ABSTRACT
Sunlight is an abundant and renewable energy resource, and converting sunlight into electricity has been regarded as one of the most promising approaches to provide clean alternative energy compared to traditional fossil fuels. Conventional silicon solar cells generally require high purity materials and sophisticated vacuum-based processing making them expensive to fabricate, and hence, the cost per watt is much higher than fossil fuels. On the other hand, organic solar cells have attracted considerable attention in the last decade due to their low-cost fabrication, easy processing and compatibility with flexible substrates. Since most of these cells can be processed and fabricated from solutions, they can be easily manufactured by a variety of low-cost techniques including roll-to-roll printing (Krebs et al. 2009a; Søndergaard et al. 2012), inkjet printing (Schilinsky et al. 2006; Hoth et al. 2007; Aernouts et al. 2008), spray coating (Vak et al. 2007; Green et al. 2008; Kang et al. 2012), dip coating (Li et al. 2011) and screen printing (Krebs et al. 2009b). Polymer–fullerene solar cells have recently achieved 24efficiency exceeding 10% (Chemicals 2012). In spite of such potential advantages, they still lack commercial realization due to their lower efficiency and operation lifetime compared to single-crystalline silicon solar cells (Manceau et al. 2011; Jørgensen et al. 2012). To solve these issues, researchers are working vigorously to understand photo-physics of semiconducting polymers and formulating new designs and improvements to overcome such shortcomings encountered currently by organic solar cells.
