; fax: +82 2 826 4243. ∗∗ Corresponding author. Tel.: +82 2 2220 0496; fax: +82 2 2281 2737. E-mail addresses: kwhaoh@cau.ac.kr (K.W. Oh), kimsh@hanyang.ac.kr (S.H. Kim). 1 These authors contributed equally to this work. dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was used as a hole transport layer (HTL) between the ITO and photoactive layer to enhance the power conversion efficiency, smoothing the ITO surface, and lowering the work function of the anode [7,8]. The efficiency of OSCs applied PEDOT:PSS as a HTL has increased remarkably; however, various problems have been noticed [9,10]. Most of all, the large particle size of PEDOT induced the degradation of the layer because the aggregate of particles caused defects. The high costs and low electrical conductivity deterred us from using it as a HTL; in addition, its acidity caused the degradation of the OSC device. For these reasons, it is necessary to develop new hole transport material providing better efficiency and longer stability than PEDOT:PSS. Polyaniline (PANI) was selected to the substitute material in our study because of its low cost and high stability [11,12]. PANI could be prepared to have a high molecular weight and electric conductiv- ity by the self-stabilized dispersion polymerization (SSDP) method [13,14]. To adapt PANI as a HTL in OSCs, it needed to be completely soluble in water and have a high conductivity in a thin film state. Two steps were applied in this study to obtain water-soluble prop- erties and a high conductivity. First, self-assembly supramolecules were blended with PANI to improve crystallinity by inducing the orientation of PANI. Because self-assembly supramolecules have a high crystallinity and induce the orientation of PANI chains 0379-6779/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2011.12.002