Journal of Photochemistry and Photobiology A: Chemistry 247 (2012) 52–62 Contents lists available at SciVerse ScienceDirect Journal of Photochemistry and Photobiology A: Chemistry journa l h o me pag e: www.elsevier.com/locate/jphotochem Synthesis of conjugated perylene diimide-based copolymer with 5,5 ′ -bis(4-aminophenyl)-2-2 ′ -bifuryl moiety as an active material for organic photovoltaics Michael Ruby Raj a , Sambandam Anandan a,∗ , Rajadurai Vijay Solomon b , Ponnambalam Venuvanalingam b,∗ , S. Sundar Kumar Iyer c,∗ , Muthupandian Ashokkumar d,∗∗ a Nanomaterials & Solar Energy Conversion Lab, Department of Chemistry, National Institute of Technology, Tiruchirappalli 620 015, India b School of Chemistry, Bharathidasan University, Tiruchirappalli 620 024, India c Department of Electrical Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, India d School of Chemistry, University of Melbourne, Vic 3010, Australia a r t i c l e i n f o Article history: Received 26 December 2011 Received in revised form 6 July 2012 Accepted 17 July 2012 Available online 30 August 2012 Keywords: Conjugated copolymer Bulk heterojunction Solar cell DFT calculations a b s t r a c t In this study, we have synthesized conjugated n-type perylene tetracarboxylic diimide-based copolymer with 5,5 ′ -bis(4-aminophenyl)-2-2 ′ -bifuryl segment (PTCDI-PFDA) as an active material for the fabrication of bulk heterojunction photovoltaic device of type ITO/PEDOT:PSS/rr-P3HT:PTCDI-PFDA/Al. The synthe- sized n-type copolymer (an oligomer with a relatively low molecular weight) was characterized by 1 H NMR, gel permeation chromatography and thermo gravimetric analysis. The electronic and structural properties of the copolymer were investigated by UV–vis and fluorescence spectroscopy. The copoly- mer exhibited an optical band gap of about 1.59 eV. The HOMO and LUMO energy levels were calculated using cyclic voltammetry and density functional theory (DFT). The resulting copolymer was experimen- tally found to possess low-lying HOMO (ca. -5.24 eV) and high-lying LUMO (ca. -3.9 eV) energy levels. The fabricated device (D1) delivered an efficiency () of about 0.34% with a high open circuit voltage (V oc = 0.92 V), current density (J sc = 2.83 mA/cm 2 ), and fill factor (FF = 13%) under 100 mW/cm 2 white light. © 2012 Elsevier B.V. All rights reserved. 1. Introduction As an alternative to the mainstream silicon solar cells, a world- wide search is on for new types of solar cells that can be produced at low cost [1–4]. Organic photovoltaics (PVs) based on conjugated polymers have the potential to harness solar energy in a cost- effective way because of their virtue of lightweight, flexibility and easy fabrication [1,5]. Consequently, the efficiencies of conjugated polymer-based PV cells received a major boost with implementa- tion of the bulk heterojunction (BHJ) concept consisting of electron donor and acceptor molecules in a disordered bicontinuous inter- penetrating network [4,6]. The distributed donor/acceptor BHJ on a nanoscale facilitates effective dissociation of photoinduced strongly-bound excitons (electron–hole pairs) into free charges across the active layer while maintaining exciton diffusion length of ∗ Corresponding authors. ∗∗ Corresponding author. Tel.: +61 3 83447090. E-mail addresses: sanand@nitt.edu (S. Anandan), venuvanalingam@yahoo.com (P. Venuvanalingam), sskiyer@iitk.ac.in (S.S.K. Iyer), masho@unimelb.edu.au (M. Ashokkumar). conjugated polymer ∼10 nm at the donor/acceptor interface [7,8]. Simultaneously, the sufficient percolation pathways of donors and acceptors allow the charge carriers to migrate towards the elec- trodes via different phases. Thus, a successful BHJ polymer solar device fabricated to date consists of blended regioregular 2,5-diyl- poly(3-hexylthiophene) (rr-P3HT) as a donor and a derivative of fullerene ([6,6]-phenyl-C16-butyric acid methyl ester; PCBM) as an acceptor and delivers a bottle-neck in achieving high power conver- sion efficiency values (4–5%) [9,10]. The reason is rr-P3HT polymer absorbs up to 22% of the influx photons of solar spectrum fol- lowed by fullerene-based materials (PCBM). However, BHJ devices made from PCBM are generally less efficient with some excep- tions [11]. This is because, there are some drawbacks of PCBM in electronic and optoelectronic device applications, which are prob- ably due to their weak molar absorption coefficient at the visible region and the possibility of phase separation from the polymer donors. In addition, fullerene (PCBM) derivatives may lead to (i) unmatched energy levels yielding a low open circuit voltage (V oc ) and (ii) the formation of micrometer-sized PCBM phase-segregated domains resulting in low charge carrier mobility which leads to a low short circuit current (J sc ) and a fill factor (FF). Consequently, it is important to pursuit for an alternative approach by replacing 1010-6030/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jphotochem.2012.07.019