Comparative study of spectral and morphological properties of blends of P3HT with PCBM and ICBA You-Heng Lin a , Yu-Tang Tsai a , Chung-Chih Wu a,⇑ , Chih-Hung Tsai b , Chien-Hung Chiang c , Hsiu-Fu Hsu c , Jey-Jau Lee d , Ching-Yuan Cheng d a Graduate Institute of Photonic and Optoelectronics, Department of Electrical Engineering, Graduate Institute of Electronics Engineering, and Innovative Photonics Advanced Research Center (i-PARC), National Taiwan University, Taipei 10617, Taiwan, ROC b Department of Opto-Electronic Engineering, National Dong Hwa University, Hualien 97401, Taiwan, ROC c Department of Chemistry, Tamkang University, Taipei 25137, Taiwan, ROC d National Synchrotron Radiation Research Center (NSRRC), Hsin-Chu 30076, Taiwan, ROC article info Article history: Received 21 June 2012 Received in revised form 13 July 2012 Accepted 15 July 2012 Available online 1 August 2012 Keywords: GIXS Polymer solar cells Fullerene Poly(3-hexylthiophene) Morphology abstract We report a comparative study on spectral and morphological properties of two blend systems for polymer solar cells: the donor material poly(3-hexylthiophene) (P3HT) in combination with the acceptor material of either [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM) or indene-C 60 bisadduct (ICBA) that was reported to enhance efficiencies of polymer solar cells. Optical microscopy and grazing incidence X-ray scattering reveal the stronger tendency of PCBM to from larger and more ordered domains/grains than ICBA either in pure or blend films. Compared to PCBM, the presence of ICBA also substantially perturbs the organization and longer-range ordering of P3HT in increasing the ICBA ratio in blends. With larger and more ordered phase-separated domains, the P3HT/PCBM blend films exhibit significant optical scattering at higher PCBM ratios. Yet, such optical scatter- ing is not significant for P3HT/ICBA blends (even with high ICBA ratios). Overall, results here suggest the reported higher efficiencies of P3HT/ICBA solar cells (vs. P3HT/PCBM cells) cannot be attributed to larger and/or more ordered phase-separated donor–acceptor domains and other characteristics play more important roles in this case. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Organic photovoltaics (OPVs) have attracted wide attention in recent years due to their potential advantages in fabrication, cost, and mechanical flexibility [1–3]. The energy conversion process in OPVs typically involves exci- ton generation upon light absorption, exciton diffusion and then dissociation of excitons into free carriers at the donor–acceptor (D–A) interface, and finally transport of carriers to their respective electrodes [1–3]. To achieve high conversion efficiencies, polymer bulk-heterojunctions (BHJ) composed of nanoscale interpenetrated (phase- separated) domains of donor and acceptor materials are introduced to increase areas of D–A interfaces for ensur- ing effective exciton diffusion to such interfaces, mean- while providing transport paths for carrier transport/ extraction to electrodes [4]. Among various D–A materi- als, poly(3-hexylthiophene) (P3HT) as a donor and [6,6]- phenyl-C 61 butyric acid methyl ester (PCBM) as an accep- tor are the most widely studied D–A combination [5–14], in considering light harvesting, carrier generation and carrier transport. Regioregular P3HT are known to have strong tendency of forming self-organized structure in thin films, which could be further enhanced upon appro- priate treatments (e.g. thermal annealing, solvent anneal- ing, etc.) [6–12]. More ordered molecular packing benefits charge transport (i.e., higher mobility) and absorption at longer wavelengths due to enhanced inter- chain interactions [6]. In BHJs, such treatments induce not only re-crystallization but also inter-diffusion of D/A 1566-1199/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.orgel.2012.07.023 ⇑ Corresponding author. Tel.: +886 2 33663636; fax: +886 2 33669404. E-mail address: chungwu@cc.ee.ntu.edu.tw (C.-C. Wu). Organic Electronics 13 (2012) 2333–2341 Contents lists available at SciVerse ScienceDirect Organic Electronics journal homepage: www.elsevier.com/locate/orgel