ABSTRACT

Organic solar cells (OSCs) have attracted considerable attention as clean-energy technology. With the growth in world population and economic development, more and more energy is needed. While the current energy supply relies heavily on fossil fuel sources, such as oil, coal, and natural gas, there are associated problems. First, these energy resources are finite, which cannot be recovered; second, combusting fossil fuels releases carbon dioxide, which leads to greenhouse effect and global warming; third, the combustion of fossil fuels also leads to air pollution, which is a severe problem in developing countries now. To solve these problems and meet the world’s future energy demand, renewable and clean energy is needed. Currently, solar, wind, biomass, and hydropower are the main renewable energy resources. Among them, solar energy is 34the most abundant renewable energy that could solve the energy demands in the future. The solar energy that strikes the earth in 1 h can provide enough energy to power the entire world for a whole year [1]. Among the solar cell technologies, OSCs have emerged as a promising candidate that can greatly improve the economic and environmental performance ofthe solar industry. OSCs are made from abundant, nontoxic organic materials in a layered structure, which can be processed onto plastic rolls through solution-phase large-scale printing techniques such as roll-to-roll printing, ink injecting, and spray coating, etc. [2–4]. The cost of OSCs is, hence, much lower than that of the inorganic solar cells [5]. Organic materials are light weight and color-tunable, allowing their application in wearable electronics. OSC technologies have also shown the potential for lowering the environmental impact compared to conventional silicon-based solar cell technologies [5]. These unique features make them a major player in the energy marketplace [4, 6–8]. Up to date, the world record of OSC efficiency is reported to be 14.2% in literature [9], and 13.2% in commercialized industry by Heliatek [10].