Researchers estimate that global PV module waste, 90% of which are made from crystalline silicon, will reach 1.7-1.8 million tonnes by 2030 and 60-78 million tonnes by 2050, which will likely reach the same order of magnitude as global electronic waste. A novel upcycling strategy adds value to this otherwise economically low-value waste silicon. With proper chemical doping, it allows silicon waste to be turned into high-performance thermoelectrics for heat energy harvesting.