Solar energy is typically referred to a source of "renewable" energy. In the past few decades, inorganic solar cells have attracted a large number of academic and industrial research groups to investigate because of the high conversion efficiency and good sustainability. But semiconductor-grade silicon wafers are still relatively expensive, so great efforts have been put into the development of potentially cheaper organic solar cells. Organic materials are diverse, versatile and compatible with plastic and other flexible substrates; and devices can therefore be fabricated with low-cost, high throughput printing techniques that consume less energy and require less capital investment than silicon-based devices and other thin-film technologies. Here we review recent developments of inorganic and organic solar cells, and expect this article is helpful for understanding the field of organic solar cells.