Organic solar cells based on conjugated polymers : History and recent advances

Organic solar cells have attracted huge attention because of their potential in the low-cost manufacturing of plastic solar modules featuring flexible, lightweight, ultrathin, rollable and bendable shapes. The power conversion efficiency of organic solar cells is now passing ~10%, which is a critical sign toward commercialization because organic solar cells surpass any other types of solar cells in terms of development speed. The encouraging efficiency enhancement could be realized by introducing a ‘bulk heterojunction’ concept that overcomes the weakness of organic semiconductors by minimizing their charge transport paths through making effective p-n junctions inside bulk organic films. However, there are several hurdles for commercialization, including stability and lifetime issues, owing to the bulk heterojunction concept. This review summarizes the important aspects of organic solar cells, particularly focusing on conjugated polymers as an active layer component.