Impact of isoelectric points of nanopowders in electrolytes on electrochemical characteristics of dye sensitized solar cells Shyama Prasad Mohanty, Parag Bhargava * Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076, India highlights < Different isoelectric point nanopowders were used for preparation of electrolytes. < Zeta potential measurement confirmed the adsorption of ions on powder surface. < Cations get adsorbed onto the surface of powders having low isoelectric point. < Anions were adsorbed on the surface of high isoelectric point powder. < Electrolyte loaded with high isoelectric point powder shows poor cell performance. article info Article history: Received 4 April 2012 Received in revised form 13 June 2012 Accepted 17 June 2012 Available online 2 July 2012 Keywords: Isoelectric point Zeta potential Adsorption Nanopowder loaded electrolyte Electrochemical Dye sensitized solar cell abstract Nanoparticle loaded quasi solid electrolytes are important from the view point of developing electrolytes for dye sensitized solar cells (DSSCs) having long term stability. The present work shows the influence of isoelectric point of nanopowders in electrolyte on the photoelectrochemical characteristics of DSSCs. Electrolytes with nanopowders of silica, alumina and magnesia which have widely differing isoelectric points are used in the study. Adsorption of ions from the electrolyte on the nanopowder surface, char- acterized by zeta potential measurement, show that cations get adsorbed on silica, alumina surface while anions get adsorbed on magnesia surface. The electrochemical characteristics of nanoparticulate loaded electrolytes are examined through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). DSSCs fabricated using liquid, silica or alumina loaded electrolytes exhibit almost similar perfor- mance. But interestingly, the magnesia loaded electrolyte-based cell show lower short circuit current density (J SC ) and much higher open circuit voltage (V OC ), which is attributed to adsorption of anions. Such anionic adsorption prevents the dark reaction in magnesia loaded electrolyte-based cell and thus, enhances the V OC by almost 100 mV as compared to liquid electrolyte based cell. Also, higher electron life time at the titania/electrolyte interface is observed in magnesia loaded electrolyte-based cell as compared to others. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Dye sensitized solar cells (DSSCs) are low cost photovoltaics which have attained an efficiency of 12.3% in the lab scale [1]. Most of the higher efficiency DSSCs are based on liquid electrolytes. Liquid electrolytes based cells show the tendency of solvent vola- tilization over a period of time. Hence, work is being carried out on development of solid electrolyte or quasi solid electrolytes as substitutes for liquid electrolytes. Typically, solid electrolyte based cells are inferior in performance to those based on liquid electrolyte due to improper filling of mesoporous electrode and poor hole mobility [2,3]. In contrast, quasi solid electrolytes achieve almost similar performance as liquid electrolytes with enhanced longevity of the cell [4e6]. These electrolytes have been prepared using 3-D polymer network or contiguous network of nanopowders to ach- ieve gelation of liquid electrolyte [6]. Thermal energy is required to make a homogeneous mixture and trap the liquid in the entangled polymeric network [4]. Alternatively, initiators are required to chemically form the network from monomer units [7]. Gelation process with the use of nanopowders is much simpler as compared to polymers. Addition of nanopowders, beyond a certain weight fraction to liquid electrolytes leads to gel formation. Several nanopowders such as silica, titania, carbon black and carbon nanotubes have been utilized for the purpose [6,8e10]. In case of silica, titania the cationic part of the iodide salt in the electrolyte * Corresponding author. Tel.: þ91 22 25767628; fax: þ91 22 25726975. E-mail address: pbhargava@iitb.ac.in (P. Bhargava). Contents lists available at SciVerse ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour 0378-7753/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jpowsour.2012.06.080 Journal of Power Sources 218 (2012) 174e180