**6. Outlook**

In the past four decades, the CIGS thin film solar cells have developed steadily. The lab efficiency of the CIGS solar cells has reached to as high as 22.6% [2]. However, the journey to successful large-scale commercialization is going through fire and water. Nowadays the silicon photovoltaic industry has entered its maturity stage from the industry life cycle point of view. It is ambiguous to estimate that whether the CIGS thin film solar cell is in its introduction stage or in a growth stage. Since very few CIGS companies survive in such an intensively competitive photovoltaic market, it is difficult to conclude that the CIGS is in a growth stage. It is worth noting that new concept solar cells such as the perovskite solar cells are in an astonishing development in recent years, which might make the club of the thin film solar cells more uncertain. The prospect for the CIGS thin film solar cells is facing challenges coming from both the technology and market. For achieving the great expectation of the CIGS photovoltaics, there is still a long way to go.
