journal homepage: www.elsevier.com/locate/nanoenergy Available online at www.sciencedirect.com FULL PAPER In-depth considerations for better polyelectrolytes as interfacial materials in polymer solar cells Jun-Seok Yeo a , Minji Kang a , Yen-Sook Jung a , Rira Kang a , Seung-Hoon Lee a , Youn-Jung Heo a , Sung-Ho Jin b , Dong-Yu Kim a,n , Seok-In Na c,nn a Heeger Center for Advanced Materials (HCAM), School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712, Republic of Korea b Department of Chemistry Education, Pusan National University, Busan 609-735, Republic of Korea c Professional Graduate School of Flexible and Printable Electronics and Polymer Materials Fusion Research Center, Chonbuk National University, Jeonju-si, Jeollabuk-do 561-756, Republic of Korea Received 12 August 2015; received in revised form 29 December 2015; accepted 8 January 2016 Available online 14 January 2016 KEYWORDS Polymer solar cells; Polyelectrolytes; Interlayers; Interfacial dipoles; Doping Abstract We perform a comprehensive study to achieve better polyelectrolytes (PEs) as electron- transport layers (ETLs) in polymer solar cells (PSCs). Three well-known PEs – PFN, PEIE, and WPF – are chosen as model systems and investigated with variations in their backbone structures and the state of the amine functionalities on their side chains. Respectively optimized PSCs using the three PEs exhibit different cell-performances, mainly owing to the diode characteristics of built-in potential and recombination strength. To identify how such deviated device- performances correlate with the structural features of PEs, the modulated interfaces of ITO/ PEs and PEs/active layer are studied in detail. It is found that conjugated backbones and larger counter-anions on side chains can promote the modulation of ITO work functions (WFs) and that a large amount of protonated amines on PEs is beneficial for junction properties with a subsequent active layer. Additionally, our results indicate that interfacial dipole and electrical doping between the PE and active layer, in addition to WF modulation of the ITO cathode, are http://dx.doi.org/10.1016/j.nanoen.2016.01.003 2211-2855/& 2016 Elsevier Ltd. All rights reserved. n Corresponding author. Tel.: + 82 62 715 2319; fax: + 82 62 715 2304. nn Corresponding author. Tel.: + 82 63 270 4465; fax: + 82 63 270 2341. E-mail addresses: kimdy@gist.ac.kr (D.-Y. Kim), nsi12@jbnu.ac.kr (S.-I. Na). Nano Energy (2016) 21, 26–38