July 2, 2011 10:42 S1793-6047 00182 fa Functional Materials Letters Vol. 4, No. 2 (2011) 199–203 © World Scientific Publishing Company DOI: 10.1142/S1793604711001828 HETERO-JUNCTION COMPOSED OF POLY(3,4-ETHYLENEDIOXYTHIOPHENE) WITH POLY(STYRENESULPHONATE) AND IODINE DOPED TITANIUM DIOXIDE KATARZYNA SIUZDAK and ANNA LISOWSKA-OLEKSIAK ∗ Gdansk University of Technology, Chemical Faculty Department of Chemical Technology, Narutowicza 11/12 80-233 Gdansk, Poland ∗ alo@pg.gda.pl Received 29 December 2010; Revised 27 April 2011 This work presents new bulk p-n hetero-junction where iodine doped TiO 2 (I-TiO 2 ) acts as n and poly(3,4-ethyle- nedioxythiophene):polystyrenesulphonate (pEDOT:PSS) as p-element. Heterogeneous films were obtained by means of poten- tiostatic polymerization of monomer on the metal electrode in presence of suspended I-TiO 2 particles in the electrolyte, (applied potentials in a range of 0.8–1.1 V vs. Ag/AgCl/0.1 M KCl). The procedure brings about hybrid films where I-TiO 2 particles are uniformly incorporated into the bulk polymer matrix. An incorporation of I-TiO 2 into the pEDOT:PSS matrix causes increase in the measured current under visible light illumination. Keywords: Conducting polymers; iodine doped titanium dioxide; hetero-junction; photocurrent; electrochemistry. Combination of inorganic and organic materials attracts much attention in recent years. 1 These composites where metal oxide serves as inorganic and conducting polymer as organic part are especially investigated because of their promising optoelectronic properties. The hybrid inorganic/organic sys- tems were used in research on their application for ultra- sensitive radiation detection, 2 electrochromic devices, 3 light- emitting diodes 4 and solar cells. 5 In the case of photovoltaic cells, a proposed organic/inorganic junction is the alterna- tive for usually used silicon solar cells. In this field, MnO 2 , Fe 2 O 3 or TiO 6 2 are proposed as a n-element and polyaniline, 7 poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate) 8 or polyazulene 9 are tested as a p-element. In order to combine both organic and inorganic parts, various electrochemical and mechanical methods like potentiostatic deposition, chemical vapour deposition or inkjet printing 10 are used. The pictorial energy diagram for p and n elements in a studied hetero-junction is presented in Fig. 1. The possible mechanism of photon excitation and the motion direction for electrons and holes is shown there. 11-13 In contrast to pure TiO 2 , in iodine doped TiO 2 lower photon excitation energy from the occupied states of the I-O-Ti (a) to unoccupied I-O-Ti (b) is supposed to be responsible for extended light absorbance region ( E g = 2.8 eV) and therefore contribute to an increase in registered photocurrent. 14 Furthermore, according to Tojo et al. 15 in I-TiO 2 the recombination of e - -H + pairs is effec- tively inhibited due to the active I 5+ sites able to reversible electron trapping. These features strongly support an applica- tion of I-TiO 2 in the proposed hetero-junction. Herein we report studies concerning the p-n junction consisted of iodine doped TiO 2 (I-TiO 2 ) and pEDOT:PSS. The proposed hybrid films were potentiostatically deposited from the I-TiO 2 powder suspension containing monomer and polyelectrolyte (NaPSS). The composite layers were obtained on Pt and Ti substrate electrodes. The p-n junctions were char- acterized by SEM and SIMS techniques and their photoelec- trochemical activity was tested by cyclic voltammetry (cv) and chronopotentiometry (cha) registered in dark and under visible light illumination. Monomer 3,4-ethylenedioxythiophene (EDOT) (Bayer Co) was 97% grade and used as received. Poly(sodium 4-styrenesulphonate (NaPSS) (Aldrich), Na 2 SO 4 (Eurochem BGD), KCl (≥ 99.5% Fluka) were of analytical grade and used as received. Electrochemical measurements (cyclic voltammetry, chronoamperometry) in the dark and under visible light illumi- nation were performed by the potentiostat-galvanostat system AutoLab PGStat 10 in a standard three-electrode assembly with quartz window and cooling jacket (20 ◦ C). The cell 199