In contrast to inorganic solar cells,organic solar cells (OSCs) show advantages such as low cost,light weight,and flexibility.In fact,the most attractive feature of OSCs is that they could be produced in large scale and at low cost by roll-to-roll printing,just like printing newspapers,which does not involve complicated and high-cost procedures that are required in the production of inorganic solar cells.It is this fascinating feature that has drawn great attention on the OSC study during the past two decades.