There seems to be a pretty good chance the answer is, "Yes." Chinese Solar Companies Tied to Use of Forced Labor - The New York Times
The propaganda says that the Uighur minority Muslims from Xinjiang were happy to go to work for the world’s second-largest manufacturer of polysilicon, a key component of solar panels.
But researchers and human rights experts say those positive images may conceal a more troubling reality — the persecution of one of China’s most vulnerable ethnic groups. According to a report by the consultancy Horizon Advisory, Xinjiang’s rising solar energy technology sector is connected to a broad program of assigned labor in China, including methods that fit well-documented patterns of forced labor.
Forced Labor is New York Times speak for, "It's really slavery, but we don't want to insult our Chinese masters." Or something. (Hat tip.)