Using silicon as a 'thermoelectric' material to convert heat into electricity would be a technological leap forward. But silicon conducts heat so well that nobody thought that could work — until now.Thermoelectric materials convert heat into electric current, and vice versa. If they could be made more efficient at that conversion, they might be used to suck up waste heat from fossil-fuel combustion processes to make electric current, or as an alternative to photovoltaic cells for converting solar warmth into elec-tricity1.