Thin Solid Films 415 (2002) 206–210 0040-6090/02/$ - see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0040-6090 Ž 02 . 00553-9 Influence of film thickness on charge transport of electrodeposited polypyrrole thin films R. Valaski , S. Ayoub , L. Micaroni , I.A. Hummelgen * a b b a, ¨ Departamento de Fısica, Universidade Federal do Parana, Caixa Postal 19044, 81531-990 Curitiba PR, Brazil a ´ ´ Departamento de Quımica, Universidade Federal do Parana, Caixa Postal 19081, 81531-990 Curitiba PR, Brazil b ´ ´ Received 4 March 2002; received in revised form 29 May 2002; accepted 18 June 2002 Abstract We report the investigation of charge transport properties of thin electrodeposited polypyrrole (PPy) films. The charge transport in these films is limited by thermionic injection and an expression for thermionic injection into low mobility materials is used to evaluate the energy barrier between electrodes (tin-oxide, Al and Ni) and PPy. Using the same expression, we estimate the positive charge carrier mobility, demonstrating that its value is higher for thinner films.  2002 Elsevier Science B.V. All rights reserved. Keywords: Electrical properties and measurements; Organic semiconductors; Polymers; Tin oxide 1. Introduction The association of interesting properties, like mechan- ical flexibility, with semiconducting behavior makes conjugated polymers attractive for electronic and optoe- lectronic device applications. Additionally, organic sem- iconductors processing technology is simpler and consequently, less expensive than the inorganic counter- part, so that the possibility of construction of cheap flexible devices opens new potential market niches. Due to this application potentiality, some of these polymers, e.g. polyaniline, polypyrrole, polythiophene, poly-p- phenylene, polyfluorene, poly(p-phenylenevinylene) and their derivatives, are subject of intense research activity in recent years. Polypyrrole (PPy), for example, found application as transparent electrode in organic light-emitting diodes substituting traditionally used oxides w1x, in photoelec- trochemical cells w2x, in intrinsically conducting shield- ing adhesives w3x, in sensors of nitrogen oxides w4x and in rectifying double layer devices w5x,w6x. *Corresponding author. Tel.: q55-41-361-3278; fax: q55-41-267- 4236. E-mail address: iah@fisica.ufpr.br (I.A. Hummelgen). ¨ An important characteristic that differentiates PPy from other conjugated polymers widely used in organic optoelectronics, like polythiophene and poly(p-pheny- lenevinylene), is its small electroaffinity and ionization potential. So, a potential barrier for charge carriers is expected at the interface formed with PPy and these materials, implying in a rectifying character of the junction w7x. We have recently investigated electrodeposited poly- pyrrole (PPy) thin films using Au and tin-oxide (TO) as deposition substrates w8x. We found that film mor- phology and roughness are strongly influenced by sub- strate choice. We determined the electrical conductivity of PPy films and estimated the positive charge carrier mobility and charge carrier concentration in PPy. Com- paring the onset potentials for oxidation in the cyclic voltammograms of PPy and poly(3-methylthiophene) we constructed the energy level diagram of PPy. In the previous contribution w8x, however, we where not able to describe the current–voltage I(V) characteristics of TOyPPy yNi and Au yPPyyAl devices, in case of thinner samples (thickness lower than 300 nm). In this contri- bution, we present results with those devices and present an explanation of the curves based on published charge injection and transport models.