At a silicon factory in China’s northwestern desert, Uyghur workers man electric furnaces that reach more than 2,000 degrees. Those with college degrees can earn about $600 a month running the power supply; others inspect and load products onto trucks or crush silicon for $6.50 a ton at a sister plant farther west. All must be able to speak Mandarin and have a clean “political record,” according to job ads for the company, Hoshine Silicon, the top producer of metallurgical-grade silicon (MGS) — the key raw material of polysilicon used in solar panels. The workers should be able to “bear hardship,” the ads say.

According to company reports, local propaganda and other public documents, Hoshine Silicon, also known as Hesheng, recruits and employs Uyghurs and other minorities via state labor programs that aim to place them in factories. Researchers say these programs are a form of forced labor for residents who, faced with the threat of detention or other punishment, cannot refuse.

Chinese companies in the Xinjiang region, where officials stand accused of a campaign of repression against Muslims, produce almost half the world’s solar-grade polysilicon that goes into panels sold in the United States and elsewhere. From its three factories in Xinjiang, Hoshine has produced MGS for at least eight of the world’s largest polysilicon makers, according to the company’s public statements and annual reports. Together, analysts say, these firms account for nearly all the supply of solar-grade polysilicon.

“Because they are all customers of Hoshine, the solar value chain is almost completely contaminated by forced labor,” said Johannes Bernreuter, a market research analyst who studies the polysilicon industry.

The availability of cheap coal-fired energy and labor in Xinjiang has enabled Hoshine and Chinese polysilicon makers to dominate the solar industry, making it difficult for manufacturers to replace them. Hoshine — which has previously described its hiring of minorities in Xinjiang as responding to government calls to develop the region — did not respond to requests for comment for this report.