Study and comparison of conducting polymer hole injection layers in light emitting devices C. Tengstedt a, * , A. Crispin b , C.-H. Hsu c , C. Zhang d , I.D. Parker d , W.R. Salaneck b , M. Fahlman a a Department of Science and Technology, Linko ¨ping University, SE-601 74 Norrko ¨ping, Sweden b Department of Physics, Linko ¨ping University, SE-581 83 Linko ¨ping, Sweden c Dupont Displays, The Experimental Station, Wilmington, DE 19880, USA d Dupont Displays, Santa Barbara, CA 93117, USA Received 3 August 2004; received in revised form 18 November 2004; accepted 5 February 2005 Available online 17 March 2005 Abstract A set of polyaniline- and poly(3,4-ethylene dioxythiophene)-based materials were studied as hole injection layers in polymer light emitting devices. The choice of polymeric counterion/dopant poly(styrenesulfonic acid), and poly(acry- lamido-2-methyl-1-propanesulfonic acid), and poly(acrylamide) blended with polyaniline/poly(acrylamido-2-methyl- 1-propanesulfonic acid) was found to influence both work function and film morphology, which in turn affects device performance. The work functions of the polymer films spanned the range of over 1 eV and the surface region of the films were found to be low in conducting polymer content compared to the bulk. This was particularly the case of the polyaniline/poly(acrylamido-2-methyl-1-propanesulfonic acid) blended with poly(acrylamide) which showed device efficiency equal to that of the poly(3,4-ethylene dioxythiophene)–poly(styrenesulfonic acid) reference. The turn on volt- age, however, was significantly larger, likely due to the insulating poly(acrylamide)-rich surface region of the polyan- iline/poly(acrylamido-2-methyl-1-propanesulfonic acid)/poly(acrylamide) film. The polymer blend of polyaniline/ poly(styrenesulfonic acid) yielded the highest work function (5.5 ± 0.1 eV). Ó 2005 Elsevier B.V. All rights reserved. PACS: 71.20.Rv; 68.47.Mn Keywords: Polyaniline; PEDOT; Poly(acrylamido-2-methyl-1-propanesulfonic acid); Poly(styrenesulfonic acid); Poly(acrylamide); Photoelectron spectroscopy 1566-1199/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.orgel.2005.02.001 * Corresponding author. Tel.: +46 13 282471; fax: +46 13 288969. E-mail address: carte@ifm.liu.se (C. Tengstedt). Organic Electronics 6 (2005) 21–33 www.elsevier.com/locate/orgel