ORIGINAL PAPER Prakash R. Somani Æ S. Radhakrishnan Solid state electrochemical reaction in photocells made using conducting polyaniline and sensitized with methylene blue Received: 2 April 2002 / Accepted: 9 July 2002 / Published online: 11 September 2002 Ó Springer-Verlag 2002 Abstract The effect of small concentration of methylene blue (MB) on photocurrents was studied in solid state photoelectrochemical cells fabricated using conducting polyaniline (PANI) coated electrodes sandwiched with a solid polymer electrolyte, viz. poly(vinyl alcohol) (PVA) with phosphoric acid. These exhibit good photoresponse to visible light (maximum photosensitivity factor of the order of 10). The current-voltage (I-V) characteristics in such cells reveal that the charge transport is ohmic. Also, an electrochemical reaction (motion of Cl – from SPE+MB to PANI) is observed at 1.2–1.3 V, which gives rise to a sudden increase of current at this parti- cular voltage. The presence of illumination enhances this electrochemical reaction. The combined effect, i.e. ohmic charge transport and an electrochemical reaction, is observed in the I-V characteristics. Along with the dye concentration, the photosensitivity is observed to be field/voltage dependent. The sensitization effects are due to lowering of the potential barrier formed at the PANI/ SPE+MB interface under illumination. Keywords Dye sensitization Æ Solid state electrochemical cells Æ Solid polymer electrolyte Æ Conducting polymers Æ Polyaniline Introduction Conducting polymers are finding increasing numbers of applications in various electronic devices such as elec- trochromic displays (ECD), light emitting diodes (LED), chemical sensors, etc. [1, 2, 3, 4, 5, 6, 7, 8, 9]. Like photovoltaic devices, the devices which are useful for photoenergy conversion are photoelectrochemical (PEC) cells, which showed promising results but could not be used for practical applications owing to some drawbacks [10, 11]. One of the major drawbacks for such cells has been the liquid electrolyte component, which makes it difficult to fabricate in large areas. Some attempts have been made in the past for replacement of the liquid electrolyte with a solid polymer electrolyte [12, 13]. However, these authors have used conventional inor- ganic semiconductors such as TiO 2 , ZnO, etc., for the active photoelectrode, which, again, does not ease the method of processing. Another drawback of these cells has been the very low photocurrents obtained owing to the cell resistance and/or low photosensitivity of the material. The photosensitivity of such materials can be enhanced (and/or extended into the visible region) by the use of dyes and pigments. We made attempts in the past to fabricate PEC cells using simultaneously conducting polymers and solid polymer electrolytes [14, 15, 16]. We report here our studies on such photocells made using conducting polyaniline (PANI) and sensitized with methylene blue (MB) dye. Studies were also done in order to understand the charge transport mechanism in such cells. Charge transport is mainly ohmic in nature. A solid state electrochemical reaction is also observed to occur in the photocells under the present investigations. Experimental The photocells were fabricated by the following method. First, thin gold films were deposited on clean microscopic grade glass sub- strates. Conducting PANI films were deposited on these by stan- dard potentiostatic technique [17] using a single-compartment J Solid State Electrochem (2003) 7: 166–170 DOI 10.1007/s10008-002-0308-1 P.R. Somani (&) Photonics and Advanced Materials Laboratory, Centre for Materials for Electronics Technology (C-MET), Panchawati, Off Pashan Road, Pune 411 008, India E-mail: psomani_cmetp@yahoo.com E-mail: psomani1@yahoo.com Tel.: +91-02424-22620 S. Radhakrishnan Polymer Science and Chemical Engineering, National Chemical Laboratory (NCL), Pashan Road, Pune 411 008, India P.R. Somani Near Agasti Theatre, At.-Po.-Tal.-Akole, Dist. A. Nagar, Via Sangamner, Akole 422601, Maharashtra, India