The invention describes a novel thermoelectric composite material containing electrically conductive polymeric fibrils in a polymer matrix with a high thermoelectric coefficient. The invention also includes a thermoelectric device using the composite. The invention also includes a thermoelectric device containing a thermoelectric layers and a thermoelectric device in which a thermal barrier isolates a thermoelectric layer from a structurally supporting substrate. The thermoelectric devices can be used to generate electricity or to control temperature.