Abstract: One of the key factors in the fabrication of high performance solar cells is improving the energy conversion efficiency. Lower conversion efficiency is a bottle-neck for the commercial production of organic solar cells. We present the basic principles of organic photovoltaic devices and current research progress. In particular, several effective ways for enhancing the efficiency of organic solar cells, such as improving the open circuit voltage, short circuit current, photoelectric conversion efficiency, and fill factor, are analyzed and summarized.The stability of organic solar cells is also discussed.